[ceph.git] / ceph / doc / dev / index.rst

============================================
Contributing to Ceph: A Guide for Developers
============================================

:Author: Loic Dachary
:Author: Nathan Cutler
:License: Creative Commons Attribution-ShareAlike (CC BY-SA)

.. note:: The old (pre-2016) developer documentation has been moved to :doc:`/dev/index-old`.

.. contents::
   :depth: 3

Introduction
============

This guide has two aims. First, it should lower the barrier to entry for
software developers who wish to get involved in the Ceph project. Second,
it should serve as a reference for Ceph developers.

We assume that readers are already familiar with Ceph (the distributed
object store and file system designed to provide excellent performance,
reliability and scalability). If not, please refer to the `project website`_
and especially the `publications list`_.

.. _`project website`: http://ceph.com
.. _`publications list`: https://ceph.com/resources/publications/

Since this document is to be consumed by developers, who are assumed to
have Internet access, topics covered elsewhere, either within the Ceph
documentation or elsewhere on the web, are treated by linking. If you
notice that a link is broken or if you know of a better link, please
`report it as a bug`_.

.. _`report it as a bug`: http://tracker.ceph.com/projects/ceph/issues/new

Essentials (tl;dr)
==================

This chapter presents essential information that every Ceph developer needs
to know.

Leads
-----

The Ceph project is led by Sage Weil. In addition, each major project
component has its own lead. The following table shows all the leads and
their nicks on `GitHub`_:

.. _github: https://github.com/

========= =============== =============
Scope     Lead            GitHub nick
========= =============== =============
Ceph      Sage Weil       liewegas
RADOS     Samuel Just     athanatos
RGW       Yehuda Sadeh    yehudasa
RBD       Jason Dillaman  dillaman
CephFS    John Spray      jcsp
Build/Ops Ken Dreyer      ktdreyer
========= =============== =============

The Ceph-specific acronyms in the table are explained in
:doc:`/architecture`.

History
-------

See the `History chapter of the Wikipedia article`_.

.. _`History chapter of the Wikipedia article`: https://en.wikipedia.org/wiki/Ceph_%28software%29#History

Licensing
---------

Ceph is free software.

Unless stated otherwise, the Ceph source code is distributed under the terms of
the LGPL2.1. For full details, see `the file COPYING in the top-level
directory of the source-code tree`_.

.. _`the file COPYING in the top-level directory of the source-code tree`:
  https://github.com/ceph/ceph/blob/master/COPYING

Source code repositories
------------------------

The source code of Ceph lives on `GitHub`_ in a number of repositories below
the `Ceph "organization"`_.

.. _`Ceph "organization"`: https://github.com/ceph

To make a meaningful contribution to the project as a developer, a working
knowledge of git_ is essential.

.. _git: https://git-scm.com/documentation

Although the `Ceph "organization"`_ includes several software repositories,
this document covers only one: https://github.com/ceph/ceph.

Redmine issue tracker
---------------------

Although `GitHub`_ is used for code, Ceph-related issues (Bugs, Features,
Backports, Documentation, etc.) are tracked at http://tracker.ceph.com,
which is powered by `Redmine`_.

.. _Redmine: http://www.redmine.org

The tracker has a Ceph project with a number of subprojects loosely
corresponding to the various architectural components (see
:doc:`/architecture`).

Mere `registration`_ in the tracker automatically grants permissions
sufficient to open new issues and comment on existing ones.

.. _registration: http://tracker.ceph.com/account/register

To report a bug or propose a new feature, `jump to the Ceph project`_ and
click on `New issue`_.

.. _`jump to the Ceph project`: http://tracker.ceph.com/projects/ceph
.. _`New issue`: http://tracker.ceph.com/projects/ceph/issues/new

Mailing list
------------

Ceph development email discussions take place on the mailing list
``ceph-devel@vger.kernel.org``. The list is open to all. Subscribe by
sending a message to ``majordomo@vger.kernel.org`` with the line: ::

    subscribe ceph-devel

in the body of the message.

There are also `other Ceph-related mailing lists`_.

.. _`other Ceph-related mailing lists`: https://ceph.com/irc/

IRC
---

In addition to mailing lists, the Ceph community also communicates in real
time using `Internet Relay Chat`_.

.. _`Internet Relay Chat`: http://www.irchelp.org/

See https://ceph.com/irc/ for how to set up your IRC
client and a list of channels.

Submitting patches
------------------

The canonical instructions for submitting patches are contained in the
`the file CONTRIBUTING.rst in the top-level directory of the source-code
tree`_. There may be some overlap between this guide and that file.

.. _`the file CONTRIBUTING.rst in the top-level directory of the source-code tree`:
  https://github.com/ceph/ceph/blob/master/CONTRIBUTING.rst

All newcomers are encouraged to read that file carefully.

Building from source
--------------------

See instructions at :doc:`/install/build-ceph`.

Using ccache to speed up local builds
-------------------------------------

Rebuilds of the ceph source tree can benefit significantly from use of `ccache`_.
Many a times while switching branches and such, one might see build failures for
certain older branches mostly due to older build artifacts. These rebuilds can
significantly benefit the use of ccache. For a full clean source tree, one could
do ::

  $ make clean

  # note the following will nuke everything in the source tree that
  # isn't tracked by git, so make sure to backup any log files /conf options

  $ git clean -fdx; git submodule foreach git clean -fdx

ccache is available as a package in most distros. To build ceph with ccache one
can::

  $ cmake -DWITH_CCACHE=ON ..

ccache can also be used for speeding up all builds in the system. for more
details refer to the `run modes`_ of the ccache manual. The default settings of
``ccache`` can be displayed with ``ccache -s``.

.. note: It is recommended to override the ``max_size``, which is the size of
   cache, defaulting to 10G, to a larger size like 25G or so. Refer to the
   `configuration`_ section of ccache manual.

.. _`ccache`: https://ccache.samba.org/
.. _`run modes`: https://ccache.samba.org/manual.html#_run_modes
.. _`configuration`: https://ccache.samba.org/manual.html#_configuration

Development-mode cluster
------------------------

See :doc:`/dev/quick_guide`.

Backporting
-----------

All bugfixes should be merged to the ``master`` branch before being backported.
To flag a bugfix for backporting, make sure it has a `tracker issue`_
associated with it and set the ``Backport`` field to a comma-separated list of
previous releases (e.g. "hammer,jewel") that you think need the backport.
The rest (including the actual backporting) will be taken care of by the
`Stable Releases and Backports`_ team.

