A system is serving high availability. In this context, from the viewpoint of a gateway, when should a request be re-routed?

Question

BlackTom AI · Accepted Answer

In this question about high-availability behavior from a gateway perspective, we must evaluate each scenario to determine when rerouting makes sense.
Option a: 'When a cache replica or partition is not available' — The unavailability of a cache replica or partition is typically a cache-layer concern. While it might cause a slower response or a cache miss, it does not automatically imply that the gateway should reroute to a different service instance, especially if the underlying service is still healthy and capable of serving requests. Rerouting is usually reserved for failures or degraded health in the service path, not purely cache-layer outages. Therefore, this is not consistently a trigger for re-routing.
Option b: 'When a request to a service fails' — This aligns with a core HA principle: if the target service cannot fulfill the request due to failure, the gateway should reroute to another healthy instance or failover target to maintain availability. This is a direct reason to re-route because the current route cannot satisfy the user’s request.
Option c: 'When an HTTP 204 - No Content was received' — HTTP 204 indicates a successful request with no payload. It is not an error condition and does not imply that the gateway should re-route. Rerouting would not be warranted on receiving a 204 in normal operation, since the response is valid.
Option d: 'When an HTTP 408 - Request Timeout was received' — A 408 indicates the client’s request timed out before the server could respond. This is typically treated as a failure to complete the request in time, which justifies attempting an alternate path or replica to fulfill the request, so rerouting is appropriate in this scenario.
In summary, rerouting is generally triggered by actual failures or timeouts in serving the request (options b and d), while cache-only issues or a normal 204 response do not inherently require rerouting. It's important to distinguish between transient cache behavior and end-to-end service health when deciding to re-route.

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A system is serving high availability. In this context, from the viewpoint of a gateway, when should a request be re-routed?

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