GCP traffic splitting across external services in url map error: "One of backend_service or url_redirect must be set"

Question

First of all, I have an internet network endpoint group (NEG):

gcloud compute network-endpoint-groups update [neg-name] \
    --add-endpoint="fqdn=[service.example.com],port=443" \
    --global

This is what's called "Global external HTTP(S) load balancer (classic)" in the Backend Service documentation.

I have two services, created like this:

gcloud beta compute backend-services create [service-name] \
        --load-balancing-scheme=EXTERNAL \
        --protocol=HTTPS \
        --port-name=https \
        --enable-logging \
        --logging-sample-rate=1 \
        --global

gcloud beta compute backend-services add-backend [service-name] \
       --network-endpoint-group=[neg-name] \
       --global-network-endpoint-group \
       --global \
       --custom-request-header="Host: service.example.com" # Fix SSL issue

I also have a url map, created like this:

gcloud beta compute url-maps create [url-map-name] \
        --default-service [service 1 name]

I want to create a traffic splitting rule that routes traffic between service 1 and service 2. Following the load balancing docs, I came up with this:

creationTimestamp: '2021-11-26T12:41:59.779-08:00'
defaultService: https://www.googleapis.com/compute/beta/projects/[project-name]/global/backendServices/[service 1 name]
fingerprint: [fingerprint]
hostRules:
- hosts:
  - '*'
  pathMatcher: default-matcher
id: [id]
kind: compute#urlMap
name: [url-map-name]
pathMatchers:
- defaultService: https://www.googleapis.com/compute/beta/projects/[project-name]/global/backendServices/[service 1 name]
  name: default-matcher
  routeRules:
  - priority: 1
    matchRules:
      - prefixMatch: '/'
    routeAction:
      weightedBackendServices:
        - weight: 50
          backendService: https://www.googleapis.com/compute/beta/projects/[project-name]/global/backendServices/[service 2 name]
        - weight: 50
          backendService: https://www.googleapis.com/compute/beta/projects/[project-name]/global/backendServices/[service 1 name]
selfLink: https://www.googleapis.com/compute/beta/projects/[project-name]/global/urlMaps/[url-map-name]

When I try to edit the url map with the above configuration, the following error is returned (debugger breakpoints included in output):

$ gcloud beta compute url-maps edit [url-map-name] --global --verbosity=debug
DEBUG: Running [gcloud.beta.compute.url-maps.edit] with arguments: [--global: "True", --verbosity: "debug", URL_MAP: "[url-map-name]"]
INFO: Display format: "default"
DEBUG: Starting new HTTPS connection (1): compute.googleapis.com:443
DEBUG: https://compute.googleapis.com:443 "POST /batch/compute/beta HTTP/1.1" 200 None
> /opt/google-cloud-sdk/lib/surface/compute/url_maps/edit.py(100)_ProcessEditedResource()
-> return holder.client.MakeRequests(
(Pdb) c
DEBUG: https://compute.googleapis.com:443 "POST /batch/compute/beta HTTP/1.1" 200 None
> /opt/google-cloud-sdk/lib/googlecloudsdk/api_lib/compute/batch_helper.py(117)MakeRequests()
-> error_message = None
(Pdb) c
> /opt/google-cloud-sdk/lib/googlecloudsdk/api_lib/compute/client_adapter.py(116)MakeRequests()
-> utils.RaiseToolException(errors, error_message="Could not fetch resource:")
(Pdb) errors
[(400, 'Invalid value for field \'resource\': \'{  "name": "[url-map-name]",  "hostRule": [{    "host": ["*"],    "pathMatcher": "default-matcher...\'. One of backend_service or url_redirect must be set')]
(Pdb) c
There was a problem applying your changes: Could not fetch resource:
 - Invalid value for field 'resource': '{  "name": "[url-map-name]",  "hostRule": [{    "host": ["*"],    "pathMatcher": "default-matcher...'. One of backend_service or url_redirect must be
 set

Would you like to edit the resource again? (Y/n)?  n

Validating (Thank you Alex G):

$ gcloud beta compute url-maps validate --source=url-map-traffic-splitting.yml --global --verbosity=debug
DEBUG: Running [gcloud.beta.compute.url-maps.validate] with arguments: [--global: "True", --source: "url-map-traffic-splitting.yml", --verbosity: "debug"]
DEBUG: Starting new HTTPS connection (1): compute.googleapis.com:443
DEBUG: https://compute.googleapis.com:443 "POST /compute/beta/projects/[project-name]/global/urlMaps/[url-map-name]/validate?alt=json HTTP/1.1" 200 None
INFO: Display format: "default"
result:
  loadErrors:
  - One of backend_service or url_redirect must be set
  loadSucceeded: false
  testPassed: false
DEBUG: SDK update checks are disabled.

What I've tried:

Tried with pathRules instead of routeRules, it works and the url map is updated.

I tried hacking the gcloud libraries to give better errors - but the error is returned by the API, not the client:

HttpError accessing : response: <{'Content-Type': 'application/json; charset=UTF-8', 'Vary': 'Origin', 'status': '400'}>, content <{
  "error": {
    "code": 400,
    "message": "Invalid value for field 'resource': '{  \"name\": \"[url-map-name]\",  \"hostRule\": [{    \"host\": [\"*\"],    \"pathMatcher\": \"default-matcher...'. One of backend_service or url_redirect must be set",
    "errors": [
      {
        "message": "Invalid value for field 'resource': '{  \"name\": \"[url-map-name]\",  \"hostRule\": [{    \"host\": [\"*\"],    \"pathMatcher\": \"default-matcher...'. One of backend_service or url_redirect must be set",
        "domain": "global",
        "reason": "invalid"
      }
    ]
  }
}

I've searched the GCP documentation for any mentions of this error, or mentions of limits to what url maps can do, but found nothing.

GCP traffic splitting across external services in url map error: "One of backend_service or url_redirect must be set"

0 Answers