.. _`tracker issue`: http://tracker.ceph.com/
.. _`Stable Releases and Backports`: http://tracker.ceph.com/projects/ceph-releases/wiki


What is merged where and when ?
===============================

Commits are merged into branches according to criteria that change
during the lifecycle of a Ceph release. This chapter is the inventory
of what can be merged in which branch at a given point in time.

Development releases (i.e. x.0.z)
---------------------------------

What ?
^^^^^^

* features
* bug fixes

Where ?
^^^^^^^

Features are merged to the master branch. Bug fixes should be merged
to the corresponding named branch (e.g. "jewel" for 10.0.z, "kraken"
for 11.0.z, etc.). However, this is not mandatory - bug fixes can be
merged to the master branch as well, since the master branch is
periodically merged to the named branch during the development
releases phase. In either case, if the bugfix is important it can also
be flagged for backport to one or more previous stable releases.

When ?
^^^^^^

After the stable release candidates of the previous release enters
phase 2 (see below).  For example: the "jewel" named branch was
created when the infernalis release candidates entered phase 2. From
this point on, master was no longer associated with infernalis. As
soon as the named branch of the next stable release is created, master
starts getting periodically merged into it.

Branch merges
^^^^^^^^^^^^^

* The branch of the stable release is merged periodically into master.
* The master branch is merged periodically into the branch of the
  stable release.
* The master is merged into the branch of the stable release
  immediately after each development x.0.z release.
  
Stable release candidates (i.e. x.1.z) phase 1
----------------------------------------------

What ?
^^^^^^

* bug fixes only

Where ?
^^^^^^^

The branch of the stable release (e.g. "jewel" for 10.0.z, "kraken"
for 11.0.z, etc.) or master.  Bug fixes should be merged to the named
branch corresponding to the stable release candidate (e.g. "jewel" for
10.1.z) or to master. During this phase, all commits to master will be
merged to the named branch, and vice versa. In other words, it makes
no difference whether a commit is merged to the named branch or to
master - it will make it into the next release candidate either way.

When ?
^^^^^^

After the first stable release candidate is published, i.e. after the
x.1.0 tag is set in the release branch.

Branch merges
^^^^^^^^^^^^^

* The branch of the stable release is merged periodically into master.
* The master branch is merged periodically into the branch of the
  stable release.
* The master is merged into the branch of the stable release
  immediately after each x.1.z release candidate.

Stable release candidates (i.e. x.1.z) phase 2
----------------------------------------------

What ?
^^^^^^

* bug fixes only

Where ?
^^^^^^^

The branch of the stable release (e.g. "jewel" for 10.0.z, "kraken"
for 11.0.z, etc.). During this phase, all commits to the named branch
will be merged into master. Cherry-picking to the named branch during
release candidate phase 2 is done manually since the official
backporting process only begins when the release is pronounced
"stable".

When ?
^^^^^^

After Sage Weil decides it is time for phase 2 to happen.

Branch merges
^^^^^^^^^^^^^

* The branch of the stable release is merged periodically into master.

Stable releases (i.e. x.2.z)
----------------------------

What ?
^^^^^^

* bug fixes
* features are sometime accepted
* commits should be cherry-picked from master when possible
* commits that are not cherry-picked from master must be about a bug unique to the stable release
* see also `the backport HOWTO`_

.. _`the backport HOWTO`:
  http://tracker.ceph.com/projects/ceph-releases/wiki/HOWTO#HOWTO

Where ?
^^^^^^^

The branch of the stable release (hammer for 0.94.x, infernalis for 9.2.x, etc.)

When ?
^^^^^^

After the stable release is published, i.e. after the "vx.2.0" tag is
set in the release branch.

Branch merges
^^^^^^^^^^^^^

Never

Issue tracker
=============

See `Redmine issue tracker`_ for a brief introduction to the Ceph Issue Tracker.

Ceph developers use the issue tracker to 

1. keep track of issues - bugs, fix requests, feature requests, backport
requests, etc. 

2. communicate with other developers and keep them informed as work
on the issues progresses.

Issue tracker conventions
-------------------------

When you start working on an existing issue, it's nice to let the other
developers know this - to avoid duplication of labor. Typically, this is
done by changing the :code:`Assignee` field (to yourself) and changing the
:code:`Status` to *In progress*. Newcomers to the Ceph community typically do not
have sufficient privileges to update these fields, however: they can
simply update the issue with a brief note.

.. table:: Meanings of some commonly used statuses

   ================ ===========================================
   Status           Meaning
   ================ ===========================================
   New              Initial status
   In Progress      Somebody is working on it
   Need Review      Pull request is open with a fix
   Pending Backport Fix has been merged, backport(s) pending
   Resolved         Fix and backports (if any) have been merged
   ================ ===========================================

Basic workflow
==============

The following chart illustrates basic development workflow:

.. ditaa::

            Upstream Code                       Your Local Environment

           /----------\        git clone           /-------------\
           |   Ceph   | -------------------------> | ceph/master |
           \----------/                            \-------------/
                ^                                    |
                |                                    | git branch fix_1
                | git merge                          |
                |                                    v
           /----------------\  git commit --amend   /-------------\
           |  make check    |---------------------> | ceph/fix_1  |
           | ceph--qa--suite|                       \-------------/
           \----------------/                        |
                ^                                    | fix changes
                |                                    | test changes
                | review                             | git commit
                |                                    | 
                |                                    v
           /--------------\                        /-------------\
           |   github     |<---------------------- | ceph/fix_1  |
           | pull request |         git push       \-------------/
           \--------------/

Below we present an explanation of this chart. The explanation is written
with the assumption that you, the reader, are a beginning developer who
has an idea for a bugfix, but do not know exactly how to proceed.

Update the tracker
------------------

Before you start, you should know the `Issue tracker`_ number of the bug
you intend to fix. If there is no tracker issue, now is the time to create
one. 

The tracker is there to explain the issue (bug) to your fellow Ceph
developers and keep them informed as you make progress toward resolution. 
To this end, then, provide a descriptive title as well as sufficient
information and details in the description.

If you have sufficient tracker permissions, assign the bug to yourself by
changing the ``Assignee`` field.  If your tracker permissions have not yet
been elevated, simply add a comment to the issue with a short message like
"I am working on this issue". 

Upstream code
-------------

This section, and the ones that follow, correspond to the nodes in the
above chart.

The upstream code lives in https://github.com/ceph/ceph.git, which is
sometimes referred to as the "upstream repo", or simply "upstream". As the
chart illustrates, we will make a local copy of this code, modify it, test
our modifications, and submit the modifications back to the upstream repo
for review.

A local copy of the upstream code is made by 

1. forking the upstream repo on GitHub, and 
2. cloning your fork to make a local working copy

See the `the GitHub documentation
<https://help.github.com/articles/fork-a-repo/#platform-linux>`_ for
detailed instructions on forking. In short, if your GitHub username is
"mygithubaccount", your fork of the upstream repo will show up at
https://github.com/mygithubaccount/ceph. Once you have created your fork,
you clone it by doing:

.. code::

    $ git clone https://github.com/mygithubaccount/ceph

While it is possible to clone the upstream repo directly, in this case you
must fork it first. Forking is what enables us to open a `GitHub pull
request`_.

For more information on using GitHub, refer to `GitHub Help
<https://help.github.com/>`_.

Local environment
-----------------

In the local environment created in the previous step, you now have a
copy of the ``master`` branch in ``remotes/origin/master``. Since the fork
(https://github.com/mygithubaccount/ceph.git) is frozen in time and the
upstream repo (https://github.com/ceph/ceph.git, typically abbreviated to
``ceph/ceph.git``) is updated frequently by other developers, you will need
to sync your fork periodically. To do this, first add the upstream repo as
a "remote" and fetch it::

    $ git remote add ceph https://github.com/ceph/ceph.git
    $ git fetch ceph

Fetching downloads all objects (commits, branches) that were added since
the last sync. After running these commands, all the branches from
``ceph/ceph.git`` are downloaded to the local git repo as
``remotes/ceph/$BRANCH_NAME`` and can be referenced as
``ceph/$BRANCH_NAME`` in certain git commands. 

For example, your local ``master`` branch can be reset to the upstream Ceph
``master`` branch by doing::

    $ git fetch ceph
    $ git checkout master
    $ git reset --hard ceph/master

Finally, the ``master`` branch of your fork can then be synced to upstream
master by::

    $ git push -u origin master

Bugfix branch
-------------

Next, create a branch for the bugfix:

.. code::

    $ git checkout master
    $ git checkout -b fix_1
    $ git push -u origin fix_1

This creates a ``fix_1`` branch locally and in our GitHub fork. At this
point, the ``fix_1`` branch is identical to the ``master`` branch, but not
for long! You are now ready to modify the code.

Fix bug locally
---------------

At this point, change the status of the tracker issue to "In progress" to
communicate to the other Ceph developers that you have begun working on a
fix. If you don't have permission to change that field, your comment that
you are working on the issue is sufficient.

Possibly, your fix is very simple and requires only minimal testing.
More likely, it will be an iterative process involving trial and error, not
to mention skill. An explanation of how to fix bugs is beyond the
scope of this document. Instead, we focus on the mechanics of the process
in the context of the Ceph project.

A detailed discussion of the tools available for validating your bugfixes,
see the `Testing`_ chapter.

For now, let us just assume that you have finished work on the bugfix and
that you have tested it and believe it works. Commit the changes to your local
branch using the ``--signoff`` option::

    $ git commit -as

and push the changes to your fork::

    $ git push origin fix_1

GitHub pull request
-------------------

The next step is to open a GitHub pull request. The purpose of this step is
to make your bugfix available to the community of Ceph developers.  They
will review it and may do additional testing on it.

In short, this is the point where you "go public" with your modifications.
Psychologically, you should be prepared to receive suggestions and
constructive criticism. Don't worry! In our experience, the Ceph project is
a friendly place!

If you are uncertain how to use pull requests, you may read
`this GitHub pull request tutorial`_.

.. _`this GitHub pull request tutorial`:
   https://help.github.com/articles/using-pull-requests/

For some ideas on what constitutes a "good" pull request, see
the `Git Commit Good Practice`_ article at the `OpenStack Project Wiki`_.

.. _`Git Commit Good Practice`: https://wiki.openstack.org/wiki/GitCommitMessages
.. _`OpenStack Project Wiki`: https://wiki.openstack.org/wiki/Main_Page

Once your pull request (PR) is opened, update the `Issue tracker`_ by
adding a comment to the bug pointing the other developers to your PR. The
update can be as simple as::

    *PR*: https://github.com/ceph/ceph/pull/$NUMBER_OF_YOUR_PULL_REQUEST

Automated PR validation
-----------------------

When your PR hits GitHub, the Ceph project's `Continuous Integration (CI)
<https://en.wikipedia.org/wiki/Continuous_integration>`_
infrastructure will test it automatically. At the time of this writing
(March 2016), the automated CI testing included a test to check that the
commits in the PR are properly signed (see `Submitting patches`_) and a
``make check`` test.

The latter, ``make check``, builds the PR and runs it through a battery of
tests. These tests run on machines operated by the Ceph Continuous
Integration (CI) team. When the tests complete, the result will be shown
on GitHub in the pull request itself.

You can (and should) also test your modifications before you open a PR. 
Refer to the `Testing`_ chapter for details.

Integration tests AKA ceph-qa-suite
-----------------------------------

Since Ceph is a complex beast, it may also be necessary to test your fix to
see how it behaves on real clusters running either on real or virtual
hardware. Tests designed for this purpose live in the `ceph/qa
sub-directory`_ and are run via the `teuthology framework`_.

.. _`ceph/qa sub-directory`: https://github.com/ceph/ceph/tree/master/qa/
.. _`teuthology repository`: https://github.com/ceph/teuthology
.. _`teuthology framework`: https://github.com/ceph/teuthology

If you have access to an OpenStack tenant, you are encouraged to run the
integration tests yourself using `ceph-workbench ceph-qa-suite`_,
and to post the test results to the PR.

.. _`ceph-workbench ceph-qa-suite`: http://ceph-workbench.readthedocs.org/

The Ceph community has access to the `Sepia lab
<http://ceph.github.io/sepia/>`_ where integration tests can be run on
real hardware. Other developers may add tags like "needs-qa" to your PR.
This allows PRs that need testing to be merged into a single branch and
tested all at the same time. Since teuthology suites can take hours
(even days in some cases) to run, this can save a lot of time.

Integration testing is discussed in more detail in the `Testing`_ chapter.

Code review
-----------

Once your bugfix has been thoroughly tested, or even during this process,
it will be subjected to code review by other developers. This typically
takes the form of correspondence in the PR itself, but can be supplemented
by discussions on `IRC`_ and the `Mailing list`_.

Amending your PR
----------------

While your PR is going through `Testing`_ and `Code review`_, you can
modify it at any time by editing files in your local branch.

After the changes are committed locally (to the ``fix_1`` branch in our
example), they need to be pushed to GitHub so they appear in the PR.

