Configuring URL Rewriting for a LoadBalancer Ingress

Dedicated LoadBalancer ingresses allow you to rewrite the URLs that match a regular expression. To rewrite the URL for such an ingress, do as follows:

Configure a path that matches a regular expression for the ingress, for example, /first/(.*)/(.*)/end.
Configure a rewrite annotation to match the regular expression in the path.

For example:

Set path to /first/(.*)/(.*)/end and annotation to /$1/$2. When the request sent by the user is /first/aaa/bbb/end, the path matches /first/(.*)/(.*)/end. The rewriting rule replaces $1 with aaa and $2 with bbb, the request path received by the backend server is /aaa/bbb.
Set path to /first/(.*)/end and annotation to /newpath/$1. When the request sent by the user is /first/aaa/end, the path matches /first/(.*)/end. The rewriting rule replaces $1 with aaa, the request path received by the backend server is /newpath/aaa.

This function relies on the ELB capability and is being introduced to all regions. Before using this function, verify if it is available by checking the console options in the current region.

Prerequisites

A CCE standard cluster is available, and the cluster version meets the following requirements:
- v1.23: v1.23.14-r0 or later
- v1.25: v1.25.9-r0 or later
- v1.27: v1.27.6-r0 or later
- v1.28: v1.28.4-r0 or later
- Other clusters of later versions
An available workload has been deployed in the cluster for external access. If no workload is available, deploy a workload by referring to Creating a Deployment, Creating a StatefulSet, or Creating a DaemonSet.
A Service for external access has been configured for the workload. Services Supported by LoadBalancer Ingresses lists the Service types supported by LoadBalancer ingresses.

Notes and Constraints

This feature is only available when dedicated load balancers are used.

Configuring URL Rewriting for a LoadBalancer Ingress

You can configure a URL rewriting rule for an ingress using either the CCE console or kubectl.

Using kubectl

URL rewriting rules of an ingress can be configured using annotations. The following is an example:

Use kubectl to access the cluster. For details, see Accessing a Cluster Using kubectl.

Create a YAML file named ingress-test.yaml. The file name can be customized.

vi ingress-test.yaml

An example YAML file of an ingress associated with an existing load balancer is as follows:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: test-rewrite-url
  namespace: default
  annotations:
    kubernetes.io/elb.id: df76342f-e898-402a-bac8-bde5bf974da8
    kubernetes.io/elb.class: performance
    kubernetes.io/elb.port: '80'
    kubernetes.io/elb.rewrite-target: /$1/$2       # Rewrite path
spec:
  rules:
    - host: "example.com"
      http:
        paths:
          - path: /first/(.*)/(.*)/end      # This path will be rewritten.
            backend:
              service:
                name: test-service
                port:
                  number: 80
            property:
              ingress.beta.kubernetes.io/url-match-mode: REGEX
            pathType: ImplementationSpecific
  ingressClassName: cce

**Table 1** Key parameters
Parameter	Mandatory	Type	Description
kubernetes.io/elb.rewrite-target	Yes	String	Information about the rewritten path. Format: A proper rule matching a regular expression must start with a slash (/). Parameter: This configuration takes effect on the URL of a single ingress matching the regular expression. After the configuration is deleted, the target URL rewriting rule will be automatically cleared. Either this annotation or the annotation of a grayscale release can be configured.

Create an ingress.
```
kubectl create -f ingress-test.yaml
```
If information similar to the following is displayed, the ingress has been created:
```
ingress/test-rewrite-url created
```

Check the created ingress.

kubectl get ingress

If information similar to the following is displayed, the ingress has been created:

NAME              CLASS    HOSTS     ADDRESS          PORTS   AGE
test-rewrite-url  cce      *         121.**.**.**     80      10s

Use curl to verify the rewriting, where ${ELB_IP} is the IP address accessed by the target ingress.
```
# curl -H "Host:example.com" ${ELB_IP}/first/aaa/bbb/end
```
The access path will be rewritten to /aaa/bbb.