How to change an external ephemeral ip

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I have a VM instance in Google Cloud with external ephemeral IP. The IP is supposed to change when the instance is stopped and started but it does not. How can I manually change the ephemeral IP?

google-compute-engine google-cloud-platform ip
1 Answers

Accordingly to the documentation IP Addresses section External IP addresses:

Ephemeral external IP addresses are available to VM instances and forwarding rules. Ephemeral external IP addresses remain attached to a VM instance only until the VM is stopped and restarted or the instance is terminated. If an instance is stopped, any ephemeral external IP addresses that are assigned to the instance are released back into the general Compute Engine pool and become available for use by other projects. When a stopped instance is started again, a new ephemeral external IP address is assigned to the instance.

As a possible workaround you can reserve an external IP address each time when you want to change it. Please have a look at my steps below:

  1. create VM instance:
$ gcloud compute instances create instance-1 --zone=us-central1-a --machine-type=n1-standard-1 --image=ubuntu-1804-bionic-v20200610 --image-project=ubuntu-os-cloud
Created [https://www.googleapis.com/compute/v1/projects/test-prj/zones/us-central1-a/instances/instance-1].
NAME        ZONE           MACHINE_TYPE   PREEMPTIBLE  INTERNAL_IP  EXTERNAL_IP   STATUS
instance-1  us-central1-a  n1-standard-1               10.128.0.5   35.239.122.55  RUNNING
  1. reserve an external IP address:
$ gcloud compute addresses create external-ip-upd-1 --region=us-central1
Created [https://www.googleapis.com/compute/v1/projects/test-prj/regions/us-central1/addresses/external-ip-upd-1
$ gcloud compute addresses list
NAME               ADDRESS/RANGE  TYPE      PURPOSE  NETWORK  REGION        SUBNET   STATUS
external-ip-upd-1  34.66.150.26   EXTERNAL                    us-central1            RESERVED
  1. unassign existing external IP of VM instance:
$ gcloud compute instances describe instance-1 --zone=us-central1-a 
...
networkInterfaces:
- accessConfigs:
  - kind: compute#accessConfig
    name: external-nat
    natIP: 34.66.150.26
    networkTier: PREMIUM
    type: ONE_TO_ONE_NAT
  fingerprint: 4vzdAl27owk=
  kind: compute#networkInterface
  name: nic0
  network: https://www.googleapis.com/compute/v1/projects/test-prj/global/networks/default
  networkIP: 10.128.0.5
  subnetwork: https://www.googleapis.com/compute/v1/projects/test-prj/regions/us-central1/subnetworks/default
...
$ gcloud compute instances delete-access-config instance-1 --access-config-name "external-nat" --zone=us-central1-a
Updated [https://www.googleapis.com/compute/v1/projects/test-prj/zones/us-central1-a/instances/instance-1].
$ gcloud compute instances list
NAME                  ZONE            MACHINE_TYPE   PREEMPTIBLE  INTERNAL_IP  EXTERNAL_IP     STATUS
instance-1            us-central1-a   n1-standard-1               10.128.0.5                   RUNNING
  1. assign new external IP:
$ gcloud compute instances add-access-config instance-1 --access-config-name "external-nat-upd-1" --address 34.66.150.26 --zone=us-central1-a
Updated [https://www.googleapis.com/compute/v1/projects/test-prj/zones/us-central1-a/instances/instance-1].
$ gcloud compute instances list
NAME                  ZONE            MACHINE_TYPE   PREEMPTIBLE  INTERNAL_IP  EXTERNAL_IP     STATUS
instance-1            us-central1-a   n1-standard-1               10.128.0.5   34.66.150.26    RUNNING
  1. repeat 2-4 for the next change and release unused external IP:
$ gcloud compute addresses create external-ip-upd-2 --region=us-central1 
$ gcloud compute addresses list
NAME               ADDRESS/RANGE  TYPE      PURPOSE  NETWORK  REGION        SUBNET   STATUS
external-ip-upd-2  34.71.149.223  EXTERNAL                    us-central1            RESERVED
external-ip-upd-1  34.66.150.26   EXTERNAL                    us-central1            IN_USE
$ gcloud compute instances delete-access-config instance-1 --access-config-name "external-nat-upd-1" --zone=us-central1-a
$ gcloud compute instances add-access-config instance-1 --access-config-name "external-nat-upd-2" --address 34.71.149.223 --zone=us-central1-a
$ gcloud compute instances list
NAME                  ZONE            MACHINE_TYPE   PREEMPTIBLE  INTERNAL_IP  EXTERNAL_IP     STATUS
instance-1            us-central1-a   n1-standard-1               10.128.0.5   34.71.149.223   RUNNING
$ gcloud compute addresses delete external-ip-new --region=us-central1

If you noticed that newly reserved IP was used some time ago you can reserve another IP address to get another one and then release unused IPs.

UPDATE If you think that you found an issue you can file a report at Google Public Issue Tracker or request a feature to avoid manual reconfiguration.

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