helm-chart: prevent Traefik from ignoring the backend ingress rule #7859
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WalkthroughThe update enhances the Helm chart by introducing a fix to prevent premature 200 OK responses from API endpoints before backend readiness. It increments the chart version from Changes
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There is a condition that may occur during Kubernetes deployment, where the frontend service already has an endpoint (i.e. the frontend pod), but the backend service does not. For example, the backend pod may not have started yet or the service controller may not have had time to react to the backend pod. In this case, when Traefik serves a request with an `/api/...` path, it will see that it matches the `/api` rule, but since the corresponding service has no endpoints, it will _skip_ that rule and try other rules. And since the `/` rule matches everything, it will then route the request to the frontend. This is confusing and unhelpful, and more importantly, it makes health checks return the wrong result. Since the frontend will serve `index.html` to every request, a request to `/api/server/health/` or `/api/server/about` will return a 200 code, even though the server isn't actually up. Because of this bug, I have observed weird failures in the Helm workflow, where the "Wait for CVAT to be ready" step completes, but CVAT is not actually ready. (FYI: The failures I've seen are actually in a private repo, but the failure condition could occur in this repo too. It's just more likely in a private repo, because GitHub uses smaller runners in private repos.) The fix is simple: use the `allowEmptyServices` Traefik setting, which disables the rule skipping behavior. With this setting on, Traefik will return a 503 response for backend URLs until the backend service gains an endpoint.
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Files selected for processing (3)
- changelog.d/20240507_140615_roman_allow_empty_services.md (1 hunks)
- helm-chart/Chart.yaml (1 hunks)
- helm-chart/values.yaml (1 hunks)
Files skipped from review due to trivial changes (3)
- changelog.d/20240507_140615_roman_allow_empty_services.md
- helm-chart/Chart.yaml
- helm-chart/values.yaml
azhavoro
approved these changes
May 13, 2024
Merged
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Motivation and context
There is a condition that may occur during Kubernetes deployment, where the frontend service already has an endpoint (i.e. the frontend pod), but the backend service does not. For example, the backend pod may not have started yet or the service controller may not have had time to react to the backend pod.
In this case, when Traefik serves a request with an
/api/...path, it will see that it matches the/apirule, but since the corresponding service has no endpoints, it will skip that rule and try other rules. And since the/rule matches everything, it will then route the request to the frontend.This is confusing and unhelpful, and more importantly, it makes health checks return the wrong result. Since the frontend will serve
index.htmlto every request, a request to/api/server/health/or/api/server/aboutwill return a 200 code, even though the server isn't actually up.Because of this bug, I have observed weird failures in the Helm workflow, where the "Wait for CVAT to be ready" step completes, but CVAT is not actually ready. (FYI: The failures I've seen are actually in a private repo, but the failure condition could occur in this repo too. It's just more likely in a private repo, because GitHub uses smaller runners in private repos.)
The fix is simple: use the
allowEmptyServicesTraefik setting, which disables the rule skipping behavior. With this setting on, Traefik will return a 503 response for backend URLs until the backend service gains an endpoint.How has this been tested?
I deployed the Helm chart, then ran a
kubectl delete deployments.apps cvat-backend-serverto simulate the server being unavailable. Then I curled the/api/server/health/endpoint.Checklist
developbranch[ ] I have updated the documentation accordingly[ ] I have added tests to cover my changes[ ] I have linked related issues (see GitHub docs)[ ] I have increased versions of npm packages if it is necessary(cvat-canvas,
cvat-core,
cvat-data and
cvat-ui)
License
Feel free to contact the maintainers if that's a concern.
Summary by CodeRabbit
Bug Fixes
New Features
Documentation
0.12.0to0.12.1.