Zero-downtime updates

To keep your service available, you can update instance groups by creating additional instances with new configurations.
As you add VM instances with the new configuration to the group, those with the old configuration will be removed.

For this, follow these steps:

1. Define the instance template you need.
2. Set the deployment policy with a non-zero value for max_expansion, which stands for the maximum number of additional instances to create.
3. Start group updating.

For example, to update a group by adding and removing one VM instance at a time, configure deploy-policy as follows:

...
deploy-policy:
    max_unavailable = 0
    max_expansion = 1
    ...
...

The group will be updated as follows: