:pmg-toplevel:
endif::manvolnum[]
-We are living in a world where email becomes more and more important -
-failures in email systems are just not acceptable. To meet these
-requirements we developed the Proxmox HA (High Availability) Cluster.
+We are living in a world where email is becoming more and more important -
+failures in email systems are not acceptable. To meet these
+requirements, we developed the Proxmox HA (High Availability) Cluster.
-The {pmg} HA Cluster consists of a master and several slave nodes
-(minimum one node). Configuration is done on the master. Configuration
-and data is synchronized to all cluster nodes over a VPN tunnel. This
+The {pmg} HA Cluster consists of a master node and several slave nodes
+(minimum one slave node). Configuration is done on the master,
+and data is synchronized to all cluster nodes via a VPN tunnel. This
provides the following advantages:
* centralized configuration management
* high performance
We use a unique application level clustering scheme, which provides
-extremely good performance. Special considerations where taken to make
-management as easy as possible. Complete Cluster setup is done within
-minutes, and nodes automatically reintegrate after temporary failures
+extremely good performance. Special considerations were taken to make
+management as easy as possible. A complete cluster setup is done within
+minutes, and nodes automatically reintegrate after temporary failures,
without any operator interaction.
image::images/Proxmox_HA_cluster_final_1024.png[]
-Hardware requirements
+Hardware Requirements
---------------------
There are no special hardware requirements, although it is highly
-recommended to use fast and reliable server with redundant disks on
+recommended to use fast and reliable server hardware, with redundant disks on
all cluster nodes (Hardware RAID with BBU and write cache enabled).
The HA Cluster can also run in virtualized environments.
Subscriptions
-------------
-Each host in a cluster has its own subscription. If you want support
+Each node in a cluster has its own subscription. If you want support
for a cluster, each cluster node needs to have a valid
subscription. All nodes must have the same subscription level.
-Load balancing
+Load Balancing
--------------
It is usually advisable to distribute mail traffic among all cluster
nodes. Please note that this is not always required, because it is
also reasonable to use only one node to handle SMTP traffic. The
-second node is used as quarantine host, and only provides the web
+second node can then be used as a quarantine host, that only provides the web
interface to the user quarantine.
The normal mail delivery process looks up DNS Mail Exchange (`MX`)
-records to determine the destination host. A `MX` record tells the
+records to determine the destination host. An `MX` record tells the
sending system where to deliver mail for a certain domain. It is also
-possible to have several `MX` records for a single domain, they can have
-different priorities. For example, our `MX` record looks like that:
+possible to have several `MX` records for a single domain, each of which can
+have different priorities. For example, our `MX` record looks like this:
----
# dig -t mx proxmox.com
mail.proxmox.com. 22879 IN A 213.129.239.114
----
-Please notice that there is one single `MX` record for the Domain
+Notice that there is a single `MX` record for the domain
`proxmox.com`, pointing to `mail.proxmox.com`. The `dig` command
-automatically puts out the corresponding address record if it
+automatically outputs the corresponding address record, if it
exists. In our case it points to `213.129.239.114`. The priority of
our `MX` record is set to 10 (preferred default value).
Hot standby with backup `MX` records
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Many people do not want to install two redundant mail proxies, instead
-they use the mail proxy of their ISP as fallback. This is simply done
-by adding an additional `MX` Record with a lower priority (higher
-number). With the example above this looks like that:
+Many people do not want to install two redundant mail proxies. Instead
+they use the mail proxy of their ISP as a fallback. This can be done
+by adding an additional `MX` record with a lower priority (higher
+number). Continuing from the example above, this would look like:
----
proxmox.com. 22879 IN MX 100 mail.provider.tld.
In such a setup, your provider must accept mails for your domain and
forward them to you. Please note that this is not advisable, because
spam detection needs to be done by the backup `MX` server as well, and
-external servers provided by ISPs usually don't.
+external servers provided by ISPs usually don't do this.
However, you will never lose mails with such a setup, because the sending Mail
Transport Agent (MTA) will simply deliver the mail to the backup
-server (mail.provider.tld) if the primary server (mail.proxmox.com) is
+server (mail.provider.tld), if the primary server (mail.proxmox.com) is
not available.
NOTE: Any reasonable mail server retries mail delivery if the target
-server is not available, i.e. {pmg} stores mail and retries delivery
-for up to one week. So you will not lose mail if your mail server is
+server is not available. {pmg} stores mail and retries delivery
+for up to one week. Thus, you will not lose emails if your mail server is
down, even if you run a single server setup.
Load balancing with `MX` records
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Using your ISPs mail server is not always a good idea, because many
+Using your ISP's mail server is not always a good idea, because many
ISPs do not use advanced spam prevention techniques, or do not filter
-SPAM at all. It is often better to run a second server yourself to
+spam at all. It is often better to run a second server yourself to
avoid lower spam detection rates.
-Anyways, it’s quite simple to set up a high performance load balanced
-mail cluster using `MX` records. You just need to define two `MX` records
-with the same priority. Here is a complete example to make it clearer.
+It’s quite simple to set up a high-performance, load-balanced
+mail cluster using `MX` records. You just need to define two `MX`
+records with the same priority. The rest of this section will provide
+a complete example.
