Set up header and query parameter-based routing for the classic Application Load Balancer

This page includes two examples for classic Application Load Balancer:

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

Before you begin

Set up query parameter-based routing

This example demonstrates using query parameters to do A/B testing by matching on the query string.

Add two backend instance groups

For routing to be useful, you must have multiple backends.

To set up two backends, your VMs need to be in two instance groups. This guide describes how to create managed instance groups with Linux VMs that have Apache running and then set up load balancing.

The managed instance groups provide VMs running the backend servers of an external HTTP load balancer. For demonstration purposes, backends serve their own hostnames.

For simplicity, the backends reside in the same region. If you want a multi-region setup, you must have an instance template setup for the second region.

Console

  1. Create an instance template. In the Google Cloud console, go to the Instance templates page.

    Go to Instance templates

    1. Click Create instance template.
    2. For Name, enter lb-backend-template.
    3. Ensure that the Boot disk is set to a Debian image, such as Debian GNU/Linux 12 (bookworm). These instructions use commands that are only available on Debian, such as apt-get.
    4. Click Advanced options.
    5. Click Networking and configure the following field:
      1. For Network tags, enter allow-health-check.

    6. Click Management. Enter the following script into the Startup script field.

      #! /bin/bash
apt-get update
apt-get install apache2 -y
a2ensite default-ssl
a2enmod ssl
vm_hostname="$(curl -H "Metadata-Flavor:Google" \
http://metadata.google.internal/computeMetadata/v1/instance/name)"
echo "Page served from: $vm_hostname" | \
tee /var/www/html/index.html
systemctl restart apache2

    7. Click Create.

  2. Create a managed instance group. Go to the Instance groups page in the Google Cloud console.

    Go to Instance groups

    1. Click Create instance group.
    2. Select New managed instance group (stateless). For more information, see Stateless or stateful MIGs.
    3. For Name, enter first-example-ig.
    4. Under Location, select Single zone.
    5. For Region, select your preferred region. This example uses us-east1.
    6. For Zone, select us-east1-b.
    7. Under Instance template, select the instance template lb-backend-template.
    8. Under Maximum number of instances, enter 2.
    9. Under Autoscaling mode, select Off:do not autoscale.
    10. Click Create.

Create another managed instance group like this one. Name the second one second-example-ig, and base it on the lb-backend-template template.

gcloud

  1. Create an instance template.

    gcloud compute instance-templates create lb-backend-template \
   --region=us-east1 \
   --network=default \
   --subnet=default \
   --tags=allow-health-check \
   --image-family=debian-12 \
   --image-project=debian-cloud \
   --metadata=startup-script='#! /bin/bash
     apt-get update
     apt-get install apache2 -y
     a2ensite default-ssl
     a2enmod ssl
     vm_hostname="$(curl -H "Metadata-Flavor:Google" \
     http://metadata.google.internal/computeMetadata/v1/instance/name)"
     echo "Page served from: $vm_hostname" | \
     tee /var/www/html/index.html
     systemctl restart apache2'

  2. Create the first managed instance group based on the template.

    gcloud compute instance-groups managed create first-example-ig \
   --template=lb-backend-template --size=2 --zone=us-east1-b

  3. Create the second managed instance group based on the template.

    gcloud compute instance-groups managed create second-example-ig \
   --template=lb-backend-template --size=2 --zone=us-east1-c

Configuring a firewall rule

In this example, you create the fw-allow-health-check firewall rule. This is an ingress rule that allows traffic from the Google Cloud health checking systems (130.211.0.0/22 and 35.191.0.0/16). This example uses the target tag allow-health-check to identify the VMs.

Console

  1. In the Google Cloud console, go to the Firewall policies page.
    Go to Firewall policies
  2. Click Create firewall rule to create the second firewall rule:
  3. Enter a Name of fw-allow-health-check.
  4. Under Network, select Default.
  5. Under Targets, select Specified target tags.
  6. Populate the Target tags field with allow-health-check.
  7. Set Source filter to IPv4 ranges.
  8. Set Source IPv4 ranges to 130.211.0.0/22 and 35.191.0.0/16.
  9. Under Protocols and ports, select Specified protocols and ports.
  10. Select the TCP checkbox and enter 80 for the port numbers.
  11. Click Create.

gcloud 

gcloud compute firewall-rules create fw-allow-health-check \
    --network=default \
    --action=allow \
    --direction=ingress \
    --source-ranges=130.211.0.0/22,35.191.0.0/16 \
    --target-tags=allow-health-check \
    --rules=tcp

Reserving an external IP address

Now that your instances are up and running, set up a global static external IP address that your customers use to reach your load balancer.

Console

  1. Go to the External IP addresses page in the Google Cloud console.
    Go to the External IP addresses page
  2. Click Reserve static address to reserve an IPv4 address.
  3. Assign a Name of lb-ipv4-1.
  4. Set the Network tier to Standard.
  5. Set the IP version to IPv4.
  6. Set the Type to Global.
  7. Click Reserve.
  8. Ensure that the Type is set to Global.
  9. Click Reserve.

gcloud 

gcloud compute addresses create lb-ipv4-1 \
    --ip-version=IPV4 \
    --network-tier=PREMIUM \
    --global

Note the IPv4 address that was reserved:

gcloud compute addresses describe lb-ipv4-1 \
    --format="get(address)" \
    --global

Setting up the load balancer backends

Console

The Google Cloud console is currently unsupported for setting up header-based and parameter-based routing. Use gcloud or the API instead.

