DNS Auto Scaling

[niklas88]

This issue mostly serves as a note. The current varnish configuration is kept minimal. In particular it does not support multi DNS based auto scaling. Meaning if you use docker-compose up -d --scale virtuoso=2 or similar, varnish will not use both backends.

This is because the support for round-robin scheduling among multiple DNS entries is a premium feature of varnish+. One can work around this with extra scripts and triggering a reload as done e.g. in this docker image but that adds significant complexity or new external dependencies. So for now only one backend instance is supported.