Backend manager re-design

[mihivagyok]

• This PR refactors how the backends are added to backend manager, but it is working same as before
• Instead of multiple backendManagers, use one backendManger
• The one backendManager could be configured with different proxy strategies
  e.g.
  • earlier:

   backendManager1 - destHost
   backendManager2 - default
  

  • now:

  backendManager - destHost,default
  

• Earlier, based on agentIdentier and backendManagers, the addBackend->Addbackend->newBackend functions were called with the very same agent backend connection
• Within one backend definition, the connection is guarded by a mutex

type backend struct {
	// TODO: this is a multi-writer single-reader pattern, it's tricky to
	// write it using channel. Let's worry about performance later.
	mu   sync.Mutex // mu protects conn
	conn agent.AgentService_ConnectServer
}

• As the current code creates multiple backends with the same connection, this is ineffective

• that's why let's change the backendManager logic

  • have one BackendManager
  • call the newBackend function only one per backend
  • populate the same backend instance for the configured proxy strategies

• Why do we need this? This solves many issues based on our testing like

• konnectivity fails on kubectl cp #261 - I think if there are multiple strategies and multiple client calls to the server, it could happen that the server call the send() on a connection which is already in the 'sending' state. After that the backend just hangs in the server - other backends with the same connection could still work. That's why there is also memory leak probably in the server side (Konnectivity server leaks memory and free sockets #255)

• fixes this as now the addBackend always return one backend (Server running with --proxy-strategies=destHost panics even if agent has correct --agent-identifiers #316) - although I don't understand what panics mean in the issue

• I have tested my scenarios and it works quite okay, so I really think this change is needed and crucial for konnectivity stability

• I have only reworked the AddBackend function, the RemoveBackend function is the same - but that does not matter.

• I have also created unit tests for proxy strategy testing

[k8s-ci-robot]

Hi @mihivagyok. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[andrewsykim]

/assign @andrewsykim @cheftako

[andrewsykim]

/ok-to-test

[mihivagyok]

/retest

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/lifecycle stale

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/lifecycle rotten

[k8s-ci-robot]

@mihivagyok: PR needs rebase.

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/close

[k8s-ci-robot]

@k8s-triage-robot: Closed this PR.

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/close

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[mihivagyok]

/remove-lifecycle stale

[mihivagyok]

/reopen

[k8s-ci-robot]

@mihivagyok: Reopened this PR.

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/reopen

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mihivagyok
Once this PR has been reviewed and has the lgtm label, please ask for approval from andrewsykim by writing /assign @andrewsykim in a comment. For more information see:The Kubernetes Code Review Process.

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/close

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@k8s-triage-robot: Closed this PR.

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/close

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[cheftako]

/reopen
/remove-lifecycle rotten

[k8s-ci-robot]

@cheftako: Reopened this PR.

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/reopen
/remove-lifecycle rotten

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[k8s-ci-robot]

@mihivagyok: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-apiserver-network-proxy-make-lint	af6f594	link	true	/test pull-apiserver-network-proxy-make-lint
pull-apiserver-network-proxy-docker-build-amd64	af6f594	link	true	/test pull-apiserver-network-proxy-docker-build-amd64
pull-apiserver-network-proxy-docker-build-arm64	af6f594	link	true	/test pull-apiserver-network-proxy-docker-build-arm64
pull-apiserver-network-proxy-test	af6f594	link	true	/test pull-apiserver-network-proxy-test

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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/lifecycle stale

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/lifecycle rotten

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/close

[k8s-ci-robot]

@k8s-triage-robot: Closed this PR.

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