Replace instances in a GCE Managed Instance Group when Templates are updated

gce_igreplace.py

#!/usr/bin/env python
import sys
import time

from googleapiclient import discovery
from oauth2client.client import GoogleCredentials

def get_google_auth(service, version='v2'):
    credentials = GoogleCredentials.get_application_default()
    service_conn = discovery.build(service, version, credentials=credentials)
    return service_conn

def get_instances_in_ig(conn, project, ig):
    zone = ig.get('zone').split('/')[-1]
    for i in conn.instanceGroups().listInstances(instanceGroup=ig.get('name'), project=project, zone=zone, body="").execute().get('items'):
        yield i['instance']

def main(project, ig_prefix):
    compute_conn = get_google_auth('compute', 'v1')
    ig_updater_conn = get_google_auth('replicapoolupdater', 'v1beta1')

    all_instance_groups = compute_conn.instanceGroupManagers().aggregatedList(project=project).execute()
    for location, igms in all_instance_groups.get('items', {}).items():
        for igm in igms.get('instanceGroupManagers', []):
            if igm.get('name', "").startswith(ig_prefix):
                _zone = igm['zone'].split('/')[-1]
                managed_instances = compute_conn.instanceGroupManagers().listManagedInstances(
                        project=project,
                        zone=_zone,
                        instanceGroupManager=igm['name']).execute()
                for i in managed_instances.get('managedInstances', []):
                    _instance_name = i.get('instance', "").split('/')[-1]
                    _instance = compute_conn.instances().get(project=project, zone=_zone, instance=_instance_name).execute()
                    for metadata in _instance['metadata']['items']:
                        if metadata.get('key') == 'instance-template':
                            _instance_template_url = metadata.get('value', "")
                    if igm['instanceTemplate'].split('/')[-1] != _instance_template_url.split('/')[-1]:
                        # Current instance template doesn't match IGM. Start rolling update.
                        _body = {
                            'actionType': 'RECREATE',
                            'instanceTemplate': igm['instanceTemplate'],
                            'instanceGroupManager': igm['selfLink']
                        }
                        print('Updating instance {} with template {}'.format(_instance['name'], igm['instanceTemplate']))
                        print(ig_updater_conn.rollingUpdates().insert(project=project, zone=_zone, body=_body).execute())
                        time.sleep(60)


if __name__ == "__main__":
    if len(sys.argv) != 3:
        print('Must supply a project & a managed instance-group prefix to update')
        sys.exit(1)
    project = sys.argv[1]
    group_prefix = sys.argv[2]
    main(project, group_prefix)