Prevent LoadBalancer updates on follower. #6872

tsaarni · 2025-01-20T18:20:02Z

This PR fixes a memory leak that was triggered by LoadBalancer status updates. Only the leader instance runs loadBalancerStatusWriter and therefore follower does not have anyone reading from the channel that receives status updates. The LoadBalancer status updates are still watched by followers and sent to the channel, causing the go routine calling ServiceStatusLoadBalancerWatcher.notify() to block. This led to LoadBalancerStatus updates piling up and consuming memory, eventually causing an out-of-memory condition and killing the Contour process.

With this change, Service updates are watched only after the instance becomes the leader and starts the loadBalancerStatusWriter.

Fixes #6860

codecov · 2025-01-20T18:28:46Z

Codecov Report

Attention: Patch coverage is 0% with 30 lines in your changes missing coverage. Please review.

Project coverage is 80.73%. Comparing base (7e2dcaf) to head (0ea6f5c).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/contour/ingressstatus.go	0.00%	27 Missing ⚠️
cmd/contour/serve.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6872      +/-   ##
==========================================
- Coverage   80.77%   80.73%   -0.05%     
==========================================
  Files         131      131              
  Lines       19936    19946      +10     
==========================================
  Hits        16104    16104              
- Misses       3540     3550      +10     
  Partials      292      292

Files with missing lines	Coverage Δ
cmd/contour/serve.go	`22.30% <0.00%> (+0.41%)`	⬆️
cmd/contour/ingressstatus.go	`24.59% <0.00%> (-6.99%)`	⬇️

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Levi080513 · 2025-01-21T02:12:06Z

internal/k8s/statusaddress.go

 func (s *ServiceStatusLoadBalancerWatcher) notify(lbstatus core_v1.LoadBalancerStatus) {
-	s.LBStatus <- lbstatus
+	if s.leader.Load() {


Is it possible to lose the envoy service event in this way?

True. Currently the event processing logic relies on Added/Updated/Deleted events alone. It works for other resource types as they will be processed by all Contour instances but I think new approach is needed with the load balancer status updates.

Maybe we can simply handle it. Notify the latest envoy service when it becomes Leader.

I've changed the approach to start the service watcher only after the instance becomes the leader.

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github-actions · 2025-04-12T00:27:45Z

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Start watching Service updates only after becoming leader, when starting loadBalancerStatusWriter. This avoids piling up unprocessed Service updates on follower instance, consuming memory and eventually causing an out-of-memory condition and killing Contour process. Signed-off-by: Tero Saarni <tero.saarni@est.tech>

tsaarni · 2025-05-05T07:42:37Z

Some notes for manual testing:

Prepare environment with modified Contour

kubectl apply -f https://projectcontour.io/quickstart/contour.yaml
make container 
docker tag ghcr.io/projectcontour/contour:$(git rev-parse --short HEAD) localhost/contour:latest
kind load docker-image localhost/contour:latest --name contour
kubectl -n projectcontour set image deployment/contour contour=localhost/contour:latest

Then create HTTPProxy

kubectl apply -f https://raw.githubusercontent.com/tsaarni/devenvs/refs/heads/main/contour/manifests/echoserver.yaml

Set IP address for service

kubectl -n projectcontour patch service envoy --type=merge --subresource=status --patch '"status": {"loadBalancer":{"ingress":[{"ip":"1.2.3.4"}]}}'

Check that the address is reflected on HTTPProxy

kubectl get httpproxy echoserver -o jsonpath='{.status.loadBalancer.ingress[*].ip}'

Scale down replicas to zero and change address while Contour is down

kubectl -n projectcontour scale deployment --replicas=0 contour
kubectl -n projectcontour patch service envoy --type=merge --subresource=status --patch '"status": {"loadBalancer":{"ingress":[{"ip":"1.2.3.5"}]}}'

Scale up and check that leader picks up the latest address and updates the HTTPProxy

kubectl get httpproxy echoserver -o jsonpath='{.status.loadBalancer.ingress[*].ip}'

sunjayBhatia

Nice fix! yeah the load balancer status writer already has other informers for updating resources that need the load balancer status and it makes sense to start the load balancer service watcher there too, since it only needs to run on the leader instance

tsaarni requested a review from a team as a code owner January 20, 2025 18:20

tsaarni requested review from skriss and sunjayBhatia and removed request for a team January 20, 2025 18:20

sunjayBhatia requested review from a team, davinci26 and izturn and removed request for a team January 20, 2025 18:20

tsaarni force-pushed the lbstatus-on-follower branch from 8b2af7d to 920d0ce Compare January 20, 2025 18:22

tsaarni added the release-note/small A small change that needs one line of explanation in the release notes. label Jan 20, 2025

Levi080513 reviewed Jan 21, 2025

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tsaarni marked this pull request as draft January 21, 2025 18:21

github-actions bot added the lifecycle/stale Denotes an issue or PR has remained open with no activity and has become stale. label Feb 10, 2025

github-actions bot closed this Mar 13, 2025

tsaarni removed the lifecycle/stale Denotes an issue or PR has remained open with no activity and has become stale. label Mar 13, 2025

tsaarni reopened this Mar 13, 2025

github-actions bot added lifecycle/stale Denotes an issue or PR has remained open with no activity and has become stale. and removed lifecycle/stale Denotes an issue or PR has remained open with no activity and has become stale. labels Mar 28, 2025

github-actions bot added the lifecycle/stale Denotes an issue or PR has remained open with no activity and has become stale. label Apr 12, 2025

tsaarni force-pushed the lbstatus-on-follower branch 3 times, most recently from fc9581e to a2a792e Compare May 3, 2025 10:32

github-actions bot removed the lifecycle/stale Denotes an issue or PR has remained open with no activity and has become stale. label May 4, 2025

tsaarni force-pushed the lbstatus-on-follower branch from a2a792e to 0ea6f5c Compare May 5, 2025 07:36

tsaarni marked this pull request as ready for review May 5, 2025 07:42

sunjayBhatia requested a review from a team May 5, 2025 07:42

sunjayBhatia approved these changes May 5, 2025

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sunjayBhatia merged commit 154999b into projectcontour:main May 5, 2025
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Prevent LoadBalancer updates on follower. #6872

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