Refactor SharedInformers

[manusa]

Description

Shared Informers module was implemented simply by porting the Go-client implementation.

Although everything works fine, there's still room for improvement.

• Create more testable code (clear separation of concerns, and interface segregation)
• Add unit tests to verify implementation
• Check concurrency implementations and thread safety

Relates to:

• Two SharedInformer issues related to kube-apiserver unavailable and relisting #1961
• Revisit SharedInformer support and do Improvements #1894 - Fix #1894: SharedInformer Improvements #1951
• Support a SharedInformer API #1384 - Initial draft for SharedInformer Support #1728
• watch should handle etcd old version exception #1075
• Shared informers should be better supported with adapted clients #2489

[stale]

This issue has been automatically marked as stale because it has not had any activity since 90 days. It will be closed if no further activity occurs within 7 days. Thank you for your contributions!

[shawkins]

After the Informable change I think this can be resolved. The only thing I don't like about the remaining impl is how the resync logic functions - but it matches the go client so it's probably not worth tweaking further.

[shawkins]

Marking as resolved based upon the last comment.

[manusa]

@shawkins Thank you very much for your tremendous effort making this happen.

I'm sure that our Shared Informer implementation and all the extra-features around it are some of the main differentiating traits that make the Fabric8 client special and maybe better as compared to its competition.

🙌