- IPI cluster on GCP 
- Replaced a master node following the proccedure described here In Replacing an unhealthy etcd member whose machine is not running or whose node is not ready https://docs.openshift.com/container-platform/4.12/backup_and_restore/control_plane_backup_and_restore/replacing-unhealthy-etcd-member.html
- Provisioning the new machine using machine-api doesn't include the new provisioned virtual machine into the instance-group which is used for the endpoints of the API-INT load balancer at cloud provider

- Create a new master machine
$ cat new-master0-machine.yaml
apiVersion: machine.openshift.io/v1beta1
kind: Machine
metadata:
  annotations:
  finalizers:
  - machine.machine.openshift.io
  generation: 3
  labels:
    machine.openshift.io/cluster-api-cluster: case-03507533-rfctg
    machine.openshift.io/cluster-api-machine-role: master
    machine.openshift.io/cluster-api-machine-type: master
    machine.openshift.io/instance-type: n2-standard-4
    machine.openshift.io/region: europe-southwest1
    machine.openshift.io/zone: europe-southwest1-a
  name: case-03507533-rfctg-master-0-v2
  namespace: openshift-machine-api
spec:
  lifecycleHooks:
    preDrain:
    - name: EtcdQuorumOperator
      owner: clusteroperator/etcd
  metadata: {}
  providerSpec:
    value:
      apiVersion: machine.openshift.io/v1beta1
      canIPForward: false
      credentialsSecret:
        name: gcp-cloud-credentials
      deletionProtection: false
      disks:
      - autoDelete: true
        boot: true
        image: projects/rhcos-cloud/global/images/rhcos-412-86-202303211731-0-gcp-x86-64
        labels: null
        sizeGb: 128
        type: pd-ssd
      kind: GCPMachineProviderSpec
      machineType: n2-standard-8
      metadata:
        creationTimestamp: null
      networkInterfaces:
      - network: case-03507533-rfctg-network
        subnetwork: case-03507533-rfctg-master-subnet
      projectID: cee-gcp-emea
      region: europe-southwest1
      serviceAccounts:
      - email: xxxxxxxxx
        scopes:
        - https://www.googleapis.com/auth/cloud-platform
      tags:
      - case-03507533-rfctg-master
      targetPools:
      - case-03507533-rfctg-api
      userDataSecret:
        name: master-user-data
      zone: europe-southwest1-a


$ oc apply -f new-master0-machine.yaml  machine.machine.openshift.io/case-03507533-rfctg-master-0-v2 created [lperezbe@lperezbe auth]$ oc get machine -n openshift-machine-api NAME                                 PHASE     TYPE            REGION              ZONE                  AGE case-03507533-rfctg-master-0-v2      Running   n2-standard-8   europe-southwest1   europe-southwest1-a   9m39s

cloud compute backend-services describe case-03507533-rfctg-api-internal backends: - balancingMode: CONNECTION   group: https://www.googleapis.com/compute/v1/projects/cee-gcp-emea/zones/europe-southwest1-a/instanceGroups/case-03507533-rfctg-master-europe-southwest1-a - balancingMode: CONNECTION   group: https://www.googleapis.com/compute/v1/projects/cee-gcp-emea/zones/europe-southwest1-b/instanceGroups/case-03507533-rfctg-master-europe-southwest1-b - balancingMode: CONNECTION   group: https://www.googleapis.com/compute/v1/projects/cee-gcp-emea/zones/europe-southwest1-c/instanceGroups/case-03507533-rfctg-master-europe-southwest1-c 

 $ gcloud compute instance-groups list
NAME                                            LOCATION             SCOPE  NETWORK                      MANAGED  INSTANCES
case-03507533-rfctg-master-europe-southwest1-b  europe-southwest1-b  zone   case-03507533-rfctg-network  No       1
case-03507533-rfctg-master-europe-southwest1-a  europe-southwest1-a  zone   case-03507533-rfctg-network  No       0
case-03507533-rfctg-master-europe-southwest1-c  europe-southwest1-c  zone   case-03507533-rfctg-network  No       1

1.
2.
3.

It Could be workarrounded by manually adding the instance into the instance-group

$ gcloud compute instance-groups unmanaged add-instances case-03507533-rfctg-master-europe-southwest1-a --zone=europe-southwest1-a --instances=case-03507533-rfctg-master-0-v2
Updated [https://www.googleapis.com/compute/v1/projects/cee-gcp-emea/zones/europe-southwest1-a/instanceGroups/case-03507533-rfctg-master-europe-southwest1-a]. gcloud compute instance-groups list
NAME                                            LOCATION             SCOPE  NETWORK                      MANAGED  INSTANCES
case-03507533-rfctg-master-europe-southwest1-b  europe-southwest1-b  zone   case-03507533-rfctg-network  No       1
case-03507533-rfctg-master-europe-southwest1-a  europe-southwest1-a  zone   case-03507533-rfctg-network  No       1
case-03507533-rfctg-master-europe-southwest1-c  europe-southwest1-c  zone   case-03507533-rfctg-network  No       1