Set up traffic management for global external Application Load Balancers

This document shows examples of using traffic management for some specific use cases. Many other use cases are possible.

The document contains examples for global external Application Load Balancers. Global external Application Load Balancers use the EXTERNAL_MANAGED load balancing scheme and global load balancing components, such as the forwarding rule, URL map, and backend service.

For information about traffic management with a classic Application Load Balancer, see Traffic management overview for a classic Application Load Balancer.

For information about traffic management with regional external Application Load Balancers, see Traffic management overview for regional external Application Load Balancers.

In addition to the advanced routing features described on this page, certain Application Load Balancers integrate with Service Extensions to let you inject custom logic into the load balancing data path by configuring Service Extensions callouts.

Before you begin

Make sure that you understand how traffic management works. For more information, read Traffic management overview for global external Application Load Balancers.

Configure and test traffic management

Within your chosen configuration environment, you set up traffic management by using YAML configurations. A URL map and a backend service each has its own YAML file. Depending on your desired functionality, you need to write either a URL map YAML file, a backend service YAML file, or both.

For help writing these YAML files, you can use the examples on this page and the Cloud Load Balancing API documentation.

The Google Cloud console is not supported.

The global URL map API and the global backend service API documentation provides a full list of fields, including semantics regarding relationships, restrictions, and cardinality.

You can add configuration tests to a URL map to ensure that your URL map routes requests as intended. You can experiment with different URL map rules and run as many tests as needed to be confident that the map routes traffic to the appropriate backend service or backend bucket. For details, see Add tests to a URL map. If you want to test new changes to a URL map without actually deploying the map, see Validate the URL map configuration.

Map traffic to a single service

Send all traffic to a single service. Make sure to replace the placeholders.

    defaultService: global/backendServices/BACKEND_SERVICE_1
    hostRules:
    - hosts:
      - '*'
      pathMatcher: matcher1
    name: URL_MAP_NAME
    pathMatchers:
    - defaultService: global/backendServices/BACKEND_SERVICE_1
      name: matcher1
      routeRules:
      - matchRules:
        - prefixMatch: /PREFIX
        priority: PRIORITY  # 0 is highest
        routeAction:
          weightedBackendServices:
          - backendService: global/backendServices/BACKEND_SERVICE_1
            weight: 100

Split traffic between two services

Split traffic between two or among multiple services. Make sure to replace the placeholders.

   defaultService: global/backendServices/BACKEND_SERVICE_1
   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   name: URL_MAP_NAME
   pathMatchers:
   - defaultService: global/backendServices/BACKEND_SERVICE_1
     name: matcher1
     routeRules:
     - matchRules:
       - prefixMatch: /PREFIX
       priority: 2
       routeAction:
         weightedBackendServices:
         - backendService: global/backendServices/BACKEND_SERVICE_1
           weight: 95
         - backendService: global/backendServices/BACKEND_SERVICE_2
           weight: 5

Configure a URL redirect

The following example returns a configurable 3xx response code. The example also sets the Location response header with the appropriate URI, replacing the host and path as specified in the redirect action.

   defaultService: global/backendServices/BACKEND_SERVICE_1
   name: global-lb-map
   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   pathMatchers:
   - defaultService: global/backendServices/BACKEND_SERVICE_1
     name: matcher1
     routeRules:
       - matchRules:
           - prefixMatch: /PREFIX
         priority: PRIORITY  # 0 is highest
         urlRedirect:
           hostRedirect: "new-host-name.com" # Omit to keep the requested host
           pathRedirect: "/new-path" # Omit to keep the requested path; mutually exclusive to prefixRedirect
           prefixRedirect: "/newPrefix" # Omit to keep the requested path; mutually exclusive to pathRedirect
           redirectResponseCode: FOUND
           stripQuery: True

Mirror traffic

In addition to forwarding the request to the selected backend service, you can send an identical request to the configured mirror backend service on a fire and forget basis. The load balancer doesn't wait for a response from the backend to which it sends the mirrored request. Mirroring is useful for testing a new version of a backend service. You can also use it to debug production errors on a debug version of your backend service, rather than on the production version.

   defaultService: global/backendServices/BACKEND_SERVICE_1
   name: global-lb-map
   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   pathMatchers:
   - defaultService: global/backendServices/BACKEND_SERVICE_1
     name: matcher1
     routeRules:
       - matchRules:
           - prefixMatch: /PREFIX
         priority: PRIORITY  # 0 is highest
         routeAction:
           weightedBackendServices:
             - backendService: global/backendServices/BACKEND_SERVICE_1
               weight: 100
           requestMirrorPolicy:
             backendService: global/backendServices/BACKEND_SERVICE_2

Traffic mirroring is only supported in the following cases:

• Both backend services have instance group backends. Other backend types are not supported.
• HTTP requests don't have bodies.