Modifying the PR is done by adding commits to the ``fix_1`` branch upon
which it is based, often followed by rebasing to modify the branch's git
history. See `this tutorial
<https://www.atlassian.com/git/tutorials/rewriting-history>`_ for a good
introduction to rebasing. When you are done with your modifications, you
will need to force push your branch with:

.. code::

    $ git push --force origin fix_1

Merge
-----

The bugfixing process culminates when one of the project leads decides to
merge your PR.

When this happens, it is a signal for you (or the lead who merged the PR)
to change the `Issue tracker`_ status to "Resolved". Some issues may be
flagged for backporting, in which case the status should be changed to
"Pending Backport" (see the `Backporting`_ chapter for details).


Testing
=======

Ceph has two types of tests: "make check" tests and integration tests.
The former are run via `GNU Make <https://www.gnu.org/software/make/>`,
and the latter are run via the `teuthology framework`_. The following two
chapters examine the "make check" and integration tests in detail.

Testing - make check
====================

After compiling Ceph, the ``make check`` command can be used to run the
code through a battery of tests covering various aspects of Ceph. For
inclusion in "make check", a test must:

* bind ports that do not conflict with other tests
* not require root access
* not require more than one machine to run
* complete within a few minutes

While it is possible to run ``make check`` directly, it can be tricky to
correctly set up your environment. Fortunately, a script is provided to
make it easier run "make check" on your code. It can be run from the
top-level directory of the Ceph source tree by doing::

    $ ./run-make-check.sh

You will need a minimum of 8GB of RAM and 32GB of free disk space for this
command to complete successfully on x86_64 (other architectures may have
different constraints). Depending on your hardware, it can take from 20
minutes to three hours to complete, but it's worth the wait.

Future sections
---------------

* Principles of make check tests
* Where to find test results
* How to interpret test results
* Find the corresponding source code
* Writing make check tests
* Make check caveats

Testing - integration tests
===========================

When a test requires multiple machines, root access or lasts for a
longer time (for example, to simulate a realistic Ceph deployment), it
is deemed to be an integration test. Integration tests are organized into
"suites", which are defined in the `ceph/qa sub-directory`_ and run with
the ``teuthology-suite`` command.

The ``teuthology-suite`` command is part of the `teuthology framework`_.
In the sections that follow we attempt to provide a detailed introduction
to that framework from the perspective of a beginning Ceph developer.

Teuthology consumes packages 
----------------------------

It may take some time to understand the significance of this fact, but it
is `very` significant. It means that automated tests can be conducted on
multiple platforms using the same packages (RPM, DEB) that can be
installed on any machine running those platforms.

Teuthology has a `list of platforms that it supports
<https://github.com/ceph/ceph/tree/master/qa/distros/supported>`_ (as
of March 2016 the list consisted of "CentOS 7.2" and "Ubuntu 14.04").  It
expects to be provided pre-built Ceph packages for these platforms.
Teuthology deploys these platforms on machines (bare-metal or
cloud-provisioned), installs the packages on them, and deploys Ceph
clusters on them - all as called for by the test.

The nightlies
-------------

A number of integration tests are run on a regular basis in the `Sepia
lab`_ against the official Ceph repositories (on the ``master`` development
branch and the stable branches). Traditionally, these tests are called "the
nightlies" because the Ceph core developers used to live and work in
the same time zone and from their perspective the tests were run overnight. 

The results of the nightlies are published at http://pulpito.ceph.com/ and
http://pulpito.ovh.sepia.ceph.com:8081/. The developer nick shows in the
test results URL and in the first column of the Pulpito dashboard.  The
results are also reported on the `ceph-qa mailing list
<https://ceph.com/irc/>`_ for analysis.

Suites inventory
----------------

The ``suites`` directory of the `ceph/qa sub-directory`_ contains
all the integration tests, for all the Ceph components.

`ceph-deploy <https://github.com/ceph/ceph/tree/master/qa/suites/ceph-deploy>`_
  install a Ceph cluster with ``ceph-deploy`` (`ceph-deploy man page`_)

`ceph-disk <https://github.com/ceph/ceph/tree/master/qa/suites/ceph-disk>`_
  verify init scripts (upstart etc.) and udev integration with
  ``ceph-disk`` (`ceph-disk man page`_), with and without `dmcrypt
  <https://gitlab.com/cryptsetup/cryptsetup/wikis/DMCrypt>`_ support.

`dummy <https://github.com/ceph/ceph/tree/master/qa/suites/dummy>`_
  get a machine, do nothing and return success (commonly used to
  verify the integration testing infrastructure works as expected)

`fs <https://github.com/ceph/ceph/tree/master/qa/suites/fs>`_
  test CephFS

`kcephfs <https://github.com/ceph/ceph/tree/master/qa/suites/kcephfs>`_
  test the CephFS kernel module

`krbd <https://github.com/ceph/ceph/tree/master/qa/suites/krbd>`_
  test the RBD kernel module

`powercycle <https://github.com/ceph/ceph/tree/master/qa/suites/powercycle>`_
  verify the Ceph cluster behaves when machines are powered off
  and on again

`rados <https://github.com/ceph/ceph/tree/master/qa/suites/rados>`_
  run Ceph clusters including OSDs and MONs, under various conditions of
  stress

`rbd <https://github.com/ceph/ceph/tree/master/qa/suites/rbd>`_
  run RBD tests using actual Ceph clusters, with and without qemu

`rgw <https://github.com/ceph/ceph/tree/master/qa/suites/rgw>`_
  run RGW tests using actual Ceph clusters

`smoke <https://github.com/ceph/ceph/tree/master/qa/suites/smoke>`_
  run tests that exercise the Ceph API with an actual Ceph cluster

`teuthology <https://github.com/ceph/ceph/tree/master/qa/suites/teuthology>`_
  verify that teuthology can run integration tests, with and without OpenStack

`upgrade <https://github.com/ceph/ceph/tree/master/qa/suites/upgrade>`_
  for various versions of Ceph, verify that upgrades can happen
  without disrupting an ongoing workload

.. _`ceph-deploy man page`: ../../man/8/ceph-deploy
.. _`ceph-disk man page`: ../../man/8/ceph-disk

teuthology-describe-tests
-------------------------

In February 2016, a new feature called ``teuthology-describe-tests`` was
added to the `teuthology framework`_ to facilitate documentation and better
understanding of integration tests (`feature announcement
<http://article.gmane.org/gmane.comp.file-systems.ceph.devel/29287>`_).

The upshot is that tests can be documented by embedding ``meta:``
annotations in the yaml files used to define the tests. The results can be
seen in the `ceph-qa-suite wiki
<http://tracker.ceph.com/projects/ceph-qa-suite/wiki/>`_.

