ZooKeeper ServiceGroup driver

The ZooKeeper ServiceGroup driver works by using ZooKeeper ephemeral nodes. ZooKeeper, in contrast to databases, is a distributed system. Its load is divided among several servers. At a compute worker node, after establishing a ZooKeeper session, the driver creates an ephemeral znode in the group directory. Ephemeral znodes have the same lifespan as the session. If the worker node or the nova-compute daemon crashes, or a network partition is in place between the worker and the ZooKeeper server quorums, the ephemeral znodes are removed automatically. The driver gets the group membership by running the ls command in the group directory.

To use the ZooKeeper driver, you must install ZooKeeper servers and client libraries. Setting up ZooKeeper servers is outside the scope of this guide (for more information, see Apache Zookeeper).

To use ZooKeeper, you must install client-side Python libraries on every nova node: python-zookeeper – the official Zookeeper Python binding and evzookeeper – the library to make the binding work with the eventlet threading model.

The following example assumes the ZooKeeper server addresses and ports are 192.168.2.1:2181, 192.168.2.2:2181, and 192.168.2.3:2181.

The following values in the /etc/nova/nova.conf file (on every node) are required for the ZooKeeper driver:

# Driver for the ServiceGroup serice
servicegroup_driver="zk"

[zookeeper]
address="192.168.2.1:2181,192.168.2.2:2181,192.168.2.3:2181"

To customize the Compute Service groups, use the following configuration option settings: