Multiple MailerQ instances on a single server.
You can run multiple MailerQ instances on a single server. But it does require some extra work.
If you run multiple instances on the same machine, these instances will still all load their configuration from the central /etc/mailerq/config.txt config file. This is no problem for most of the settings, but some specific settings need to different for each instance. For example, the different instances all need a seperate lock file, and have to use different port numbers to listen to.
Seperate config file
If you want to run multiple instances at the same time, you still need to create a central /etc/mailerq/config.txt file with MailerQ's configuration. This file contain the settings that apply to all instances. But besides this central config file, you also need additional config files (for example /etc/mailerq/instance-1.txt, /etc/mailerq/instance-2.txt, et cetera) for the individual instances. In these config file you put the instance-specific settings.
If you start a MailerQ instance, you have to use the
line option to specify the configuration file to use:
mailerq --config-file /etc/mailerq/instance-2.txt
With the above command you start a MailerQ process that loads both the normal /etc/mailerq/config.txt file, as well as the additional /etc/mailerq/instance-2.txt file.
When MailerQ starts, the settings are loaded in the following order:
1. Hardcoded default settings 2. Default config file (/etc/mailerq/config.txt) 3. Config file set in --config-file argument (optional) 4. Command line arguments (optional)
To simplify the configuration files, you can use the default config file for all the shared settings and instance specific files with just the unique options.
Unique settings per instance
There are a couple of settings that almost always must be unique if you run more than once instance:
- outbox queues
- listening IP/port combinations
- log files location
- lock file
- server ID
The outbox queue must be unique per instance to manage which messages are sent by which MailerQ instance. Port number are limited resources and it is normally not possible to have multiple processes that all listen to the same port number. These settings have to be unique too:
rabbitmq-outbox: outbox1 smtp-ip: 10.0.0.1 www-ip: 10.0.0.1 www-host: mta001.example.com
Log files location
To avoid corruption (you don't want that different processes write to the same log file at the same time) it is advised to use separate log files or log directories for the instances. If you choose to use different directories, make sure to create then and change ownership to the MailerQ user.
This is an example if you use different directories:
error-log: /var/log/mailerq/instance1/errors.log send-log-directory: /var/log/mailerq/instance1/ download-log-directory: /var/log/mailerq/instance1/ received-log-directory: /var/log/mailerq/instance1/
This is an example if you use different prefixes:
error-log: /var/log/mailerq/instance1-errors.log send-log-prefix: instance1-attemtps.log download-log-prefix: instance1-downloads.log received-log-prefix: instance1-received.log
To prevent a MailerQ instance from starting more than once, MailerQ stores its process ID (pid) in a lockfile. This must be unique for every instance:
Each message that is accepted by MailerQ gets a unique message ID. To prevent that multiple instances assign exactly the same ID to a message, you can assign a "server-id" variable. This identifier guarantees that message ID's never conflict.
We recommend to enable the clustering when running multiple MailerQ instances. Because when changes are applied in one web interface, they are also immediately applied to all instances in a cluster. To enable clustering set the following options in the default configuration file:
cluster-address: amqp://user:firstname.lastname@example.org/ cluster-exchange: cluster
If you like to use init scripts to start multiple MailerQ instances, you can copy the default init script:
$ sudo cp /etc/init.d/mailerq /etc/init.d/mailerq-instance1
and alter the following settings inside the copied file (/etc/init.d/mailerq-instance1):
NAME="mailerq-instance1" DESC="MailerQ daemon instance1" PIDFILE="/tmp/mailerq-instance1.pid" DAEMON="/usr/bin/mailerq --config-file /etc/mailerq/instance1.txt"
Now you can start your instances from the terminal like:
$ sudo service mailerq-instance1 start
$ sudo systemctl start mailerq-instance1
Process supervisor (monit example) or cron
To keep instances running you can use a process supervisor like Monit. With our previous example, a simple Monit script for MailerQ instance looks like:
check process mailerq with pidfile /tmp/mailerq-instance1.pid group mail start program = "/etc/init.d/mailerq-instance1 start" stop program = "/etc/init.d/mailerq-instance1 stop" if failed host 10.0.0.1 port 25 protocol smtp then restart
Alternatively you can use cron to restart your MailerQ instances if they are not running. This can be set in the crontab for either the root or MailerQ user.
* * * * * kill -0 $(cat /tmp/mailerq-instance1.pid) || /usr/bin/mailerq --config-file /etc/mailerq/instance1.txt & * * * * * kill -0 $(cat /tmp/mailerq-instance2.pid) || /usr/bin/mailerq --config-file /etc/mailerq/instance2.txt &
Example config files
An example of two configuration files for different instances:
rabbitmq-outbox: outbox1 rabbitmq-inbox: outbox1 smtp-ip: 10.0.0.1 www-ip: 10.0.0.1 www-host: mta001.example.com error-log: /var/log/mailerq/instance1-errors.log send-log-prefix: instance1-attempts.log download-log-prefix: instance1-downloads.log received-log-prefix: instance1-received.log lock: /tmp/mailerq-instance1.pid server-id: 1
rabbitmq-outbox: outbox2 rabbitmq-inbox: outbox2 smtp-ip: 10.0.0.2 www-ip: 10.0.0.2 www-host: mta002.example.com error-log: /var/log/mailerq/instance2-errors.log send-log-prefix: instance2-attempts.log download-log-prefix: instance2-downloads.log received-log-prefix: instance2-received.log lock: /tmp/mailerq-instance2.pid server-id: 2