Support hot reloading for mounted volume configmaps and secrets about micronaut-kubernetes HOT 9 OPEN

Hi @StephanePaulus, first of all huge thank you for taking this initiative and POC!

library supports reading configmaps from mounted volumes.

Yeah, this is definitely smth we do not support yet, I'll fix the guideline, thanks for this and sorry for misleading you.

I would like to ask for advice and if there is a need for this besides my own. In my case I am not allowed to use the kubernetes API, so mounted volumes is the only way I can read configmaps or secrets.

That's good point and use case. Feel free to create PR and I can take it over if you like or I can provide you initial code review and you can finish the work yourselves.

Thanks again.

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Hi @pgressa, please let me know if you feel like the PR is not what you were expecting. Maybe we can come up with a better solution. If you are waiting for me to fully complete the PR, with all test passing please let me know.

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Hi @StephanePaulus, first of sorry for being quite for some time. Once again thanks for the PR. I'd like to get beck to this feature now.

To answer question #315:
For the secrets case I think we could either add the file path of the variables, so for the secret :

apiVersion: v1
kind: Secret
metadata:
  name: mysecret
type: Opaque
data:
  username: YWRtaW4=
  password: MWYyZDFlMmU2N2Rm

and configuration

kubernetes:
  client:
    enabled: false
    watch: true
    secrets:
      enabled: true
      paths:
        - /etc/example-service/secrets

So the property source name would be then:

• file path etc.example-servce.secrets.username resp etc.example-servce.secrets.password

Another option is to extend the configuration with the defined prefix:

kubernetes:
  client:
    enabled: false
    watch: true
    secrets:
      enabled: true
      items:
        - path: /etc/example-service/secrets
           namePrefix: foo.bar 

What do you think?

Where to place it
Ideally this feature can find its way into https://github.com/micronaut-projects/micronaut-discovery-client in the future but at this moment let's keep it focused entirely on K8s use case.

I'll take over the PR and continue on it if you're not against it.

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@pgressa yes sure you can take over. I could share the new code I have in a private repository, that already fixes some bad file watching stuff. Let me know if I can be of any assistance.

I think the namePrefix option is the cleanest.

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I was thinking about deduplicating the code by providing more generic approach like:

kubernetes:
  client:
    external:
      - name: <optional-name-of-the-property>, defaults to the "basename <path>"
         path: <mandatory-path-to-file>
         type: <mandatory-file-type> [file-per-property|structered-configuration], no default
         watch: [true/false]
         enabled: [true/false]

• This approach brings certain level of extensibility by providing the type file resolver.

also @StephanePaulus if you could share the new code I would be glad for it. Thanks.

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@pgressa here you can find the updated code that worked good enough for me. It is not perfect, but it did the job. code repo

Your approach looks very generic and will solve all issues I am trying to fix.

How kubernetes adds mounted files to the filesystem of a container is kind of tricky. When using the normal filewatcher you need to do special logic, because the files are just symbolic links. And the main folder is "..data"

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@pgressa Sorry to ask you, but do you have an idea when this feature/fix can be available?

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@StephanePaulus sorry for the delay, I have extracted the loading of config maps mounted as volumes into this PR #365. The hot reloading will be subject of some other PR in the future.

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@StephanePaulus I have removed the part "Add support to load configmaps when mounted as a volume. " from the title, since that's is already merged.

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