Katalyst: 502 Proxy Error (StatusCodeException) when in idle state

Description

• A user working in Katalyst leaves the application idle (“paused work”) and later sees a generic server error in the UI.
• The server logs / error report contains a stack trace similar to:
  com.google.gwt.user.client.rpc.StatusCodeException: 502 Proxy Error
  with HTML content Proxy Error… The proxy server received an invalid response from an upstream server… Error reading from remote server.
• The reported request is often a Katalyst RPC call such as POST /Katalyst/dispatch/RemoteExperimentNames.

Solution

• This error originates from the HTTP proxy or load balancer between the user and the Katalyst application, not from Katalyst logic itself.
• Check proxy/load balancer configuration for:
  • Idle timeout values (connection closed after inactivity).
  • Backend timeout for long‑running or resumed requests.
  • Health checks and routing to the Katalyst application server.
• Adjust timeouts so that:
  • Reasonable periods of user inactivity do not cause the proxy to drop connections in a way that triggers 502 errors on the next request.
  • Backend connections to the Katalyst server are kept alive or cleanly re‑established.
• Monitor proxy and Katalyst logs during reproduction to confirm:
  • Katalyst is running and responds normally when called directly.
  • The 502 is generated by the proxy when it cannot read a response.
• If needed, involve network/infrastructure teams to update proxy policies for the Katalyst URL.