Mirroring can't be configured for only a specific portion of requests. Even if you split traffic between multiple weighted backend services, the mirror backend service receives all the requests. However, you can use custom headers to record which backend service was used to serve the original request. The following example adds a custom header called x-weighted-picked-backend to all client requests. For the header value, use the name of the backend service that served the original request.

   defaultService: global/backendServices/BACKEND_SERVICE_1
   name: global-lb-map
   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   pathMatchers:
   - defaultService: global/backendServices/BACKEND_SERVICE_1
     name: matcher1
     routeRules:
       - matchRules:
           - prefixMatch: /PREFIX
         priority: PRIORITY  # 0 is highest
         routeAction:
           weightedBackendServices:
            - backendService: global/backendServices/BACKEND_SERVICE_1
              weight: 95
              headerAction:
                requestHeadersToAdd:
                - headerName: x-weighted-picked-backend
                  headerValue: BACKEND_SERVICE_1
                  replace: True
            - backendService: global/backendServices/BACKEND_SERVICE_2
              weight: 5
              headerAction:
                requestHeadersToAdd:
                - headerName: x-weighted-picked-backend
                  headerValue: BACKEND_SERVICE_2
                  replace: True
           requestMirrorPolicy:
             backendService: global/backendServices/BACKEND_SERVICE_3

Rewrite the requested URL

Rewrite the host name portion of the URL, the path portion of the URL, or both, before sending a request to the selected backend service. Make sure to replace the placeholders.

   defaultService: global/backendServices/BACKEND_SERVICE_1
   name: global-lb-map
   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   pathMatchers:
   - defaultService: global/backendServices/BACKEND_SERVICE_1
     name: matcher1
     routeRules:
       - matchRules:
           - prefixMatch: /PREFIX
         priority: PRIORITY  # 0 is highest
         routeAction:
           weightedBackendServices:
             - backendService: global/backendServices/BACKEND_SERVICE_1
               weight: 100
           urlRewrite:
             hostRewrite: "new-host-name.com" # Omit to keep the requested host
             pathPrefixRewrite: "/new-path/" # Omit to keep the requested path

Retry a request

Configure the conditions under which the load balancer retries failed requests, how long the load balancer waits before retrying, and the maximum number of retries permitted.

   defaultService: global/backendServices/BACKEND_SERVICE_1
   name: global-lb-map
   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   pathMatchers:
   - defaultService: global/backendServices/BACKEND_SERVICE_1
     name: matcher1
     routeRules:
       - matchRules:
           - prefixMatch: /PREFIX
         priority: PRIORITY  # 0 is highest
         routeAction:
           weightedBackendServices:
             - backendService: global/backendServices/BACKEND_SERVICE_1
               weight: 100
           retryPolicy:
             retryConditions: 502, 504
             numRetries: 3
             perTryTimeout:
               seconds: 1
               nanos: 500000000

Specify the route timeout

Specify the timeout for the selected route. Timeout is computed from the time the request is fully processed until the response is fully processed. Timeout includes all retries. Make sure to replace the placeholders.

   defaultService: global/backendServices/BACKEND_SERVICE_1
   name: global-lb-map
   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   pathMatchers:
   - defaultService: global/backendServices/BACKEND_SERVICE_1
     name: matcher1
     routeRules:
       - matchRules:
           - prefixMatch: /PREFIX
         priority: PRIORITY  # 0 is highest
         routeAction:
           weightedBackendServices:
             - backendService: global/backendServices/BACKEND_SERVICE_1
               weight: 100
           timeout:
             seconds: 30
             nanos: 0

Configure fault injection

Introduce errors when servicing requests to simulate failures, including high latency, service overload, service failures, and network partitioning. This feature is useful for testing the resiliency of a service to simulated faults.

   defaultService: global/backendServices/BACKEND_SERVICE_1
   name: global-lb-map
   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   pathMatchers:
   - defaultService: global/backendServices/BACKEND_SERVICE_1
     name: matcher1
     routeRules:
       - matchRules:
           - prefixMatch: /PREFIX
         priority: PRIORITY  # 0 is highest
         routeAction:
           weightedBackendServices:
             - backendService: global/backendServices/BACKEND_SERVICE_1
               weight: 100
           faultInjectionPolicy:
             delay:
               fixedDelay:
                 seconds: 10
                 nanos: 0
               percentage: 25
             abort:
               httpStatus: 503
               percentage: 50

Configure CORS

Configure cross-origin resource sharing (CORS) policies to handle settings for enforcing CORS requests.

