Upgrade a GCP instance group to dual-stack, without restarting/recreating the instances

in-place-dualstack-upgrade.sh

# Steps to switch a GCE pool from single-stack IPv4 to dual-stack.
#
# These steps avoid recreating VMs in a pool; it happens in-place.

# Step 1: Switch all existing VMs in the pool
#  (run once per instance in the group)
curl --request PATCH \
  'https://compute.googleapis.com/compute/v1/projects/my-project/zones/europe-west1-b/instances/instance-1234/updateNetworkInterface?networkInterface=nic0' \
  --header "Authorization: Bearer $(gcloud auth print-access-token)" \
  --header 'Accept: application/json' \
  --header 'Content-Type: application/json' \
  --data '{"stackType":"IPV4_IPV6"}' \
  --compressed

# Step 2: Create a new instance template using the existing one. Only change the stackType field!
#  List the original instance template properties with:
#  gcloud compute instance-templates describe my-instancegroup-1 --format=json
curl --request POST \
  'https://compute.googleapis.com/compute/v1/projects/my-project/global/instanceTemplates' \                                                                   
  --header "Authorization: Bearer $(gcloud auth print-access-token)" \
  --header 'Accept: application/json' \
  --header 'Content-Type: application/json' \
  --data '{"description":"my instancepool","name":"my-instance-template-20230811","properties":{"canIpForward":false,"disks":[{"autoDelete":true,"boot":true,"deviceName":"my-instancegroup-1-20230722121021","initializeParams":{"diskSizeGb":"300","diskType":"pd-standard","sourceImage":"https://www.googleapis.com/compute/v1/projects/my-project-2/global/images/gceimage-focal-2023-07-21t13-05-58z"},"mode":"READ_WRITE","type":"PERSISTENT"}],"labels":{},"machineType":"e2-standard-4","metadata":{"fingerprint":"LbTYUonF2cc=","items":[]},"networkInterfaces":[{"accessConfigs":[{"name":"External NAT","networkTier":"PREMIUM","type":"ONE_TO_ONE_NAT"}],"stackType":"IPV4_IPV6","network":"https://www.googleapis.com/compute/v1/projects/my-project/global/networks/vpc-1","nicType":"GVNIC","subnetwork":"https://www.googleapis.com/compute/v1/projects/my-project/regions/europe-west1/subnetworks/ipv6-gua-subnet-1"}],"scheduling":{"automaticRestart":true,"onHostMaintenance":"MIGRATE","preemptible":false,"provisioningModel":"STANDARD"},"serviceAccounts":[{"email":"[email protected]","scopes":["https://www.googleapis.com/auth/cloud-platform","https://www.googleapis.com/auth/userinfo.email"]}],"tags":{"items":[]}}}' \
  --compressed

# Step 3: Switch the instanceGroupManager to the new template
curl --request POST \
  'https://compute.googleapis.com/compute/v1/projects/my-project/regions/europe-west1/instanceGroupManagers/my-instancegroup-1/setInstanceTemplate' \
  --header "Authorization: Bearer $(gcloud auth print-access-token)" \
  --header 'Accept: application/json' \
  --header 'Content-Type: application/json' \
  --data '{"instanceTemplate":"https://www.googleapis.com/compute/v1/projects/my-project/global/instanceTemplates/my-instance-template-20230811"}' \
  --compressed

# Step 4: Trigger the upgrade
curl --request POST \
  'https://compute.googleapis.com/compute/v1/projects/my-project/regions/europe-west1/instanceGroupManagers/my-instancegroup-1/applyUpdatesToInstances' \
  --header "Authorization: Bearer $(gcloud auth print-access-token)" \
  --header 'Accept: application/json' \
  --header 'Content-Type: application/json' \
  --data '{"allInstances":true,"mostDisruptiveAllowedAction":"REFRESH"}' \
  --compressed