Istio 503 NR (No Route Configured)

What is Istio 503 NR (No Route Configured)

Symptom

503 NR (No Route Configured)

Root Cause

No route is configured for the requested service.

Understanding Istio and Its Purpose

Istio is an open-source service mesh that provides a way to control how microservices share data with one another. It provides a range of features such as traffic management, security, and observability, making it easier to manage complex microservice architectures. For more information, you can visit the official Istio documentation.

Identifying the Symptom: 503 NR (No Route Configured)

When working with Istio, you might encounter the error code 503 NR, which stands for 'No Route Configured'. This error typically manifests as a service being unreachable, resulting in a 503 Service Unavailable response.

Explaining the Issue: No Route Configured

The 503 NR error indicates that there is no route configured for the requested service. This usually happens when the Istio proxy (Envoy) does not have the necessary routing information to forward the request to the intended service. This can occur due to missing or misconfigured VirtualService resources.

Common Causes

VirtualService is not defined for the service. Incorrect host or destination in the VirtualService. VirtualService is not applied to the correct namespace.

Steps to Fix the 503 NR Issue

To resolve the 503 NR error, follow these steps:

Step 1: Verify VirtualService Configuration

Check if a VirtualService is defined for the service. You can list all VirtualServices in a namespace using:

kubectl get virtualservices -n <namespace>

If the VirtualService is missing, create one with the correct routing rules.

Step 2: Check Host and Destination

Ensure that the host and destination specified in the VirtualService match the service name and namespace. Here is an example of a correct VirtualService configuration:

apiVersion: networking.istio.io/v1alpha3kind: VirtualServicemetadata: name: my-servicespec: hosts: - my-service http: - route: - destination: host: my-service port: number: 80

Step 3: Apply VirtualService to the Correct Namespace

Ensure that the VirtualService is applied to the same namespace as the service. If not, reapply it using:

kubectl apply -f my-virtualservice.yaml -n <namespace>

Conclusion

By ensuring that your VirtualService is correctly configured and applied, you can resolve the 503 NR error and ensure that your services are reachable. For further troubleshooting, refer to the Istio network issues guide.

Tool

istio