features:
  - |
    Mistral engine now supports graceful scale-in. That is, if a number of
    engines in a cluster needs to be reduced manually it is now possible to
    do w/o breaking currently running workflows. In order to shutdown a
    Mistral engine, SIGTERM signal needs to be sent to the corresponding
    process. In Unix operatating systems it's a matter of running the command
    "kill <engine PID>" in any shell. When this signal is caught by the
    process, it has a certain amount of time configured by the
    'graceful_shutdown_timeout' property to complete currently running
    database transactions and process all buffered RPC messages that have
    already been polled from the queue. After this time elapses, the process
    will be forced to exit.
    By default, the value of the 'graceful_shutdown_timeout' property is
    60 (seconds).

Add a release note for graceful scale-in feature
Add a release note for graceful scale-in feature

Change-Id: I9874085555db097c7ae1ae3c2c7cad73b8543ff5
