function main(projectId, instance, templateName) {
  // [START compute_template_create_from_instance]
  /**
   * TODO(developer): Uncomment and replace these variables before running the sample.
   */
  // const projectId = 'YOUR_PROJECT_ID';
  // const instance = 'projects/project/zones/zone/instances/instance';
  // const templateName = 'your_template_name';

  const compute = require('@google-cloud/compute');

  // Create a new instance template based on an existing instance.
  // This new template specifies a different boot disk.
  async function createTemplateFromInstance() {
    const instanceTemplatesClient = new compute.InstanceTemplatesClient();

    const [response] = await instanceTemplatesClient.insert({
      project: projectId,
      instanceTemplateResource: {
        name: templateName,
        sourceInstance: instance,
        sourceInstanceParams: {
          diskConfigs: [
            {
              // Device name must match the name of a disk attached to the instance
              // your template is based on.
              deviceName: 'disk-1',
              // Replace the original boot disk image used in your instance with a Rocky Linux image.
              instantiateFrom: 'CUSTOM_IMAGE',
              customImage:
                'projects/rocky-linux-cloud/global/images/family/rocky-linux-8',
              // Override the auto_delete setting.
              autoDelete: true,
            },
          ],
        },
      },
    });
    let operation = response.latestResponse;
    const operationsClient = new compute.GlobalOperationsClient();

    // Wait for the create operation to complete.
    while (operation.status !== 'DONE') {
      [operation] = await operationsClient.wait({
        operation: operation.name,
        project: projectId,
      });
    }

    console.log('Instance template created.');
  }

  createTemplateFromInstance();
  // [END compute_template_create_from_instance]
}
Creates a new instance template based on an existing instance.

@param {string} projectId - Project ID or project number of the Cloud project you use.
@param {string} instance - The instance to base the new template on. This value uses
   the following format: "projects/{project}/zones/{zone}/instances/{instance_name}"
@param {string} templateName - Name of the new template to create.