Set up URL rewrite for a classic Application Load Balancer

This example demonstrates rewriting the path specified in a request for a classic Application Load Balancer.

To configure traffic management for global external Application Load Balancers and regional external Application Load Balancers, see the following pages:

• Setting up traffic management for global external Application Load Balancer
• Setting up traffic management for regional external Application Load Balancer

Before you begin

• Read about URL rewrites.

• Read about URL maps in general and path matchers in particular.

• The URL rewrite example assumes that you've already created your external Application Load Balancer following the steps outlined in Setting up a load balancer with Cloud Storage buckets.

  That example leads you through the creation of two resources:

  • http://IP_ADDRESS/never-fetch/three-cats.jpg
  • http://IP_ADDRESS/love-to-fetch/two-dogs.jpg

  Where /never-fetch/three-cats.jpg is stored in /cats, which is the default service, and /love-to-fetch/two-dogs.jpg is stored in /dogs.

  At this point, the URL map looks like this:

  gcloud compute url-maps describe http-lb
  

  creationTimestamp: '2020-10-13T11:18:10.561-07:00'
  defaultService: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/cats
  fingerprint: MKfYsObzqgw=
  hostRules:
  - hosts:
    - '*'
    pathMatcher: path-matcher-1
  id: '1420501688756228493'
  kind: compute#urlMap
  name: test-bucket
  pathMatchers:
  - defaultService: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/cats
    name: path-matcher-1
    pathRules:
    - paths:
      - /love-to-fetch/*
      service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/dogs
  selfLink: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/urlMaps/http-lb
  

Modifying the URL map

Important: The rewrite is prepended to the path as is. Full path rewrites are not supported. External Application Load Balancers only implement path prefix rewrites. For example, you can rewrite: host.name/path1/resource1 to host.name/path2/resource1. You cannot rewrite host.name/path1/resource1 to host.name/path1/resource2.

In this example, you rewrite the /love-to-fetch/ URL so that users can reach the two-dogs.jpg image with this simplified URL:

• http://IP_ADDRESS/two-dogs.jpg

To do this, modify the load balancer's URL map as follows:

Console

Edit your load balancer

1. Go to the Load balancing page in the Google Cloud console.
   Go to the Load balancing page
2. Click http-lb.
3. Click Edit .
4. Keep the window open to continue.

Change the host and path rules

1. In the left column of the screen, click Host and path rules.
2. Select Advanced host and path rule (URL redirect, URL rewrite).
3. Click the row that contains the non-default path rule, in this case, the row that has an asterisk (*) for all hosts.
4. Click the pencil icon for the /love-to-fetch/* Route traffic to a single backend: dogs row.
5. Under Paths, delete /love-to-fetch/* and add /*.
6. Under Action, select Route traffic to a single backend.
7. Click Add-on action (URL rewrite).
8. Leave Host rewrite blank.
9. Under Path prefix rewrite, enter /love-to-fetch/.
10. Under Backend, select dogs.
11. Click Save.

12. Click Done. The new host and path rule looks as follows:

    Paths	Action	Backend
    Any unmatched (default)	Route traffic to a single backend	cats
    /*	Route traffic to a single backend	dogs

13. If everything looks correct, click Update to update your HTTP load balancer.

gcloud

1. Create a YAML file /tmp/http-lb.yaml, making sure to substitute PROJECT_ID with your project ID.

   When a user requests path /*, the path gets rewritten in the backend to the actual location of the content, which is /love-to-fetch/*.

   defaultService: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/cats
   hostRules:
   - hosts:
     - '*'
     pathMatcher: path-matcher-1
   name: http-lb
   pathMatchers:
   - defaultService: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/cats
     name: path-matcher-1
     pathRules:
     - paths:
       - /*
       routeAction:
         urlRewrite:
           pathPrefixRewrite: /love-to-fetch/
       service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/dogs
   tests:
   - description: Test routing to backend bucket, dogs
     host: example.com
     path: /love-to-fetch/test
     service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/dogs
   

2. Validate the URL map.

   gcloud compute url-maps validate --source /tmp/http-lb.yaml
   

   If the tests pass and the command outputs a success message, save the changes to the URL map.

3. Update the URL map.

   gcloud compute url-maps import http-lb \
      --source /tmp/http-lb.yaml \
      --global
   

Testing

Note the IPv4 address that was reserved:

gcloud compute addresses describe example-ip \
    --format="get(address)" \
    --global

After waiting several minutes for the changes to propagate, you can test this setup.

On the command line, run the following curl command:

curl http://IP_ADDRESS/two-dogs.jpg

In a browser, open http://IP_ADDRESS/two-dogs.jpg.

What's next

• Clean up the load balancer setup.