GAE shutdown or restart all the active instances of a service/app

Question

In my app (Google App Engine Standard Python 2.7) I have some flags in global variables that are initialized (read values from memcache/Datastore) when the instance start (a

Answer 1

It's possible to use the Google Cloud API to stop all the instances. They would then be automatically scaled back up to the required level. My first attempt at this would be a process where:

1. The config item was changed
2. The current list of instances was enumerated from the API
3. The instances were shutdown over a time period that allows new instances to be spun up and replace them, and how time sensitive the config change is. Perhaps close on instance per 60s.

In terms of using the API you can use the gcloud tool (https://cloud.google.com/sdk/gcloud/reference/app/instances/):

gcloud app instances list

Then delete the instances with: gcloud app instances delete instanceid --service=s1 --version=v1

There is also a REST API (https://cloud.google.com/appengine/docs/admin-api/reference/rest/v1/apps.services.versions.instances/list):

GET https://appengine.googleapis.com/v1/{parent=apps/*/services/*/versions/*}/instances
DELETE https://appengine.googleapis.com/v1/{name=apps/*/services/*/versions/*/instances/*}

Answer 2

One possible solution (actually more of a workaround), inspired by your comment on the related post, is to obtain a restart of all instances by re-deployment of the same version of the app code.

Automated deployments are also possible using the Google App Engine Admin API, see Deploying Your Apps with the Admin API:

To deploy a version of your app with the Admin API:

1. Upload your app's resources to Google Cloud Storage.
2. Create a configuration file that defines your deployment.
3. Create and send the HTTP request for deploying your app.

It should be noted that (re)deploying an app version which handles 100% of the traffic can cause errors and traffic loss due to:

• overwriting the app files actually being in use (see note in Deploying an app)
• not giving GAE enough time to spin up sufficient instances fast enough to handle high income traffic rates (more details here)

Using different app versions for the deployments and gradually migrating traffic to the newly deployed apps can completely eliminate such loss. This might not be relevant in your particular case, since the old app version is already impaired.

Automating traffic migration is also possible, see Migrating and Splitting Traffic with the Admin API.