poolmon health monitoring for dovecot director backends

This container wraps poolmon from Brandon Davidson to run alongside Dovecot director, e.g. as a sidecar in a Kubernetes pod.

Dovecot directors don't do backend health checking on their own. Instead, they timeout and fail if the request's target is unavailable. The Dovecot wiki points to poolmon which seems to be the most common way to go if you want to avoid a full load balancer setup.

Tags align with poolmon releases: 0.6, latest
Please open an issue or pull request on github if there is a new release I haven't noticed.

Configuration

For detail about the usage of poolmon, check out the help online or run docker run weised/dovecot-poolmon --help.

Use the following environment variables to configure the poolmon running inside this container.

Name	Default
DEBUG	``
DIRECTOR_SOCKET	/var/run/dovecot/director-admin
INTERVAL	30
LOGFILE	/dev/stdout
PORTS	--port=110 --port=143 --ssl=993 --ssl=995 --port=24
TIMEOUT	10
ADDITIONAL_OPTIONS	``

I chose to export only those options I deem common (aka those I am tweaking 🤓) but you can append any parameters to the ADDITIONAL_OPTIONS variable, e.g. ADDITIONAL_OPTIONS=--lockfile=/my/very/own/lockfile.pid.

Enable poolmon's debug log by setting DEBUG to a non-empty value.

The parameters --foreground and --logfile=/dev/stdout are always set and cannot be overwritten.

Running

• Mount your director's socket to /var/run/dovecot/director-admin (or any custom location you set using the DIRECTOR_SOCKET environment variable).
• Set above environment variables to your desired values.
• Set ADDITIONAL_OPTIONS to add additional parameters to poolmon.

Commandline

Start a container:
docker run -e INTERVAL=5 -v /var/run/dovecot/director-admin:/var/run/dovecot/director-admin weised/dovecot-poolmon

Runing the container like an executable might come handy in some situations:

• docker run -v /var/run/dovecot/director-admin:/var/run/dovecot/director-admin weised/dovecot-poolmon --timeout 5 --port IMAP:123
• docker run weised/dovecot-poolmon --help

Note: If you set any command line parameters, environment variables will be ignored.

docker-compose.yml

dovecot-poolmon:
  image: weised/dovecot-poolmon:latest
  restart: "always"
  environment:
    # Overwrite interval, check every ten years
    - POOLMON_INTERVAL=315360000
    # Add a port to check without overwriting the default ones
    - POOLMON_ADDITIONAL_OPTIONS=--port=POP3:4711
  volumes:
    - /var/run/dovecot/director-admin:/var/run/dovecot/director-admin

Building

You can easily build the container yourself:

git clone https://github.com/wedi/dovecot-poolmon-docker.git
cd dovecot-poolmon-docker
docker build -t dovecot-poolmon .

Optionally, choose the version of poolmon:
docker build --build-arg POOLMON_VERSION=master -t dovecot-poolmon .

License

Copyright © 2019 Dirk Weise <code-at-dirk-weise.de>
Released under the terms of the MIT License.