refactor yurthub cache to adapt different storages

[Congrool]

Signed-off-by: Congrool [email protected]

What type of PR is this?

/kind enhancement
/sig storage

What this PR does / why we need it:

Currently, the cacheManager deeply couple with the diskStorage. In #778 , we'll add a new storage backend for cacheManager, called pool-coordiantor which actually an etcd storage at the view of cacheManager. There're some problems need to be solved before implement this feature:

1. the format of key for disk storage is different from that of pool-coordinator, the former is /component/resource/namespace/name and the later is /registry/resource/namespace/name. Also considering that there're some special case for pool-coordinator, such as resource nodes should be minions instead.
2. For update operation, there's also difference. For disk storage, we have to decode the stored json data and retrieve the rv field, but for pool-coordinator we can directly compare the rv in etcd. Also considering that, the comparision and update should be atomic, so we should not compare the rv in cache manager and update in storage.
3. The storage.Store interface is not explict enough. We should define the operation of each function before implementing other storages.
4. We should make the in-memory cache at the level of cachemanager, which is used to optimize the cache query effiency, because there're two many kinds that can read/write storage, it's not easy to manage the in-memory cache. But at the cachemanager layer, only CacheResponse will write to the storage and QueryCache will read from the storage, the management of in-memory cache will be much more easier.

[Congrool]

Currently, it's for preview and has never been tested.

[Congrool]

TODO List:

• revise unit tests
• check the cache ability in actual environment

[Congrool]

Proposal： #897

[codecov]

Codecov Report

Merging #882 (d7b5398) into master (775d69d) will increase coverage by 1.14%.
The diff coverage is 63.90%.

@@            Coverage Diff             @@
##           master     #882      +/-   ##
==========================================
+ Coverage   50.78%   51.92%   +1.14%     
==========================================
  Files          96       98       +2     
  Lines       12795    13371     +576     
==========================================
+ Hits         6498     6943     +445     
- Misses       5754     5846      +92     
- Partials      543      582      +39     

Flag	Coverage Δ
unittests	51.92% <63.90%> (+1.14%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/yurthub/certificate/hubself/fake_cert_mgr.go	0.00% <0.00%> (ø)
pkg/yurthub/filter/servicetopology/filter.go	0.00% <0.00%> (ø)
pkg/yurthub/healthchecker/node_lease.go	91.00% <ø> (ø)
pkg/yurthub/proxy/remote/remote.go	1.35% <0.00%> (ø)
pkg/yurthub/util/util.go	80.15% <ø> (+2.22%)	⬆️
pkg/yurthub/certificate/hubself/cert_mgr.go	20.43% <6.66%> (+0.38%)	⬆️
pkg/yurthub/proxy/local/local.go	70.13% <33.33%> (ø)
pkg/yurthub/proxy/util/util.go	80.07% <45.83%> (-7.55%)	⬇️
pkg/yurthub/healthchecker/health_checker.go	79.86% <52.00%> (-6.09%)	⬇️
pkg/yurthub/kubernetes/meta/restmapper.go	74.07% <55.17%> (-2.40%)	⬇️
... and 13 more

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[Congrool]

I reconsider the timing when merge this pr. It seems more work need to be done than original thought. Is it better to merge this pr after v1.0?

Meanwhile, I'll continue my work about autonomy tests, #778 and #857 based on this pr.

[Congrool]

I've rebased the pr of autonomy e2e tests, and seems that all tests can pass. I think it's ready for review, PTAL @rambohe-ch
And the proposal #897 has been updated, motivations of most modifications are described in it.

[rambohe-ch]

/lgtm
/approve

[openyurt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Congrool, rambohe-ch

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