gcloud

  1. Create a health check. 
        gcloud compute health-checks create http http-basic-check \
        --port 80
  2. Create the first backend service.
    • For a global external Application Load Balancer, use the gcloud CLI command with load-balancing-scheme=EXTERNAL_MANAGED. This setting offers advanced traffic management capability.
    • For an classic Application Load Balancer, use load-balancing-scheme=EXTERNAL.
        gcloud compute backend-services create service-a \
        --load-balancing-scheme=LOAD_BALANCING_SCHEME \
        --global-health-checks \
        --protocol HTTP \
        --health-checks http-basic-check \
        --global
  3. Create the second backend service. 
        gcloud compute backend-services create service-b \
        --load-balancing-scheme=LOAD_BALANCING_SCHEME \
        --global-health-checks \
        --protocol HTTP \
        --health-checks http-basic-check \
        --global
  4. Add your first instance group as the backend to the first backend service. 
        gcloud compute backend-services add-backend service-a \
        --balancing-mode=UTILIZATION \
        --max-utilization=0.8 \
        --capacity-scaler=1 \
        --instance-group=first-example-ig \
        --instance-group-zone=us-east1-b \
        --global
  5. Add your second instance group as the backend to the second backend service. 
        gcloud compute backend-services add-backend service-b \
        --balancing-mode=UTILIZATION \
        --max-utilization=0.8 \
        --capacity-scaler=1 \
        --instance-group=second-example-ig \
        --instance-group-zone=us-east1-c \
        --global

Creating the URL map

Console

The Google Cloud console is currently unsupported for setting up header-based and parameter-based routing. Use gcloud or the API instead.

gcloud

  1. Create a YAML file /tmp/web-map-http.yaml. Replace PROJECT_ID with your project ID.

    defaultService: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-a
hostRules:
- hosts:
  - '*'
  pathMatcher: path-matcher-1
name: web-map-http
pathMatchers:
- defaultService: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-a
  name: path-matcher-1
  routeRules:
    - matchRules:
        - prefixMatch: /
          queryParameterMatches:
            - name: ABTest
              exactMatch: A
      priority: 0
      service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-a
    - matchRules:
        - prefixMatch: /
          queryParameterMatches:
            - name: ABTest
              exactMatch: B
      priority: 1
      service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-b
selfLink: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/urlMaps/web-map-http
tests:
- description: Test routing for query ABTest with A
  host: example.com
  path: /?ABTest=A
  service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-a
  expectedOutputUrl: http://example.com/?ABTest=A
- description: Test routing for query ABTest with B
  host: example.com
  path: /?ABTest=B
  service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-b
  expectedOutputUrl: http://example.com/?ABTest=B

  2. Validate the URL map.

    gcloud compute url-maps validate --source /tmp/web-map-http.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 web-map-http \
   --source /tmp/web-map-http.yaml \
   --global

Creating the target proxy and forwarding rule

Console

The Google Cloud console is currently unsupported for setting up header-based and parameter-based routing. Use gcloud or the API instead.

gcloud

  1. Create a target HTTP proxy to route requests to your URL map. 
        gcloud compute target-http-proxies create http-lb-proxy \
        --url-map web-map-http
  2. Create a global forwarding rule to route incoming requests to the proxy.
    • For a global external Application Load Balancer, use the gcloud CLI command with load-balancing-scheme=EXTERNAL_MANAGED. This setting offers advanced traffic management capability.
    • For an classic Application Load Balancer, use load-balancing-scheme=EXTERNAL.
        gcloud compute forwarding-rules create http-content-rule \
        --load-balancing-scheme=LOAD_BALANCING_SCHEME \
        --network-tier=PREMIUM \
        --address=lb-ipv4-1 \
        --global \
        --target-http-proxy=http-lb-proxy \
        --ports=80

Testing

Note the IPv4 address that was reserved:

gcloud compute addresses describe lb-ipv4-1 \
    --format="get(address)" \
    --global

Test this setup by running:

curl http://IP_ADDRESS?ABTest=A

curl http://IP_ADDRESS?ABTest=B

In a browser, open http://IP_ADDRESS?ABTest=A and http://IP_ADDRESS?ABTest=B.

Set up HTTP header-based routing

This example demonstrates adding and removing HTTP headers to do intelligent routing.

Before you begin

You can use an existing external Application Load Balancer or create a new one.

You can use this feature with any of the supported backend types. This example assumes that you're using VMs in an instance group.

To set up a simple load balancer, see the query parameter-based example above.

Updating the URL map

Console

The Google Cloud console is currently unsupported for setting up header-based and parameter-based routing. Use gcloud or the API instead.

gcloud

  1. This example demonstrates using HTTP request headers to do A/B testing by matching on values in the request's HTTP headers.

    Create a YAML file /tmp/web-map-http.yaml. Replace PROJECT_ID with your project ID.

    defaultService: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-a
kind: compute#urlMap
name: web-map-http
hostRules:
- hosts:
  - '*'
  pathMatcher: path-matcher-1
pathMatchers:
- defaultService: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-a
  name: path-matcher-1
  routeRules:
    - matchRules:
        - prefixMatch: /
          headerMatches:
            - headerName: ABTest
              exactMatch: A
      priority: 0
      service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-a
    - matchRules:
        - prefixMatch: /
          headerMatches:
            - headerName: ABTest
              exactMatch: B
      priority: 1
      service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-b
tests:
- description: Test routing for query ABTest with A
  host: example.com
  path: /
  headers:
  - name: ABTest
    value: A
  service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-a
- description: Test routing for query ABTest with B
  host: example.com
  path: /
  headers:
  - name: ABTest
    value: B
  service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices/service-b

  2. Validate the URL map.

    gcloud compute url-maps validate --source /tmp/web-map-http.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 web-map-http \
   --source /tmp/web-map-http.yaml \
   --global

Testing

Using the IPv4 address of the associated load balancer, test this setup by running:

curl http://IP_ADDRESS -H "ABTest: A"

curl http://IP_ADDRESS -H "ABTest: B"

What's next