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rsyslog

Docker image running rsyslog.

How it works

I started off with jpetazzo's syslogdocker, but didn't want to do the explicit host bind-mount to avoid sharing /dev. To solve that, I make rsyslog create the socket in /var/run/rsyslog/dev/log instead of the default location at /dev/log. This allows me to do --volumes-from without conflict, by making a symbolic link from /dev/log to the socket in the shared volume.

Another improvement is that I wanted to do docker logs syslog to see my logs, instead of a docker exec -t syslog tail -f /var/log/syslog. To do that, I've included an example configuration file that catches all priorities from LEVEL1 facility and send them to stderr:

# /etc/rsyslog.d/20-user.conf

local1.*  {
    /proc/self/fd/2
    stop
}

How to use?

First, start the rsyslog container:

docker run -d --name syslog helder/rsyslog

1. Symlink to /dev/log

If you must use /dev/log, you can start any container that you want to log to syslog with:

docker run -it --rm --volumes-from syslog debian:jessie bash -c "ln -sf /var/run/rsyslog/dev/log /dev/log && logger -p local1.notice This is a notice!"

Obviously you'd create the symlink in the Dockerfile, or an entrypoint.

2. Use the custom socket location directly

If you can send your logs to any socket, then you don't need the symlink:

docker run -it --rm --volumes-from syslog debian:jessie logger -u /var/run/rsyslog/dev/log -t myapp -p local1.error This is an error!

3. Use a remote tcp connection

If you can send your logs to a remote host, use port 514:

docker run -it --rm --link syslog debian:jessie logger -n syslog -T -P 514 -p local1.error This is a remote error!

4. Use socat to connect local socket to remote host

Something like (not tested):

socat UNIX-LISTEN:/dev/log,reuseaddr,fork TCP:syslog:514

Add configuration

Just create your config files and in your Dockerfile, copy them to /etc/rsyslog.d/.

Read logs

Assuming you're using LEVEL1 priority, or added your own config to send logs to stderr or stdout, your logs can be seen with:

docker logs -f syslog
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