Since this is a new feature, many yaml files have yet to be annotated.
Developers are encouraged to improve the documentation, in terms of both
coverage and quality.

How integration tests are run
-----------------------------

Given that - as a new Ceph developer - you will typically not have access
to the `Sepia lab`_, you may rightly ask how you can run the integration
tests in your own environment.

One option is to set up a teuthology cluster on bare metal. Though this is
a non-trivial task, it `is` possible. Here are `some notes
<http://docs.ceph.com/teuthology/docs/LAB_SETUP.html>`_ to get you started
if you decide to go this route.

If you have access to an OpenStack tenant, you have another option: the
`teuthology framework`_ has an OpenStack backend, which is documented `here
<https://github.com/dachary/teuthology/tree/openstack#openstack-backend>`__.
This OpenStack backend can build packages from a given git commit or
branch, provision VMs, install the packages and run integration tests
on those VMs. This process is controlled using a tool called
`ceph-workbench ceph-qa-suite`_. This tool also automates publishing of
test results at http://teuthology-logs.public.ceph.com. 

Running integration tests on your code contributions and publishing the
results allows reviewers to verify that changes to the code base do not
cause regressions, or to analyze test failures when they do occur.

Every teuthology cluster, whether bare-metal or cloud-provisioned, has a
so-called "teuthology machine" from which tests suites are triggered using the
``teuthology-suite`` command.

A detailed and up-to-date description of each `teuthology-suite`_ option is
available by running the following command on the teuthology machine::

   $ teuthology-suite --help

.. _teuthology-suite: http://docs.ceph.com/teuthology/docs/teuthology.suite.html

How integration tests are defined
---------------------------------

Integration tests are defined by yaml files found in the ``suites``
subdirectory of the `ceph/qa sub-directory`_ and implemented by python
code found in the ``tasks`` subdirectory. Some tests ("standalone tests")
are defined in a single yaml file, while other tests are defined by a
directory tree containing yaml files that are combined, at runtime, into a
larger yaml file.

Reading a standalone test
-------------------------

Let us first examine a standalone test, or "singleton". 

Here is a commented example using the integration test
`rados/singleton/all/admin-socket.yaml
<https://github.com/ceph/ceph/blob/master/qa/suites/rados/singleton/all/admin-socket.yaml>`_
::

      roles:
      - - mon.a
        - osd.0
        - osd.1
      tasks:
      - install:
      - ceph:
      - admin_socket:
          osd.0:
            version:
            git_version:
            help:
            config show:
            config set filestore_dump_file /tmp/foo:
            perf dump:
            perf schema:

The ``roles`` array determines the composition of the cluster (how
many MONs, OSDs, etc.) on which this test is designed to run, as well
as how these roles will be distributed over the machines in the
testing cluster. In this case, there is only one element in the
top-level array: therefore, only one machine is allocated to the
test. The nested array declares that this machine shall run a MON with
id ``a`` (that is the ``mon.a`` in the list of roles) and two OSDs
(``osd.0`` and ``osd.1``).

The body of the test is in the ``tasks`` array: each element is
evaluated in order, causing the corresponding python file found in the
``tasks`` subdirectory of the `teuthology repository`_ or
`ceph/qa sub-directory`_ to be run. "Running" in this case means calling
the ``task()`` function defined in that file.

In this case, the `install
<https://github.com/ceph/teuthology/blob/master/teuthology/task/install/__init__.py>`_
task comes first. It installs the Ceph packages on each machine (as
defined by the ``roles`` array). A full description of the ``install``
task is `found in the python file
<https://github.com/ceph/teuthology/blob/master/teuthology/task/install/__init__.py>`_
(search for "def task").

The ``ceph`` task, which is documented `here
<https://github.com/ceph/ceph/blob/master/qa/tasks/ceph.py>`__ (again,
search for "def task"), starts OSDs and MONs (and possibly MDSs as well)
as required by the ``roles`` array. In this example, it will start one MON
(``mon.a``) and two OSDs (``osd.0`` and ``osd.1``), all on the same
machine. Control moves to the next task when the Ceph cluster reaches
``HEALTH_OK`` state.

The next task is ``admin_socket`` (`source code
<https://github.com/ceph/ceph/blob/master/qa/tasks/admin_socket.py>`_).
The parameter of the ``admin_socket`` task (and any other task) is a
structure which is interpreted as documented in the task. In this example
the parameter is a set of commands to be sent to the admin socket of
``osd.0``. The task verifies that each of them returns on success (i.e.
exit code zero).

This test can be run with::

    $ teuthology-suite --suite rados/singleton/all/admin-socket.yaml fs/ext4.yaml

Test descriptions 
-----------------

Each test has a "test description", which is similar to a directory path,
but not the same. In the case of a standalone test, like the one in
`Reading a standalone test`_, the test description is identical to the
relative path (starting from the ``suites/`` directory of the
`ceph/qa sub-directory`_) of the yaml file defining the test.

Much more commonly, tests are defined not by a single yaml file, but by a
`directory tree of yaml files`. At runtime, the tree is walked and all yaml
files (facets) are combined into larger yaml "programs" that define the
tests. A full listing of the yaml defining the test is included at the
beginning of every test log.

In these cases, the description of each test consists of the
subdirectory under `suites/
<https://github.com/ceph/ceph/tree/master/qa/suites>`_ containing the
yaml facets, followed by an expression in curly braces (``{}``) consisting of
a list of yaml facets in order of concatenation. For instance the
test description::

  ceph-disk/basic/{distros/centos_7.0.yaml tasks/ceph-disk.yaml}

signifies the concatenation of two files:

* ceph-disk/basic/distros/centos_7.0.yaml
* ceph-disk/basic/tasks/ceph-disk.yaml

How are tests built from directories?
-------------------------------------

As noted in the previous section, most tests are not defined in a single
yaml file, but rather as a `combination` of files collected from a
directory tree within the ``suites/`` subdirectory of the `ceph/qa sub-directory`_. 

The set of all tests defined by a given subdirectory of ``suites/`` is
called an "integration test suite", or a "teuthology suite".

Combination of yaml facets is controlled by special files (``%`` and
``+``) that are placed within the directory tree and can be thought of as
operators.  The ``%`` file is the "convolution" operator and ``+``
signifies concatenation.

Convolution operator
--------------------

The convolution operator, implemented as an empty file called ``%``, tells
teuthology to construct a test matrix from yaml facets found in
subdirectories below the directory containing the operator.

