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How is traffic redirected to the ingress from inside the cluster?

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Answer from AI

To redirect traffic from inside the cluster to the Ingress, the DNS name of the Ingress Controller service is used. In the standard configuration, the Ingress Controller is deployed as a Service of type LoadBalancer or NodePort.

  1. Service Discovery: The application inside the cluster uses the DNS name of the Service that exposes the Ingress Controller. For example, nginx-ingress-controller.ingress-nginx.svc.cluster.local, if nginx-ingress is used with the corresponding Service name.

  2. Service IP/ClusterIP: The DNS server of the Kubernetes cluster (e.g., CoreDNS) resolves this DNS name to the ClusterIP Service of the Ingress Controller.

  3. kube-proxy: kube-proxy on the node where the application is running intercepts traffic directed to the ClusterIP Service of the Ingress Controller.

  4. iptables/ipvs: kube-proxy uses iptables or ipvs rules to route traffic to one of the Ingress Controller pods.

  5. Processing in Ingress Controller: The Ingress Controller pods receive the traffic and, according to the Ingress resource rules, redirect it to the appropriate service inside the cluster.

Example request from a pod:

# Request to the service via Ingress, using internal DNS
curl http://my-app.example.com

Here, my-app.example.com is resolved by the cluster's DNS server to the ClusterIP Service of the Ingress Controller if the appropriate records are set or if the Ingress Controller is configured to handle such requests directly (less common for internal traffic). Usually, internal traffic accesses the service by its DNS name. If you need to explicitly go through the Ingress from inside the cluster, ensure that the Ingress Controller is accessible via ClusterIP or the pod's local IP and that DNS or routing mechanisms direct to it.

A more common pattern for service communication inside the cluster is to access the service directly by its DNS name (<service-name>.<namespace>.svc.cluster.local), bypassing the Ingress. Redirecting traffic to the Ingress from inside the cluster is usually needed for testing or specific routing scenarios.

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