[v12] Prevent races creating web api session context #23733
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Closes #23533 and #20963. There was a race to create the `web.SessionContext` for a session when multiple Proxies are behind a load balancer. Only the Proxy that processes the login will have a `web.SessionContext` created for the session. Any subsequent requests to the other Proxies in the pool would create one if the request was authenticated. However, multiple requests within a short succession could cause a single Proxy to create multiple `web.SessionContext` for a single session. When that happens the most recently created `web.SessionContext` gets saved and the previous `web.SessonContext` gets closed. Closing causes the `auth.Client` to be closed, which causes any active requests for that client to return with a `grpc: client connection is closing` error. This manifests in a single request from the web UI to fail and depending on the request, for a banner to be displayed with the error. Refreshing the page or navigating to another page would resolve the problem because the most recent `web.SessionContext` would be used with the still open `auth.Client`. To prevent `web.Handler.AuthenticateRequest` from racing to create the `web.SessionContext` a `singleflight.Group` was added to the `web.sessionCache`. When multiple requests come in for the same session they now will all use the first `web.SessionContext` to be created instead of each creating their own.
zmb3
approved these changes
Mar 28, 2023
espadolini
approved these changes
Mar 28, 2023
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Backport #23691 to branch/v12