For example, the `ceph-disk suite
<https://github.com/ceph/ceph/tree/jewel/qa/suites/ceph-disk/>`_ is
defined by the ``suites/ceph-disk/`` tree, which consists of the files and
subdirectories in the following structure::

  directory: ceph-disk/basic
      file: %
      directory: distros
         file: centos_7.0.yaml
         file: ubuntu_14.04.yaml
      directory: tasks
         file: ceph-disk.yaml

This is interpreted as a 2x1 matrix consisting of two tests: 

1. ceph-disk/basic/{distros/centos_7.0.yaml tasks/ceph-disk.yaml}
2. ceph-disk/basic/{distros/ubuntu_14.04.yaml tasks/ceph-disk.yaml}

i.e. the concatenation of centos_7.0.yaml and ceph-disk.yaml and
the concatenation of ubuntu_14.04.yaml and ceph-disk.yaml, respectively.
In human terms, this means that the task found in ``ceph-disk.yaml`` is
intended to run on both CentOS 7.0 and Ubuntu 14.04.

Without the file percent, the ``ceph-disk`` tree would be interpreted as
three standalone tests:

* ceph-disk/basic/distros/centos_7.0.yaml
* ceph-disk/basic/distros/ubuntu_14.04.yaml
* ceph-disk/basic/tasks/ceph-disk.yaml

(which would of course be wrong in this case).

Referring to the `ceph/qa sub-directory`_, you will notice that the
``centos_7.0.yaml`` and ``ubuntu_14.04.yaml`` files in the
``suites/ceph-disk/basic/distros/`` directory are implemented as symlinks.
By using symlinks instead of copying, a single file can appear in multiple
suites. This eases the maintenance of the test framework as a whole.

All the tests generated from the ``suites/ceph-disk/`` directory tree
(also known as the "ceph-disk suite") can be run with::

  $ teuthology-suite --suite ceph-disk

An individual test from the `ceph-disk suite`_ can be run by adding the
``--filter`` option::

  $ teuthology-suite \
      --suite ceph-disk/basic \
      --filter 'ceph-disk/basic/{distros/ubuntu_14.04.yaml tasks/ceph-disk.yaml}'

.. note: To run a standalone test like the one in `Reading a standalone
   test`_, ``--suite`` alone is sufficient. If you want to run a single
   test from a suite that is defined as a directory tree, ``--suite`` must
   be combined with ``--filter``. This is because the ``--suite`` option
   understands POSIX relative paths only.

Concatenation operator
----------------------

For even greater flexibility in sharing yaml files between suites, the
special file plus (``+``) can be used to concatenate files within a
directory. For instance, consider the `suites/rbd/thrash
<https://github.com/ceph/ceph/tree/master/qa/suites/rbd/thrash>`_
tree::

  directory: rbd/thrash
    file: %
    directory: clusters
      file: +
      file: fixed-2.yaml
      file: openstack.yaml
    directory: workloads
      file: rbd_api_tests_copy_on_read.yaml
      file: rbd_api_tests.yaml

This creates two tests:

* rbd/thrash/{clusters/fixed-2.yaml clusters/openstack.yaml workloads/rbd_api_tests_copy_on_read.yaml}
* rbd/thrash/{clusters/fixed-2.yaml clusters/openstack.yaml workloads/rbd_api_tests.yaml}

Because the ``clusters/`` subdirectory contains the special file plus
(``+``), all the other files in that subdirectory (``fixed-2.yaml`` and
``openstack.yaml`` in this case) are concatenated together
and treated as a single file. Without the special file plus, they would
have been convolved with the files from the workloads directory to create
a 2x2 matrix:

* rbd/thrash/{clusters/openstack.yaml workloads/rbd_api_tests_copy_on_read.yaml}
* rbd/thrash/{clusters/openstack.yaml workloads/rbd_api_tests.yaml}
* rbd/thrash/{clusters/fixed-2.yaml workloads/rbd_api_tests_copy_on_read.yaml}
* rbd/thrash/{clusters/fixed-2.yaml workloads/rbd_api_tests.yaml}

The ``clusters/fixed-2.yaml`` file is shared among many suites to
define the following ``roles``::

  roles:
  - [mon.a, mon.c, osd.0, osd.1, osd.2, client.0]
  - [mon.b, osd.3, osd.4, osd.5, client.1]

The ``rbd/thrash`` suite as defined above, consisting of two tests, 
can be run with::

  $ teuthology-suite --suite rbd/thrash

A single test from the rbd/thrash suite can be run by adding the
``--filter`` option::

  $ teuthology-suite \
      --suite rbd/thrash \
      --filter 'rbd/thrash/{clusters/fixed-2.yaml clusters/openstack.yaml workloads/rbd_api_tests_copy_on_read.yaml}'

Filtering tests by their description
------------------------------------

When a few jobs fail and need to be run again, the ``--filter`` option
can be used to select tests with a matching description. For instance, if the
``rados`` suite fails the `all/peer.yaml <https://github.com/ceph/ceph/blob/master/qa/suites/rados/singleton/all/peer.yaml>`_ test, the following will only run the tests that contain this file::

  teuthology-suite --suite rados --filter all/peer.yaml

The ``--filter-out`` option does the opposite (it matches tests that do
`not` contain a given string), and can be combined with the ``--filter``
option.

Both ``--filter`` and ``--filter-out`` take a comma-separated list of strings (which
means the comma character is implicitly forbidden in filenames found in the
`ceph/qa sub-directory`_). For instance::

  teuthology-suite --suite rados --filter all/peer.yaml,all/rest-api.yaml

will run tests that contain either
`all/peer.yaml <https://github.com/ceph/ceph/blob/master/qa/suites/rados/singleton/all/peer.yaml>`_
or
`all/rest-api.yaml <https://github.com/ceph/ceph/blob/master/qa/suites/rados/singleton/all/rest-api.yaml>`_

Each string is looked up anywhere in the test description and has to
be an exact match: they are not regular expressions.

Reducing the number of tests
----------------------------

The ``rados`` suite generates thousands of tests out of a few hundred
files. This happens because teuthology constructs test matrices from
subdirectories wherever it encounters a file named ``%``. For instance,
all tests in the `rados/basic suite
<https://github.com/ceph/ceph/tree/master/qa/suites/rados/basic>`_
run with different messenger types: ``simple``, ``async`` and
``random``, because they are combined (via the special file ``%``) with
the `msgr directory
<https://github.com/ceph/ceph/tree/master/qa/suites/rados/basic/msgr>`_

All integration tests are required to be run before a Ceph release is published. 
When merely verifying whether a contribution can be merged without
risking a trivial regression, it is enough to run a subset. The ``--subset`` option can be used to
reduce the number of tests that are triggered. For instance::

  teuthology-suite --suite rados --subset 0/4000

will run as few tests as possible. The tradeoff in this case is that
some tests will only run on ``xfs`` and not on ``ext4`` or ``btrfs``,
but no matter how small a ratio is provided in the ``--subset``,
teuthology will still ensure that all files in the suite are in at
least one test. Understanding the actual logic that drives this
requires reading the teuthology source code.

