Icinga in Docker: which eMail client to use for notifications?

Al2Klimov · January 14, 2021, 5:50pm

Hi there!

@mcktr requested the ability to send notifications via eMail from our Icinga 2 Docker image. There’s one problem: the container runs only Icinga 2, so even if one wouldn’t use a public MTA, but a local one, it would be an extra container – and over the network anyway.

As I’m not very familiar with server MUAs, so I need your help: What program you’d expect behind mail in the container and why exactly? Requirements:

Non-127.0.0.0/8 MTA can be specified easily, preferably via a mounted .PROGRAMNAMErc or env vars (may be specified at Docker level as Icinga 2 passes its own env to subprocesses)
These ones have to still work

Best,
AK

dgoetz · January 14, 2021, 9:04pm

What you would need here is a sendmail compatible solution that directly sends to a mail relay instead of the local mta. I have no preference here, but I have seen esmtp, ssmtp and nullmailer in action in different environments. I would investigate which one is easiest to install and configure so passing config to the container is as simply as possible, but there could also be other things to consider.

mcktr · February 22, 2021, 12:35pm

Hi,

I just saw that postfix is installed in the container.

github.com

Icinga/docker-icinga2/blob/68036a12182f7e7c047a9fd67714187bcb263169/deps.Dockerfile#L62


RUN cd /check_postgres ;\
	mkdir bin ;\
	perl Makefile.PL INSTALLSITESCRIPT=/usr/lib/nagios/plugins ;\
	make ;\
	make install "DESTDIR=$(pwd)/bin"
FROM debian:buster-slim
RUN ["/bin/bash", "-exo", "pipefail", "-c", "export DEBIAN_FRONTEND=noninteractive; apt-get update; apt-get install --no-install-{recommends,suggests} -y dumb-init libboost-{context,coroutine,date-time,filesystem,program-options,regex,system,thread}1.67 libedit2 libmariadb3 libmoosex-role-timer-perl libpq5 libssl1.1 mailutils monitoring-plugins openssh-client openssl postfix; apt-get clean; rm -vrf /var/lib/apt/lists/*"]
COPY --from=entrypoint /entrypoint/entrypoint /entrypoint
RUN ["adduser", "--system", "--group", "--home", "/var/lib/icinga2", "--disabled-login", "--force-badname", "--no-create-home", "--uid", "5665", "icinga"]
COPY --from=build /check_mssql_health/bin/ /
COPY --from=build /check_nwc_health/bin/ /
COPY --from=build /check_postgres/bin/ /
COPY --from=clone /check_ssl_cert/check_ssl_cert /usr/lib/nagios/plugins/check_ssl_cert

But for my understanding the postfix daemon is not usable since the container runs only one process: the Icinga 2 daemon, correct?

For me ssmtp or. msmtp looks promising, no running daemon is needed.

(german blog post)

Unfortunately the ssmtp debian package is currently unmaintained, msmtp looks like an alternative.

Both provide a symlink for sendmail, so sending E-Mails using mail should work.

Best regards
Michael

Al2Klimov · February 4, 2021, 6:17pm

Unfortunately esmtp seems not to be maintained anymore, nullmailer seems to require a service and ssmtp seems not to be compatible with GNU mail which is expected by Icinga 2’s mail scripts. But thank you for the tips anyway!