Set up URL rewrite for a classic Application Load Balancer

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

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

Before you begin

  • Read aboutURL rewrites.

  • Read aboutURL maps in general andpath matchersin particular.

  • The URL rewrite example assumes that you've already created yourexternal Application Load Balancer following the steps outlined inSetting up a load balancerwith Cloud Storagebuckets.

    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 isthe 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/catsfingerprint:MKfYsObzqgw=hostRules:-hosts:-'*'pathMatcher:path-matcher-1id:'1420501688756228493'kind:compute#urlMapname:test-bucketpathMatchers:-defaultService:https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/catsname:path-matcher-1pathRules:-paths:-/love-to-fetch/*service:https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/dogsselfLink: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 arenot supported. External Application Load Balancers only implement path prefix rewrites. Forexample, youcan rewrite:host.name/path1/resource1 tohost.name/path2/resource1. Youcannot rewritehost.name/path1/resource1tohost.name/path1/resource2.

In this example, you rewrite the/love-to-fetch/ URL so that users can reach thetwo-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. Clickhttp-lb.
  3. ClickEdit.
  4. Keep the window open to continue.

Change the host and path rules

  1. In the left column of the screen, clickHost and path rules.
  2. SelectAdvanced host and path rule (URL redirect, URL rewrite).
  3. Click the row that contains the non-default path rule, in this case, therow 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. UnderPaths, delete/love-to-fetch/* and add/*.
  6. UnderAction, selectRoute traffic to a single backend.
  7. ClickAdd-on action (URL rewrite).
  8. LeaveHost rewrite blank.
  9. UnderPath prefix rewrite, enter/love-to-fetch/.
  10. UnderBackend, selectdogs.
  11. ClickSave.

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

    PathsActionBackend
    Any unmatched (default)Route traffic to a single backendcats
    /*Route traffic to a single backenddogs

  13. If everything looks correct, clickUpdate to update your HTTPload balancer.

gcloud

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

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

    defaultService:https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/catshostRules:-hosts:-'*'pathMatcher:path-matcher-1name:http-lbpathMatchers:-defaultService:https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/catsname:path-matcher-1pathRules:-paths:-/*routeAction:urlRewrite:pathPrefixRewrite:/love-to-fetch/service:https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendBuckets/dogstests:-description:Test routing to backend bucket, dogshost:example.compath:/love-to-fetch/testservice: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 thissetup.

On the command line, run the following curl command:

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

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

What's next

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Last updated 2025-12-15 UTC.