The ``--limit`` option only runs the first ``N`` tests in the suite:
this is rarely useful, however, because there is no way to control which
test will be first.

Testing in the cloud
====================

In this chapter, we will explain in detail how use an OpenStack
tenant as an environment for Ceph integration testing.

Assumptions and caveat
----------------------

We assume that:

1. you are the only person using the tenant
2. you have the credentials
3. the tenant supports the ``nova`` and ``cinder`` APIs

Caveat: be aware that, as of this writing (July 2016), testing in
OpenStack clouds is a new feature. Things may not work as advertised.
If you run into trouble, ask for help on `IRC`_ or the `Mailing list`_, or
open a bug report at the `ceph-workbench bug tracker`_.

.. _`ceph-workbench bug tracker`: http://ceph-workbench.dachary.org/root/ceph-workbench/issues

Prepare tenant
--------------

If you have not tried to use ``ceph-workbench`` with this tenant before,
proceed to the next step.

To start with a clean slate, login to your tenant via the Horizon dashboard and:

* terminate the ``teuthology`` and ``packages-repository`` instances, if any
* delete the ``teuthology`` and ``teuthology-worker`` security groups, if any
* delete the ``teuthology`` and ``teuthology-myself`` key pairs, if any

Also do the above if you ever get key-related errors ("invalid key", etc.) when
trying to schedule suites.

Getting ceph-workbench
----------------------

Since testing in the cloud is done using the `ceph-workbench
ceph-qa-suite`_ tool, you will need to install that first. It is designed
to be installed via Docker, so if you don't have Docker running on your
development machine, take care of that first. You can follow `the official
tutorial<https://docs.docker.com/engine/installation/>`_ to install if
you have not installed yet.

Once Docker is up and running, install ``ceph-workbench`` by following the
`Installation instructions in the ceph-workbench documentation
<http://ceph-workbench.readthedocs.org/en/latest/#installation>`_.

Linking ceph-workbench with your OpenStack tenant
-------------------------------------------------

Before you can trigger your first teuthology suite, you will need to link
``ceph-workbench`` with your OpenStack account. 

First, download a ``openrc.sh`` file by clicking on the "Download OpenStack
RC File" button, which can be found in the "API Access" tab of the "Access
& Security" dialog of the OpenStack Horizon dashboard.

Second, create a ``~/.ceph-workbench`` directory, set its permissions to
700, and move the ``openrc.sh`` file into it. Make sure that the filename
is exactly ``~/.ceph-workbench/openrc.sh``.

Third, edit the file so it does not ask for your OpenStack password
interactively. Comment out the relevant lines and replace them with
something like::

    export OS_PASSWORD="aiVeth0aejee3eep8rogho3eep7Pha6ek"

When `ceph-workbench ceph-qa-suite`_ connects to your OpenStack tenant for
the first time, it will generate two keypairs: ``teuthology-myself`` and
``teuthology``. 

.. If this is not the first time you have tried to use
.. `ceph-workbench ceph-qa-suite`_ with this tenant, make sure to delete any
.. stale keypairs with these names!

Run the dummy suite
-------------------

You are now ready to take your OpenStack teuthology setup for a test
drive::

    $ ceph-workbench ceph-qa-suite --suite dummy

Be forewarned that the first run of `ceph-workbench ceph-qa-suite`_ on a
pristine tenant will take a long time to complete because it downloads a VM
image and during this time the command may not produce any output. 

The images are cached in OpenStack, so they are only downloaded once.
Subsequent runs of the same command will complete faster.

Although ``dummy`` suite does not run any tests, in all other respects it
behaves just like a teuthology suite and produces some of the same
artifacts.

The last bit of output should look something like this::

  pulpito web interface: http://149.202.168.201:8081/
  ssh access           : ssh -i /home/smithfarm/.ceph-workbench/teuthology-myself.pem ubuntu@149.202.168.201 # logs in /usr/share/nginx/html

What this means is that `ceph-workbench ceph-qa-suite`_ triggered the test
suite run. It does not mean that the suite run has completed. To monitor
progress of the run, check the Pulpito web interface URL periodically, or
if you are impatient, ssh to the teuthology machine using the ssh command
shown and do::

    $ tail -f /var/log/teuthology.*

The `/usr/share/nginx/html` directory contains the complete logs of the
test suite. If we had provided the ``--upload`` option to the
`ceph-workbench ceph-qa-suite`_ command, these logs would have been
uploaded to http://teuthology-logs.public.ceph.com.

Run a standalone test
---------------------

The standalone test explained in `Reading a standalone test`_ can be run
with the following command::

    $ ceph-workbench ceph-qa-suite --suite rados/singleton/all/admin-socket.yaml

This will run the suite shown on the current ``master`` branch of
``ceph/ceph.git``. You can specify a different branch with the ``--ceph``
option, and even a different git repo with the ``--ceph-git-url`` option. (Run
``ceph-workbench ceph-qa-suite --help`` for an up-to-date list of available
options.)

The first run of a suite will also take a long time, because ceph packages
have to be built, first. Again, the packages so built are cached and
`ceph-workbench ceph-qa-suite`_ will not build identical packages a second
time.

Interrupt a running suite
-------------------------

Teuthology suites take time to run. From time to time one may wish to
interrupt a running suite. One obvious way to do this is::

    ceph-workbench ceph-qa-suite --teardown

This destroys all VMs created by `ceph-workbench ceph-qa-suite`_ and
returns the OpenStack tenant to a "clean slate".

Sometimes you may wish to interrupt the running suite, but keep the logs,
the teuthology VM, the packages-repository VM, etc. To do this, you can
``ssh`` to the teuthology VM (using the ``ssh access`` command reported
when you triggered the suite -- see `Run the dummy suite`_) and, once
there::

    sudo /etc/init.d/teuthology restart

This will keep the teuthology machine, the logs and the packages-repository
instance but nuke everything else.

