Persistent disks are implemented as EBS snapshots, so the process is something like:
1. Create EC2 instance for runner #1. Find out there is no existing snapshot, so an empty volume is created and attached.
2. Runner #1 runs exactly 1 job and shuts down. A snapshot is taken for the persistent volume. That's going to be used by later runners.
3. Create EC2 instance for runner #2. Create a new volume based on the last snapshot.
4. Assuming #2 is still running while a new job comes in. Create EC2 instance for runner #3. Create volume based on the same last snapshot.
5. Whenever a runner finishes, its persistent volume gets a snapshot taken. Outdated snapshots are automatically removed.
And yes we manage the AMI that the runner uses. We try out best to follow https://github.com/actions/runner-images and will automate this process very soon so it's always up-to-date.
1. Create EC2 instance for runner #1. Find out there is no existing snapshot, so an empty volume is created and attached.
2. Runner #1 runs exactly 1 job and shuts down. A snapshot is taken for the persistent volume. That's going to be used by later runners.
3. Create EC2 instance for runner #2. Create a new volume based on the last snapshot.
4. Assuming #2 is still running while a new job comes in. Create EC2 instance for runner #3. Create volume based on the same last snapshot.
5. Whenever a runner finishes, its persistent volume gets a snapshot taken. Outdated snapshots are automatically removed.
And yes we manage the AMI that the runner uses. We try out best to follow https://github.com/actions/runner-images and will automate this process very soon so it's always up-to-date.
Edit: formatting