Improve README for configuration changes, closes #47

[wohali]

Overview

README.md was misleading on the desired approach for making configuration changes, leading to PRs like #32. This makes it clearer that if you need more than you can get from a few simple env vars, you should be mounting /opt/couchdb/etc/local.d as a volume and persisting it to disk.

By specifying the local.d subdirectory we ensure that upstream image default changes to /opt/couchdb/etc/default.ini, as well as docker-specific upstream changes in /opt/couchdb/etc/default.d, are unaffected by externalisation of this volume.

Testing recommendations

Read it!

GitHub issue number

Closes #47

Checklist

• Documentation reflects the changes;

[wohali]

One weakness of this approach is that it means you cannot externalise /opt/couchdb/etc/vm.args.

I am torn on this point. There are parameters in there (like the erlang cookie) that would be good to persist.

However, externalising the entire /opt/couchdb/etc directory prevents us from slipstreaming changes to default.ini and default.d/* into the image successfully.

Perhaps we just add a new env var just for ERLANG_COOKIE and wipe our hands of it.

[chriswiggins]

The issue with not being able to expose vm.args is that there are other things that cannot be changed. We run a RabbitMQ Cluster on the same hosts as our CouchDB cluster, which means that we need to change the epmd port. We also changed the node name too.

I think with docker that it's possible to bind-mount files as well as directories isn't it? Might be something to suggest as well 👍

[wohali]

Looks like as long as you're not on Windows, you can bind-mount a single file. I'll update.

Any other comments?