Extending DB initialization in docker-entrypoint.sh

[md5]

I'm working on creating a PostGIS container based on this one and ended up replacing the docker-entrypoint.sh with my own modified version in order to create a template_postgis database (cf. https://github.com/md5/docker-postgis/blob/master/docker-entrypoint.sh#L10-17).

I'd like to propose that docker-entrypoint.sh somehow be extended to allow derived images to do additional work when a new database is being initialized. I can provide a PR with a patch, assuming there's agreement that this is a desirable change. I'd probably default to using a /docker-entrypoint.d/ directory or something of that sort.

[md5]

It looks like this issue was also alluded to in #16.

[tianon]

I'm definitely +1 on something like /docker-entrypoint-initdb.d (specific to initdb, since that's the situation these would be run in), especially if it makes it easier to use the script as-is and not have to copy it over and sync any future updates yourself.

So in that case, maybe it should even run at the end of that if block, so that our postgresql.conf and pg_hba.conf could be reverted or changed by these scripts as well. What do you think?

[md5]

I'm fine with running it after the *.conf changes. I'll submit a PR for this soon and use the name docker-entrypoint-initdb.d. I'll also create a PR for docker-library/docs to document the feature.