googleapi: Error 400: Invalid value for field 'resource.network': 'projects/b/global/networks/c'. Network field cannot be modified., invalid

[chandra-scentre]

TL;DR

Have a Google Internal LB which got the backend.. it was created some 5 years back and now when i am trying to update the module version

Error when applying the module

Error updating RegionBackendService "projects/abc/regions/us-east1/backendServices/hc": googleapi: Error 400: Invalid value for field 'resource.network': 'projects/b/global/networks/c'. Network field cannot be modified., invalid

Expected behavior

No response

Observed behavior

module.abc.module.ilb.google_compute_region_backend_service.default will be updated in-place

~ resource "google_compute_region_backend_service" "default" {
~ connection_draining_timeout_sec = 0 -> 300
id = "projects/abc/regions/us-east1backendServices/ilb-with-http-hc"
name = "http-hc"
+ network = "https://www.googleapis.com/compute/v1/projects/xyzglobal/networks/abc"
# (17 unchanged attributes hidden)

    # (3 unchanged blocks hidden)
}

Plan: 0 to add, 1 to change, 0 to destroy.

Terraform Configuration

module "ilb" {
  source          = "GoogleCloudPlatform/lb-internal/google"
  version         = "7.0.0"
  name            = "ilb"
  region          = var.region
  ip_address      = google_compute_address.ilb.address
  ip_protocol     = "TCP"
  ports           = []
  all_ports       = true
  network         = var.host_network_name
  network_project = var.host_network_project_id
  subnetwork      = var.subnet_name
  health_check    = local.health_check
  source_tags     = ["${var.gce_prefix}-ingress"]
  target_tags     = [var.gce_prefix]
  backends = [
    { group = module.mig-a.instance_group, description = "worker-a" },
    { group = module.mig-b.instance_group, description = "worker-b" },
    { group = module.mig-c.instance_group, description = "worker-c" },
  ]
  service_label = "test"
}

Terraform Version

1.9.8

Additional information

when running the google describe command (note changed some project names and regions)

main thing to observe is that it is created in 2020 and there is no network in this describe .. now terraform module is trying to add the network module

gcloud compute backend-services describe http-hc
--region=us-east1
--project=abc
backends:

• balancingMode: CONNECTION
  description: worker-b
  group: https://www.googleapis.com/compute/v1/projects/def/regions/us-east1/instanceGroups/mig-b
• balancingMode: CONNECTION
  description: worker-a
  group: https://www.googleapis.com/compute/v1/projects/def/regions/us-east1/instanceGroups/mig-a
• balancingMode: CONNECTION
  description: worker-c
  group: https://www.googleapis.com/compute/v1/projects/def/regions/us-east1/instanceGroups/mig-c
  connectionDraining:
  drainingTimeoutSec: 0
  creationTimestamp: '2020-06-16T18:36:48.137-07:00'
  description: ''
  fingerprint: P1O2dKi-aWI=
  healthChecks:
• https://www.googleapis.com/compute/v1/projects/abc/global/healthChecks/hc
  id: 'mmmmm'
  kind: compute#backendService
  loadBalancingScheme: INTERNAL
  name: http-hc
  protocol: TCP
  region: https://www.googleapis.com/compute/v1/projects/abc/regions/us-east1
  selfLink: https://www.googleapis.com/compute/v1/projects/abc/regions/us-east1/backendServices/http-hc
  sessionAffinity: NONE
  timeoutSec: 10