Create /docker-entrypoint-initdb.d directory by default

[mmarzantowicz]

Currently one needs to put at last two lines to install custom initialization script:

RUN mkdir /docker-entrypoint-initdb.d
COPY ./some-script.sh /docker-entrypoint-initdb.d/some-script.sh

There would be no harm to have empty /docker-entrypoint-initdb.d directory for user scripts but it would make extending images easier by reducing previous example to:

COPY ./some-script.sh /docker-entrypoint-initdb.d/some-script.sh

As a side effect, this change would also simplify docker-entrypoint.sh (one test less) but what is most important here, users will gain ability to just COPY their scripts without need to manage destination directory (which is already specified in docker-entrypoint.sh.)

[yosifkit]

Oh, good point. Do you want to make a PR for it? The easy way to do it for this repo is to update Dockerfile.template and then run update.sh. If you want to just update the template I can run the update afterward.

[mmarzantowicz]

Is it OK to put it just after line 33 or should it go before 39?

[tianon]

I'd actually prefer it be added just above line 18 there so that we get maximum cache-potential out of it (especially since it'll be an empty layer).

[mmarzantowicz]

Apologize, I was to quick in my "improvement" proposition. I've just read docker docs and there is written about COPY instruction that :

If doesn't exist, it is created along with all missing directories in its path.

Doing simple COPY (or ADD) of initialization script in derived image should be sufficient to create /docker-entrypoint-initdb.d directory.

Maybe we can provide some example in docs so users have no doubts how to play nicely with custom scripts.

[tianon]

I think having the explicit "mkdir" would still be useful, since then we
can easily do things like "RUN echo 'some-stuff-here'

/docker-entrypoint-initdb.d/myscript.sh" without having to mkdir
ourselves first. It's also less surprising for users if we say "put your
scripts in XYZ directory" and XYZ actually exists. :)