How to use multi-cluster Ingresses - Container Service for Kubernetes

Ingresses function as Layer-7 load balancers for Kubernetes clusters. Configured Ingress rules precisely route external requests to designated backend Services or applications. Through multi-cluster Services and Ingress rules, requests can be distributed across Services deployed in multiple clusters. This topic describes how to work with multi-cluster Ingresses.

Prerequisites

The Fleet management feature is enabled.
The Fleet instance is associated with multiple clusters whose Kubernetes versions are 1.21 or later. For more information, see Associate clusters with a Fleet instance.
The kubeconfig file of the Fleet instance is obtained in the Distributed Cloud Container Platform for Kubernetes (ACK One) console and a kubectl client is connected to the Fleet instance.
The AMC command-line tool is installed.
A multi-cluster Service is created and associated with the backend applications and Services to which the Ingresses route requests. For more information, see MCS overview.
The NGINX Ingress controller is installed in the clusters that are configured with Ingresses and the version of the NGINX Ingress controller is 1.7.0-aliyun.1 or later. For more information, see Update the NGINX Ingress controller.

Usage notes

After configuring multi-cluster Services and Ingress rules, you can route requests to Services deployed across multiple clusters. The following figure shows the workflow:

In this example, Ingresses are created for ACK Cluster 1 and ACK Cluster 2. Applications are deployed in ACK Cluster 1, ACK Cluster 2, and ACK Cluster 3. The following figure shows how multi-cluster Ingresses are used to route requests.

Procedure

Map a multi-cluster Service to the Services in the clusters that are configured with Ingresses.
For more information about how to configure a multi-cluster Service, see Use the CLI to configure MCS.
1. Configure a ServiceExport in each cluster to export the Service in the cluster to the multi-cluster Service.
2. Configure a ServiceImport in each cluster that is configured with an Ingress. The ServiceImport is used to import the multi-cluster Service to the cluster so that the Ingress of the cluster can access the multi-cluster Service. By default, the imported Services are named in the amcs-{Service name} format.
3. Run the following command in the clusters that are configured with Ingresses to query the imported Services:
```
kubectl get service amcs-nginx
NAME         TYPE        CLUSTER-IP        EXTERNAL-IP   PORT(S)   AGE
amcs-nginx   ClusterIP   192.168.118.171   <none>        80/TCP    34m

kubectl get endpointslice
NAME                                                     ADDRESSTYPE   PORTS   ENDPOINTS               AGE
imported-c0c4a2c9339e44235a5228d0b0ff2259c-nginx-vnlnd   IPv4          80      10.0.2.4,10.0.2.5       34m
imported-ce962c460ae284243a3161d6f2c7b4cf7-nginx-d8rr5   IPv4          80      10.0.2.221,10.0.2.236   29m
imported-ca5b667538054499ab399588efe4ab654-nginx-xfe1a   IPv4          80      10.0.2.145,10.0.2.123   20m
```

Configure Ingress rules in the clusters that are configured with Ingresses to expose Services.

Create a file named ingress.yaml and copy the following content to the file:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: multi-cluster-nginx-ingress
spec:
  rules:
  - host: example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: amcs-nginx
            port: 80

Run the following command to configure Ingress rules in the clusters that are configured with Ingresses to route requests to the multi-cluster Service:
```
kubectl apply -f ingress.yaml
```

Query the Ingress endpoints of the clusters that are configured with Ingresses.

# ACK Cluster 1
kubectl get ingress
NAME                          CLASS   HOSTS         ADDRESS         PORTS   AGE
multi-cluster-nginx-ingress   nginx   example.com   XX.XX.XX.XX     80      26m

# ACK Cluster 2
kubectl get ingress
NAME                          CLASS   HOSTS         ADDRESS         PORTS   AGE
multi-cluster-nginx-ingress   nginx   example.com   XX.XX.XX.XX     80      26m

Use DNS resolution to resolve the Ingress domain names.
Create A records to resolve the Ingress domain names to the Ingress addresses of the clusters that are configured with Ingresses. For more information about domain name resolution, see Add DNS records.