To enable automatic restart for a Compute Engine instance after a maintenance event or failure in GCP, you need to configure the instance’s “On host maintenance” setting to “Automatically restart.” Here are the steps for each method:

1. Using GCP Console:

a. Go to the GCP Console: https://console.cloud.google.com/

b. Navigate to Compute Engine > VM instances.

c. Click on the name of the instance you want to modify.

d. Click the “Edit” button at the top of the page.

e. Under “Availability policies,” set the “On host maintenance” dropdown to “Automatically restart.”

f. Click the “Save” button at the bottom of the page.

2. Using gcloud CLI:

a. Install the Google Cloud SDK and configure authentication: https://cloud.google.com/sdk/docs/install

b. Update the instance’s “On host maintenance” setting using the gcloud compute instances update command:

gcloud compute instances update INSTANCE_NAME --zone ZONE --maintenance-policy MIGRATE

Replace INSTANCE_NAME and ZONE with appropriate values. The --maintenance-policy MIGRATE flag sets the “On host maintenance” setting to “Automatically restart.”

3. Using Terraform:

a. Update the main.tf file to enable automatic restart for the instance:

resource "google_compute_instance" "example" {
  name         = "example-instance"
  machine_type = "n1-standard-1"
  zone         = "us-central1-a"

  # ... other settings ...

  scheduling {
    on_host_maintenance = "MIGRATE"
  }
}

The on_host_maintenance = "MIGRATE" line sets the “On host maintenance” setting to “Automatically restart.”

b. Run the following commands to apply the changes:

terraform init
terraform plan
terraform apply

By following these steps, you can enable automatic restart for a Compute Engine instance after a maintenance event or failure in GCP using the GCP Console, gcloud CLI, or Terraform. Automatic restart helps to maintain the availability of your instance, but keep in mind that it may not protect against all types of failures or issues, so it’s essential to have a robust backup and recovery strategy in place.