st2actionrunner: Missing entrypoint.d

[fjudith]

Describe the problem
Preview version of st2docker enabled entrypoint customization allowing a to add additionnal binairies and configuration files, without requiring to build a devired image

This feature has diseapered with the 3.3.0 release and is not documented in the release note.

What is the recommended approach for people that want to customize the st2actionrunner ?

Versions

• Host OS: [e.g. Ubuntu 18.04] 18.04
• docker: [e.g. 18.09.1-ce] 18.09.1-ce
• docker-compose: [e.g. 1.21.1] 1.21.1
• stackstorm version: [e.g. v3.3.0] v3.3.0

To Reproduce
If necessary, please specify steps to reproduce the behavior.

Running any Packs that require additionnal binaries (Terraform, Salt, Ansible, etc)

[arm4b]

I guess in terms of Docker image immutability it's an anti-pattern to include some kind of time-consuming operation (like package installation, etc) during the container startup as it affects the time ST2 cluster becomes ready and there is no guarantee that command will succeed which may bring you a failed cluster and reproducibility issue. From the production standpoint it's indeed better to build your own st2actionrunner images.

From the other side I understand the reason that it's not always makes sense to build the new images from scratch in some environments and K8s has initContainers for this to do some minimal pre-configuration changes before the startup.

As a workaround you could overwrite the CMD aka entrypoint (https://docs.docker.com/compose/compose-file/#entrypoint) inside the docker-compose.yaml for the st2 services where you need specific changes before starting the st2 on them.
We'd also welcome to see the design ideas for integrating and contributing this kind of functionality into st2-docker 👍