Switch to new compose library

[k9withabone]

I'm currently developing a new Rust library which does a better job of conforming to the compose-spec. The library can be found at k9withabone/compose_spec_rs. For podlet, it will replace the docker-compose-types library currently used.

The new library will be completely documented, conform only to the compose-spec, fully parse and validate each part of compose files, and adhere to semantic versioning. That last part is especially important as I plan to turn all the conversion logic of podlet into a library so that it can be used to create a web version of podlet.

This issue is blocked until the compose_spec library is ready and published.

[k9withabone]

An initial version of the library should be ready to be published once k9withabone/compose_spec_rs#1 is completed. Podlet can then switch to it as the other features (merging, interpolation, etc.) are not a requirement.

[k9withabone]

compose_spec v0.1.0 has been published! Time to start working on the migration.

[k9withabone]

I'm a bit stuck on figuring out how a service Dependency (from the depends_on long syntax) should be converted to a systemd unit dependency. My thinking is currently this:

• Only support the service_started condition, suggesting to use, in the dependency's definition, Notify=healthy under [Container] for service_healthy and Type=oneshort under [Service] for service_completed_successfully.
• If restart is true require that required is also true and add the service to PartOf=. Otherwise, add the service to Requires= or Wants= depending on required.
• Add the service to After=.

Is it correct to use PartOf= for restart or should something like ReloadPropagatedFrom= along with Requires= or Wants= be used instead? Also, maybe StopPropagatedFrom= should always be used for a dependency?

I'm not sure who the best person to ask about this is, but @cdrage, since you worked on kompose, what do you think about this?

[cdrage]

I'm a bit stuck on figuring out how a service Dependency (from the depends_on long syntax) should be converted to a systemd unit dependency. My thinking is currently this:

• Only support the service_started condition, suggesting to use, in the dependency's definition, Notify=healthy under [Container] for service_healthy and Type=oneshort under [Service] for service_completed_successfully.
• If restart is true require that required is also true and add the service to PartOf=. Otherwise, add the service to Requires= or Wants= depending on required.
• Add the service to After=.

Is it correct to use PartOf= for restart or should something like ReloadPropagatedFrom= along with Requires= or Wants= be used instead? Also, maybe StopPropagatedFrom= should always be used for a dependency?

I'm not sure who the best person to ask about this is, but @cdrage, since you worked on kompose, what do you think about this?

To be honest, we never found an answer and did not incorporate it with Kompose :( See: https://kompose.io/conversion/

There's no equivalent for it within Kubernetes.

We instead just have to explain to others that your application should be built-in with retry methods / retrying if it cannot connect to something / timeout instead of having to implement depends_on in a hacky way.

[k9withabone]

Since I haven't been able to find help for this I'm going to go with what I outlined above (using PartOf=) for now. It can always be changed later if someone has a better idea.

[k9withabone]

Actually, looking at the systemd.unit docs again, it seems I actually want BindsTo= instead of PartOf=.