Verify zone-aware routing on an ASM instance topology - Alibaba Cloud Service Mesh

In multi-zone deployments, cross-zone traffic adds latency and data transfer costs. Zone-aware routing directs traffic to service endpoints in the same zone as the caller. When a same-zone endpoint becomes unavailable, traffic automatically fails over to endpoints in other zones.

This tutorial uses the Bookinfo sample application to demonstrate both behaviors on the ASM topology:

Same-zone preference: Traffic from productpage routes to reviews-v1 in the same zone.
Cross-zone failover: When reviews-v1 becomes unavailable, traffic shifts to reviews-v2 in a different zone.

Prerequisites

Before you begin, make sure that you have:

An ASM instance. See Create an ASM instance
An ACK managed cluster added to the ASM instance. See Create an ACK managed cluster and Add a cluster to an ASM instance
Cluster nodes distributed across at least two zones. This tutorial uses cn-hangzhou-j and cn-hangzhou-k. To check zone assignments, see the node details in the ACK console. For more information, see Regions and zones
An ingress gateway deployed with topology viewing enabled. See Get started
Helm 3 installed on your local machine

Step 1: Deploy the sample application

Download the Helm chart for the sample application.
Extract the package and open the asm-az-routing directory. In values.yaml, set the zones where the application deploys:
```
zone1: cn-hangzhou-j
zone2: cn-hangzhou-k
```
This deploys reviews-v1 in cn-hangzhou-j and reviews-v2 in cn-hangzhou-k.

Install the chart:

helm install --namespace azdemo azdemo ./

After all pods are running, send continuous requests through the ingress gateway:
```
while true; do
  curl -I http://<ingress-gateway-ip>/productpage
  echo; sleep 1
done
```
Replace <ingress-gateway-ip> with the IP address of your ingress gateway. Press Ctrl+C to stop.

Step 2: Confirm same-zone routing on the topology

Log on to the ASM console. In the left-side navigation pane, choose Service Mesh > Mesh Management.
Click the name of the ASM instance. In the left-side navigation pane, choose Observability Management Center > Mesh Topology.
Click Copy token and open in new window.
On the logon page, enter the token and click log in.
Select the namespace of the ASM instance. From the Display drop-down list, select Traffic Distribution, Traffic Rate, and Traffic Animation. Deselect Service Nodes.

The topology shows traffic flowing from productpage-v1 to reviews-v1 in the same zone, confirming that zone-aware routing is active.

Step 3: Verify cross-zone failover

Simulate a zone failure by scaling reviews-v1 to zero pods, then observe the traffic shift.

In the ACK console, navigate to Clusters and click the cluster name. Choose Workloads > Deployments.
Find the reviews-v1 deployment, click Scale in the Actions column, set Desired Number of Pods to 0, and click OK.
Return to the Mesh Topology page opened in Step 2.

The topology now shows productpage-v1 routing to reviews-v2. This confirms cross-zone failover: when the same-zone reviews service is unavailable, traffic automatically routes to the reviews service in another zone.

Step 4: Verify routing recovery

Restore reviews-v1 and confirm that traffic returns to the same-zone endpoint.

In the ACK console, navigate to Workloads > Deployments for the same cluster.
Find the reviews-v1 deployment, click Scale in the Actions column, set Desired Number of Pods to 1, and click OK.
Return to the Mesh Topology page opened in Step 2.

The topology shows productpage-v1 routing back to reviews-v1 in the same zone, confirming that zone-aware routing recovers after the endpoint is restored.