-First, you need to have at least 2 working {pmg} servers
-(mail1.example.com and mail2.example.com) configured as cluster (see
-section xref:pmg_cluster_administration[Cluster administration]
-below), each having its own IP address. Let us assume the following
-addresses (DNS address records):
+First, you need to have at least two working {pmg} servers
+(mail1.example.com and mail2.example.com), configured as a cluster (see
+section xref:pmg_cluster_administration[Cluster Administration]
+below), with each having its own IP address. Let us assume the
+following DNS address records:
----
mail1.example.com. 22879 IN A 1.2.3.4
----
It is always a good idea to add reverse lookup entries (PTR
-records) for those hosts. Many email systems nowadays reject mails
-from hosts without valid PTR records. Then you need to define your `MX`
+records) for those hosts, as many email systems nowadays reject mails
+from hosts without valid PTR records. Then you need to define your `MX`
records:
----
example.com. 22879 IN MX 10 mail2.example.com.
----
-This is all you need. You will receive mails on both hosts, more or
-less load-balanced using round-robin scheduling. If one host fails the
-other one is used.
+This is all you need. Following this, you will receive mail on both
+hosts, load-balanced using round-robin scheduling. If one host fails,
+the other one is used.
Other ways
Multiple address records
^^^^^^^^^^^^^^^^^^^^^^^^
-Using several DNS `MX` records is sometimes clumsy if you have many
+Using several DNS `MX` records can be tedious, if you have many
domains. It is also possible to use one `MX` record per domain, but
multiple address records:
[[pmg_cluster_administration]]
-Cluster administration
+Cluster Administration
----------------------
-Cluster administration can be done on the GUI or using the command
-line utility `pmgcm`. The CLI tool is a bit more verbose, so we suggest
-to use that if you run into problems.
+Cluster administration can be done from the GUI or by using the command-line
+utility `pmgcm`. The CLI tool is a bit more verbose, so we suggest
+to use that if you run into any problems.
-NOTE: Always setup the IP configuration before adding a node to the
+NOTE: Always set up the IP configuration, before adding a node to the
cluster. IP address, network mask, gateway address and hostname can’t
be changed later.
Creating a Cluster
~~~~~~~~~~~~~~~~~~
-[thumbnail="pmg-gui-cluster-panel.png", big=1]
+[thumbnail="screenshot/pmg-gui-cluster-panel.png", big=1]
You can create a cluster from any existing {pmg} host. All data is
preserved.
Show Cluster Status
~~~~~~~~~~~~~~~~~~~
-The GUI shows the status of all cluster nodes, and it is also possible
-to use the command line tool:
+The GUI shows the status of all cluster nodes. You can also view this
+using the command-line tool:
----
pmgcm status
Adding Cluster Nodes
~~~~~~~~~~~~~~~~~~~~
-[thumbnail="pmg-gui-cluster-join.png", big=1]
+[thumbnail="screenshot/pmg-gui-cluster-join.png", big=1]
-When you add a new node to a cluster (using `join`) all data on that node is
-destroyed. The whole database is initialized with cluster data from
+When you add a new node to a cluster (using `join`), all data on that node is
+destroyed. The whole database is initialized with the cluster data from
the master.
* make sure you have the right IP configuration
pmgcm join <master_ip>
----
-You need to enter the root password of the master host when asked for
+You need to enter the root password of the master host, when asked for
a password. When joining a cluster using the GUI, you also need to
-enter the 'fingerprint' of the master node. You get that information
+enter the 'fingerprint' of the master node. You can get this information
by pressing the `Add` button on the master node.
-CAUTION: Node initialization deletes all existing databases, stops and
-then restarts all services accessing the database. So do not add nodes
-which are already active and receive mails.
+NOTE: Joining a cluster with two-factor authentication enabled for the `root`
+user is not supported. Remove the second factor when joining the cluster.
-Also, joining a cluster can take several minutes, because the new node
-needs to synchronize all data from the master (although this is done
-in the background).
+CAUTION: Node initialization deletes all existing databases, stops all
+services accessing the database and then restarts them. Therefore, do
+not add nodes which are already active and receive mail.
-NOTE: If you join a new node, existing quarantined items from the other nodes are not synchronized to the new node.
+Also note that joining a cluster can take several minutes, because the
+new node needs to synchronize all data from the master (although this
+is done in the background).
+
+NOTE: If you join a new node, existing quarantined items from the
+other nodes are not synchronized to the new node.
Deleting Nodes
~~~~~~~~~~~~~~
-Please detach nodes from the cluster network before removing them
-from the cluster configuration. Then run the following command on
-the master node:
+Please detach nodes from the cluster network, before removing them
+from the cluster configuration. Only then you should run the following
+command on the master node:
----
pmgcm delete <cid>
~~~~~~~~~~~~~~~~~
It is highly recommended to use redundant disks on all cluster nodes
-(RAID). So in almost any circumstances you just need to replace the
+(RAID). So in almost any circumstance, you just need to replace the
damaged hardware or disk. {pmg} uses an asynchronous
clustering algorithm, so you just need to reboot the repaired node,
and everything will work again transparently.
Total Cluster Failure
^^^^^^^^^^^^^^^^^^^^^
-* restore backup (Cluster and node information is not restored, you
+* restore backup (Cluster and node information is not restored; you
have to recreate master and nodes)
* tell it to become master
projects / pmg-docs.git / blobdiff