   defaultService: global/backendServices/BACKEND_SERVICE_1
   name: global-lb-map
   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   pathMatchers:
   - defaultService: global/backendServices/BACKEND_SERVICE_1
     name: matcher1
     routeRules:
       - matchRules:
           - prefixMatch: /PREFIX
         priority: PRIORITY  # 0 is highest
         routeAction:
           weightedBackendServices:
             - backendService: global/backendServices/BACKEND_SERVICE_1
               weight: 100
           corsPolicy:
               allowOrigins: [ "http://my-domain.com" ]
               allowMethods: [ "GET", "POST" ]
               allowHeaders: [ "Authorization", "Content-Type" ]
               maxAge: 1200
               allowCredentials: true

Add and remove request and response headers

Note: We announced a change in behavior for custom headers configured on URL maps and backend services. This change does not affect projects that had existing traffic that used custom headers before November 14, 2022. For details, see the release note for November 14, 2022.

Add and remove request headers before sending a request to the backend service. Also add and remove response headers after receiving a response from the backend service.

There are restrictions on valid values for headerName and headerValue. For details, see How custom headers work.

   defaultService: global/backendServices/BACKEND_SERVICE_1
   name: global-lb-map
   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   pathMatchers:
   - defaultService: global/backendServices/BACKEND_SERVICE_1
     name: matcher1
     routeRules:
       - matchRules:
           - prefixMatch: /PREFIX
         priority: PRIORITY  # 0 is highest
         routeAction:
           weightedBackendServices:
             - backendService: global/backendServices/BACKEND_SERVICE_1
               headerAction:
                 requestHeadersToAdd:
                 - headerName: header-1-name
                   headerValue: header-1-value
                   replace: True
                 requestHeadersToRemove:
                 - header-2-name
                 - header-3-name
                 responseHeadersToAdd:
                 - headerName: header-4-name
                   headerValue: header-4-value
                   replace: True
                responseHeadersToRemove:
                - header-5-name
                - header-6-name

Configure outlier detection

Specify the criteria for eviction of unhealthy backend VMs or endpoints in NEGs, along with criteria defining when a backend or endpoint is considered healthy enough to receive traffic again. Make sure to replace the placeholders.

    loadBalancingScheme: EXTERNAL_MANAGED
    localityLbPolicy: RANDOM
    name: global/backendServices/BACKEND_SERVICE_1
    outlierDetection:
      baseEjectionTime:
        nanos: 0
        seconds: 30
      consecutiveErrors: 5
      consecutiveGatewayFailure: 3
      enforcingConsecutiveErrors: 2
      enforcingConsecutiveGatewayFailure: 100
      enforcingSuccessRate: 100
      interval:
        nanos: 0
        seconds: 1
      maxEjectionPercent: 50
      successRateMinimumHosts: 5
      successRateRequestVolume: 100
      successRateStdevFactor: 1900

Set up traffic splitting: detailed steps

Note: Don't configure session affinity if you're using weighted traffic splitting. If you do, the weighted traffic splitting configuration takes precedence.

This example demonstrates the following steps:

1. Create distinct templates for different services.

2. Create instance groups for those templates.

3. Create routing rules that set up 95% / 5% traffic splitting.

4. Send curl commands showing that the traffic split percentages roughly match the configuration.

These instructions assume the following:

• A target proxy and forwarding rule have been created, along with a URL map named global-lb-map.

• The URL map sends all traffic to one backend service, called red-service, which is the default backend service.

• You set up an alternate path that sends 5% of the traffic to blue-service and 95% of traffic to green-service.

• A path matcher is used.

• You are using Cloud Shell or another environment with bash installed.

Define the services

The following bash function creates a backend service, including the instance template and the managed instance group.

These instructions assume that an HTTP health check (global-lb-basic-check) has been created. For instructions, see one of the following pages:

• Setting up a global external Application Load Balancer with a Compute Engine backend
• Setting up a global external Application Load Balancer with a backend bucket
• Setting up a global external Application Load Balancer with hybrid connectivity
• Setting up a global external Application Load Balancer with with Cloud Run, App Engine, or Cloud Functions

function make_service() {
  local name="$1"
  local region="$2"
  local zone="$3"
  local network="$4"
  local subnet="$5"
  local subdir="$6"

  www_dir="/var/www/html/$subdir"

  (set -x; \
  gcloud compute instance-templates create "${name}-template" \
    --region="$region" \
    --network="$network" \
    --subnet="$subnet" \
    --tags=allow-ssh,load-balanced-backend \
    --image-family=debian-10 \
    --image-project=debian-cloud \
    --metadata=startup-script="#! /bin/bash
  apt-get update
  apt-get install apache2 -y
  a2ensite default-ssl
  a2enmod ssl
  sudo mkdir -p $www_dir
  /bin/hostname | sudo tee ${www_dir}index.html
  systemctl restart apache2"; \
  gcloud compute instance-groups managed create \
    "${name}-instance-group" \
    --zone="$zone" \
    --size=2 \
    --template="${name}-template"; \
  gcloud compute backend-services create "${name}-service" \
    --load-balancing-scheme=EXTERNAL_MANAGED \
    --protocol=HTTP \
    --health-checks=global-lb-basic-check \
    --global \
  gcloud compute backend-services add-backend "${name}-service" \
    --balancing-mode='UTILIZATION' \
    --instance-group="${name}-instance-group" \
    --instance-group-zone="$zone" \
    --global)
}

