When a request arrives for a backend that has been scaled to zero, the interceptor holds the request until the backend becomes ready. You can configure a fallback service and a readiness timeout to control what happens if the backend takes too long to start.

Cold-start fallback

When the readiness timeout expires during a cold start, the interceptor returns an error by default. To serve requests from a fallback service instead, configure the coldStart.fallback field:

apiVersion: http.keda.sh/v1beta1
kind: InterceptorRoute
metadata:
  name: my-app
spec:
  target:
    service: <your-service>
    port: <your-port>
  scalingMetric:
    concurrency:
      targetValue: 100
  coldStart:
    fallback:
      service: <your-fallback-service>
      port: <your-fallback-port>
  timeouts:
    readiness: 5s

When a fallback is configured but the readiness timeout is 0s (disabled), a 30-second default readiness timeout is applied automatically. This prevents the fallback from never being triggered.

Cold-start response header

The interceptor adds an X-KEDA-HTTP-Cold-Start response header to indicate whether a cold start occurred:

• X-KEDA-HTTP-Cold-Start: true — the request triggered a scale-from-zero.
• X-KEDA-HTTP-Cold-Start: false — the backend was already running.

This header is enabled by default. To disable it, see Configure the Interceptor.

What’s Next

• How Scaling Works — cold-start mechanics and scale-from-zero behavior.
• Configure Timeouts — per-route timeout overrides.
• InterceptorRoute Reference — field details for coldStart.