• State: discussing
• Start date: ?
• End date: ?
• Docs: ?

Release job authors should be able to find out in their drain scripts whether instance is being updated, removed, deleted, etc.

Use cases:

• skip draining data when deployment is deleted
• export data out of cluster when deployment is deleted
• move data to a different node (if it's the only copy) when instance is deleted
• check that data is replicated elsewhere before instance (and its disk) is deleted
• do not move data to a different node when instance is deleted
• deregister etcd member when scaling down instance group
• drain kubelet (talks to master) during update, but not during delete

Drain scripts are called in the following situations:

• During a deployment bosh deploy
  • When updating any job on the instance (includes removing a job)
  • When scaling down an instance
  • When deleting an instance group
  • When removing AZs
  • When the --recreate flag is used
  • When migrating from another instance group [to be investigated]
  • When a VM will become orphaned [to be investigated, see: create-swap-delete]
• During a bosh stop
• During a bosh stop --hard
• During a bosh delete-vm
• During a bosh recreate

The information exposed to the drain script will include:

• The expected (target) state for the instance. We can be in multiple states at the same time (eg. Deleted + Recreated)
  • Deleted (All the above scenarios except bosh stop)
  • Stopped (bosh stop)
  • Recreated (--recreate flag used on deploy, bosh recreate)
• The expected (target) state for the deployment
  • Deleted (bosh delete-deployment)
  • Updated (bosh deploy)
• The expected (target) state for the instance group
  • Scaled-down
  • Removed-AZ
  • Updated

Following environment variables should be passed into bin/drain script with modifications.

BOSH_JOB_STATE={persistent_disk: ...}
BOSH_JOB_NEXT_STATE={persistent_disk: ...}

possible job states: running, stopped, deleted

possible disk states: available, unavailable, deleted

• TBD: job vs instance?
• TBD: colocation of helper jobs: data-exporter?

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