create docker builds for easy deployment

[pjstevns]

I would like the be able to use the smallest possible docker containers for deploying full-featured dbmail services in a docker swarm or k8s cluster.

I've started a docker branch, and have a poc working setup that still needs improvements:

• static binaries, no additional packages
• clear guidelines to ease deployments
• possibily add ENVIRONMENT of key-store (aws-parameters, etc) support to dbmail.conf to avoid hard coding config values.

[pjstevns]

Some updates:

• static binaries is a no-go. They are not really static after all, they just link the modules statically, not the required libraries (i.e. glib, gmime, zdb, mhash)
• running a daemon inside the container segfaults when running in stdin/out mode (-n). Network mode seems to work just fine (-D)
• the resulting images is now < 30MB, which is pretty nice!

[kak-tus]

Please, add this image as automated build at Docker Hub (with tags). It is simple.

I created and used image with dbmail for two years, but it is much bigger, than this alpine based.
https://hub.docker.com/r/kaktuss/dbmail

Also some notes to image:

1. It is better to declare not sh CMD to start some of dbmail binaries. May be with env variable (see example at my image) or may be with dedicated images for every binary.
2. It is better to start binaries as non privileged user. Something like this

RUN \
  adduser -DH user

USER user
CMD ...

3. I also had a problem with "-n" mode, but fixed it with running in "-D" mode and watching for pid
   https://github.com/kak-tus/docker-dbmail/blob/master/dbmail_start.sh#L24

[phozzy]

* static binaries is a no-go. They are not really static after all, they just link the modules statically, not the required libraries (i.e. glib, gmime, zdb, mhash)

-- that is actually ok. according to 12factorApp dependecies it is fine while you have explicit dependency specification.

* running a daemon inside the container segfaults when running in stdin/out mode (-n). Network mode seems to work just fine (-D)

-- sorry guys, I am not aware about dbmail internals, so I don't know how is it possible to run dbmail. But according to Configure app as PID 1 your application should run as PID1 inside a container, so not like a daemon.

* possibily add ENVIRONMENT of key-store (aws-parameters, etc) support to dbmail.conf to avoid hard coding config values.

-- according to 12factor App config it is strict requirement.

Just to mention :-)

[hemml]

I'm not sure it will be helpful here, but this is a script, which I'm using to build a deb package of latest dbmail:

docker rm dbmail-build
docker run --name dbmail-build debian:buster /bin/sh -c '
  apt-get update &&\
  apt-get -y dist-upgrade &&\
  apt-get -y install git automake automake1.11 autoconf debhelper\
          libncurses5-dev libldap2-dev libtool asciidoc xmlto po-debconf\
          default-libmysqlclient-dev libpq-dev libsqlite3-dev libsieve2-dev\
          libglib2.0-dev libgmime-2.6-dev libzdb-dev libmhash-dev libevent-dev\
          pkg-config libssl-dev cdbs libgmime-3.0-dev &&\
  mkdir /build-dir &&\
  cd /build-dir &&\
  git clone https://github.com/dbmail/dbmail.git &&\
  cd dbmail &&\
  dpkg-buildpackage -us -uc -d &&\
  cd /build-dir &&
  tar -cvf /dbmail.tar dbmail_*.deb' &&
docker cp dbmail-build:/dbmail.tar ./ &&
tar -xvf dbmail.tar &&
rm dbmail.tar &&
docker rm dbmail-build

(inspired by the instruction found here: http://innerlife.io/ru/dbmail-postgresql-postfix-sasl-debian-part2-2/)