---
prelude: |
  This is expected to be the last 3.x release of Zuul (barring any
  unanticipated bugfix releases).

  The next release of Zuul, 4.0.0, will require the following
  deployment changes:

    * TLS ZooKeeper connections
    * Network connectivity from all components to ZooKeeper
    * A SQL database

  These features are supported now, so it is important that you take
  this time to :ref:`switch your ZooKeeper connection to use
  TLS<zk-encrypted-connections>`, and :ref:`configure a SQL
  connection<sql-driver>`.  Even though only some Zuul components
  connect to ZooKeeper today, you should ensure that the
  ``[zookeeper]`` section is present in ``zuul.conf`` for all
  components, and that they have network connectivity to the ZooKeeper
  servers.  Doing so will make the upgrade to 4.0.0 seamless.

  These changes are in support of ongoing work to enable multiple
  scheduler processes for scaling and availability.  After the 4.0.0
  release, it is anticipated that further upgrades to Zuul made in
  support of this work will be done with minimal disruption in the
  course of normal releases.