Upload logs to archive server
-----------------------------

Since the teuthology instance in OpenStack is only semi-permanent, with limited
space for storing logs, ``teuthology-openstack`` provides an ``--upload``
option which, if included in the ``ceph-workbench ceph-qa-suite`` command,
will cause logs from all failed jobs to be uploaded to the log archive server
maintained by the Ceph project. The logs will appear at the URL::

    http://teuthology-logs.public.ceph.com/$RUN

where ``$RUN`` is the name of the run. It will be a string like this::

    ubuntu-2016-07-23_16:08:12-rados-hammer-backports---basic-openstack

Even if you don't providing the ``--upload`` option, however, all the logs can
still be found on the teuthology machine in the directory
``/usr/share/nginx/html``.

Provision VMs ad hoc
--------------------

From the teuthology VM, it is possible to provision machines on an "ad hoc"
basis, to use however you like. The magic incantation is::

    teuthology-lock --lock-many $NUMBER_OF_MACHINES \
        --os-type $OPERATING_SYSTEM \
        --os-version $OS_VERSION \
        --machine-type openstack \
        --owner $EMAIL_ADDRESS

The command must be issued from the ``~/teuthology`` directory. The possible
values for ``OPERATING_SYSTEM`` AND ``OS_VERSION`` can be found by examining
the contents of the directory ``teuthology/openstack/``. For example::

    teuthology-lock --lock-many 1 --os-type ubuntu --os-version 16.04 \
        --machine-type openstack --owner foo@example.com

When you are finished with the machine, find it in the list of machines::

    openstack server list

to determine the name or ID, and then terminate it with::

    openstack server delete $NAME_OR_ID

Deploy a cluster for manual testing
-----------------------------------

The `teuthology framework`_ and `ceph-workbench ceph-qa-suite`_ are 
versatile tools that automatically provision Ceph clusters in the cloud and
run various tests on them in an automated fashion. This enables a single
engineer, in a matter of hours, to perform thousands of tests that would
keep dozens of human testers occupied for days or weeks if conducted
manually.

However, there are times when the automated tests do not cover a particular
scenario and manual testing is desired. It turns out that it is simple to
adapt a test to stop and wait after the Ceph installation phase, and the
engineer can then ssh into the running cluster. Simply add the following
snippet in the desired place within the test YAML and schedule a run with the
test::

    tasks:
    - exec:
        client.0:
          - sleep 1000000000 # forever

(Make sure you have a ``client.0`` defined in your ``roles`` stanza or adapt
accordingly.)

The same effect can be achieved using the ``interactive`` task::

    tasks:
    - interactive

By following the test log, you can determine when the test cluster has entered
the "sleep forever" condition. At that point, you can ssh to the teuthology
machine and from there to one of the target VMs (OpenStack) or teuthology
worker machines machine (Sepia) where the test cluster is running.

The VMs (or "instances" in OpenStack terminology) created by
`ceph-workbench ceph-qa-suite`_ are named as follows:

``teuthology`` - the teuthology machine

``packages-repository`` - VM where packages are stored

``ceph-*`` - VM where packages are built

``target*`` - machines where tests are run

The VMs named ``target*`` are used by tests. If you are monitoring the
teuthology log for a given test, the hostnames of these target machines can
be found out by searching for the string ``Locked targets``::

    2016-03-20T11:39:06.166 INFO:teuthology.task.internal:Locked targets:
      target149202171058.teuthology: null
      target149202171059.teuthology: null

The IP addresses of the target machines can be found by running ``openstack
server list`` on the teuthology machine, but the target VM hostnames (e.g.
``target149202171058.teuthology``) are resolvable within the teuthology
cluster.


Testing - how to run s3-tests locally
=====================================

RGW code can be tested by building Ceph locally from source, starting a vstart
cluster, and running the "s3-tests" suite against it.

The following instructions should work on jewel and above.

Step 1 - build Ceph
-------------------

Refer to :doc:`install/build-ceph`.

You can do step 2 separately while it is building.

Step 2 - vstart
---------------

When the build completes, and still in the top-level directory of the git
clone where you built Ceph, do the following, for cmake builds::

    cd build/
    RGW=1 ../vstart.sh -n

This will produce a lot of output as the vstart cluster is started up. At the
end you should see a message like::

    started.  stop.sh to stop.  see out/* (e.g. 'tail -f out/????') for debug output.

This means the cluster is running.


Step 3 - run s3-tests
---------------------

To run the s3tests suite do the following::

   $ ../qa/workunits/rgw/run-s3tests.sh

.. WIP
.. ===
..
.. Building RPM packages
.. ---------------------
..
.. Ceph is regularly built and packaged for a number of major Linux
.. distributions. At the time of this writing, these included CentOS, Debian,
.. Fedora, openSUSE, and Ubuntu.
..
.. Architecture
.. ============
.. 
.. Ceph is a collection of components built on top of RADOS and provide
.. services (RBD, RGW, CephFS) and APIs (S3, Swift, POSIX) for the user to
.. store and retrieve data.
.. 
.. See :doc:`/architecture` for an overview of Ceph architecture. The
.. following sections treat each of the major architectural components
.. in more detail, with links to code and tests.
.. 
.. FIXME The following are just stubs. These need to be developed into
.. detailed descriptions of the various high-level components (RADOS, RGW,
.. etc.) with breakdowns of their respective subcomponents.
.. 
.. FIXME Later, in the Testing chapter I would like to take another look
.. at these components/subcomponents with a focus on how they are tested.
.. 
.. RADOS
.. -----
.. 
.. RADOS stands for "Reliable, Autonomic Distributed Object Store". In a Ceph
.. cluster, all data are stored in objects, and RADOS is the component responsible
.. for that.
.. 
.. RADOS itself can be further broken down into Monitors, Object Storage Daemons
.. (OSDs), and client APIs (librados). Monitors and OSDs are introduced at
.. :doc:`/start/intro`. The client library is explained at
.. :doc:`/rados/api/index`.
.. 
.. RGW
.. ---
.. 
.. RGW stands for RADOS Gateway. Using the embedded HTTP server civetweb_ or
.. Apache FastCGI, RGW provides a REST interface to RADOS objects.
.. 
.. .. _civetweb: https://github.com/civetweb/civetweb
.. 
.. A more thorough introduction to RGW can be found at :doc:`/radosgw/index`.
.. 
.. RBD
.. ---
.. 
.. RBD stands for RADOS Block Device. It enables a Ceph cluster to store disk
.. images, and includes in-kernel code enabling RBD images to be mounted.
.. 
.. To delve further into RBD, see :doc:`/rbd/rbd`.
.. 
.. CephFS
.. ------
.. 
.. CephFS is a distributed file system that enables a Ceph cluster to be used as a NAS.
.. 
.. File system metadata is managed by Meta Data Server (MDS) daemons. The Ceph
.. file system is explained in more detail at :doc:`/cephfs/index`.
..