Create the services

Call the function to make three services, red, green, and blue. The red service acts as the default service for requests to /. The green and blue services are both set up on /prefix to handle 95% and 5% of the traffic, respectively.

make_service red us-west1 us-west1-a lb-network backend-subnet ""
make_service green us-west1 us-west1-a lb-network backend-subnet /prefix
make_service blue us-west1 us-west1-a lb-network backend-subnet /prefix

Create the URL map

Console

1. Go to the Load balancing page in the Google Cloud console.
   Go to Load balancing
2. Click the global-lb-map link.
3. Click Edit .

Configure the new routing rules

1. Under Routing rules, select Advanced host, path and route rule.
2. Under New hosts and path matcher, create the default action by setting the Service to red-service.
3. Click Done.
4. Click Add hosts and path matcher.
5. In the Hosts field, enter the IP address of your load balancer's forwarding rule.

6. Paste the following YAML content into the Path matcher box:

   defaultService: global/backendServices/red-service
   name: matcher1
   routeRules:
   - priority: 2
     matchRules:
       - prefixMatch: /PREFIX
     routeAction:
       weightedBackendServices:
         - backendService: global/backendServices/green-service
           weight: 95
         - backendService: global/backendServices/blue-service
           weight: 5
   

7. Click Done.

8. Click Update.

gcloud

1. Export the existing URL map using the gcloud compute url-maps export command:

   gcloud compute url-maps export global-lb-map \
     --destination=global-lb-map-config.yaml \
     --global
   

2. Update the URL map file global-lb-map-config.yaml by adding this to the end of the file:

   hostRules:
   - hosts:
     - '*'
     pathMatcher: matcher1
   pathMatchers:
   - defaultService: global/backendServices/red-service
     name: matcher1
     routeRules:
     - priority: 2
       matchRules:
         - prefixMatch: /PREFIX
       routeAction:
         weightedBackendServices:
           - backendService: global/backendServices/green-service
             weight: 95
           - backendService: global/backendServices/blue-service
             weight: 5
   

3. Update the URL map using the gcloud compute url-maps import command:

   gcloud compute url-maps import global-lb-map \
      --global \
      --source=global-lb-map-config.yaml
   

Test the configuration

To test the configuration, first ensure that requests to the load balancer's IP address set up earlier are handled by the default red configuration.

Then check to make sure that requests sent to FORWARDING_RULE_IP_ADDRESS/prefix are split as expected.

Set up session affinity based on HTTP_COOKIE

Traffic control enables you to configure session affinity based on a provided cookie. To configure HTTP_COOKIE based session affinity for a backend service named red-service, follow these directions.

1. Use the gcloud compute backend_services export command to get the backend service configuration.

   gcloud compute backend-services export red-service \
       --destination=red-service-config.yaml \
       --global
   

2. Update the red-service-config.yaml file as follows:

   sessionAffinity: 'HTTP_COOKIE'
   localityLbPolicy: 'RING_HASH'
   consistentHash:
    httpCookie:
     name: 'http_cookie'
     path: '/cookie_path'
     ttl:
       seconds: 100
       nanos: 0
    minimumRingSize: 10000
   

3. In the red-service-config.yaml file, delete the following line:

   sessionAffinity: NONE
   

4. Update the backend service configuration file:

   gcloud compute backend-services import red-service \
       --source=red-service-config.yaml \
       --global
   

Troubleshooting

Use this information for troubleshooting when traffic is not being routed according to the route rules and traffic policies that you configured.

For information about logging and monitoring, see External HTTP(S) logging and monitoring.

Symptoms:

• Increased traffic to services in rules above the rule in question.
• An unexpected increase in 4xx and 5xx HTTP responses for a given route rule.

Solution: Check the order of your route rules. Route rules are interpreted in the order in which they are specified.

Route rules within a URL map are interpreted in the order in which they are specified. This is different from the way that path rules are interpreted by longest prefix match. For a path rule, the global external Application Load Balancer only selects a single path rule; however, when you use route rules, more than one might apply.

When you define route rules, check to be sure that rules at the top of the list do not inadvertently route traffic that would otherwise have been routed by a subsequent route rule. The service that receives misdirected traffic would likely reject requests, and the service in your route rules would receive reduced traffic or no traffic at all.

What's next

• Clean up the load balancer setup.