Can't access the shell inside of a container.

[ldvy]

Environment

• PostgreSQL version: 11
• PostgREST version: v9.0.0.20220211
• Operating system: Linux

Description of issue

I need to override the default entrypoint of the postgrest container while deploying to K8s. So something like:
<other steps> && postgrest

However, it doesn't work.

I tried to create a dummy container on my computer with the below Dockerfile:

FROM postgrest/postgrest:latest

SHELL ["/bin/bash", "-c"]
CMD echo "test" && postgrest

I've tried using the /bin/sh and /bin/bash pointers, but in both cases, I got an error saying that /bin/*sh wasn't found.

I wonder if there is any shell present in the PostgREST image.
Please let me know if this is the case.

[wolfgangwalther]

No, there is no shell in our docker image. We create a minimal docker image with only the postgrest executable. You can find details about this here: https://github.com/PostgREST/postgrest/blob/main/nix/tools/docker/README.md

For some architectures, we don't provide minimal docker images, yet, so those do have a base system including shell installed. However that's nothing we support, but just a side-effect because we can't built the static executable on those architectures, yet.

I assume you'll need to create a config file or something in those steps before executing postgrest. I suggest you do that in an initContainer running something like busybox or so. You can then mount a volume to that container and put the dynamically created files on that for the postgrest image to consume.

[ldvy]

Thank you @wolfgangwalther , I will do it through the initContainer.
And just a quick follow up question:
Is the configuration file name/location static?
If I put the file elsewhere, how would I go around passing its full location to the postgrest binary upon execution?

[wolfgangwalther]

https://postgrest.org/en/stable/configuration.html#configuration

[ldvy]

@wolfgangwalther ,
As you already mentioned, there is no shell in the image.
In order to pass the configuration file to the postgrest executable, I need to execute the postgrest binary and pass the config file to it as a parameter; so something like:
"postgrest /path/to/file".

The default entrypoint of the image is just a simple execution of the postgrest binary; If I want to specify the config file, I have to override it.
But how can I override it if there is no shell?

Please let me know if there is a different way.

[ldvy]

Either way, thank you for your explanation!

[wolfgangwalther]

You don't need a shell at all to change the command that the image is run with.

I can do:

docker run --rm postgrest/postgrest:v9.0.0 postgrest --help

This will give me the help output. I can replace --help with a path to a configuration file.

For kubernetes, this will be something like:

containers:
- image: postgrest/postgrest:v9.0.0
  command: ['postgrest', 'path/to/config']