What causes ‘context deadline exceeded’ errors in an Istio service mesh?

Almost always a mismatch between the Istio VirtualService timeout configuration and the actual upstream service’s response time under load — the default Istio timeout (15s at the route level if unset) can be shorter than a slow downstream call.

Fix

Set explicit, workload-appropriate timeouts on VirtualService routes rather than relying on defaults, and pair with circuit breaking (DestinationRule outlier detection) so a slow dependency doesn’t cascade into mesh-wide latency.