Use LinearCache to optimize StreamEndpoint discovery.

[tsaarni]

This change attempts to improve performance in clusters with a large number of endpoints, as discussed in #6743 (comment). The PR replaces use of Envoy go-control-plane SnapshotCache with LinearCache for EDS.

The LinearCache was previously considered but not adopted due to complications outlined by @skriss in a prior PR

If Envoy already has config for a given resource at a particular version, then on a control plane restart, the version number of the resource in the cache will be reset to 1 (or close to 1), therefore will not be sent to Envoy since Envoy already has a "later" version of the resource.

This PR attempts to mitigate this by generating unique version prefix at each startup.

Fixes #6743

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 5 lines in your changes missing coverage. Please review.

Project coverage is 80.79%. Comparing base (38346c5) to head (7bc7a34).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/xdscache/v3/endpointslicetranslator.go	0.00%	3 Missing ⚠️
internal/xdscache/v3/snapshot.go	93.10%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6906      +/-   ##
==========================================
+ Coverage   80.70%   80.79%   +0.08%     
==========================================
  Files         131      131              
  Lines       19816    19802      -14     
==========================================
+ Hits        15993    15999       +6     
+ Misses       3533     3514      -19     
+ Partials      290      289       -1     

Files with missing lines	Coverage Δ
internal/xdscache/v3/endpointstranslator.go	86.66% <100.00%> (-0.79%)	⬇️
internal/xdscache/v3/snapshot.go	86.53% <93.10%> (+8.12%)	⬆️
internal/xdscache/v3/endpointslicetranslator.go	79.09% <0.00%> (+4.58%)	⬆️

[davinci26]

before I review, we are extremely interested in this but is there a way to have this behind a feature flag?

Coming from a bit of ignorance but could contour be updated in place and things should just work or would it require to restart all the envoy pods?

[tsaarni]

before I review, we are extremely interested in this but is there a way to have this behind a feature flag?

I have not worked with go-control-plane and xDS subscription versioning details, so this should be carefully reviewed. I'd appreciate extra eyes on this.

If necessary, we can add a feature flag, but I'm not sure if it is needed - see below.

Coming from a bit of ignorance but could contour be updated in place and things should just work or would it require to restart all the envoy pods?

I don't believe Envoy pods need to be restarted. As far as I understand, Envoys are completely unaware of the algorithm the server uses; they simply return the last received version info to the server.

I'm still working on fully understanding the difference between the cache implementations. I created https://github.com/tsaarni/grpc-json-sniffer to gain more insight into this issue.

[tsaarni]

I've ran some test scenarios and documented them here https://gist.github.com/tsaarni/db319d5d9935d18f8856fcdd9b2a89ae

The go-control-plane cache implementations have some details that might be interesting to study as well

• SnapshotCache https://github.com/envoyproxy/go-control-plane/blob/main/pkg/cache/v3/simple.go https://github.com/envoyproxy/go-control-plane/blob/main/pkg/cache/v3/snapshot.go
• LinearCache https://github.com/envoyproxy/go-control-plane/blob/main/pkg/cache/v3/linear.go