Getting Started

Learn ZooKeeper

Curator users are assumed to know ZooKeeper. A good place to start is here: http://zookeeper.apache.org/doc/trunk/zookeeperStarted.html

Using Curator

The Curator JARs are available from Maven Central. The various artifacts are listed here: https://github.com/Netflix/curator/wiki. Users of Maven, Gradle, Ant, etc. can easily include Curator into their build script.

Most users will want to use one of Curator’s pre-built recipes. So, the curator-recipes is the correct artifact to use. If you only want a wrapper around ZooKeeper that adds connection management and retry policies, use curator-framework.

Getting a Connection

Curator uses Fluent Style. If you haven’t used this before, it might seem odd so it’s suggested that you familiarize yourself with the style.

Curator connection instances (CuratorFramework) are allocated from the CuratorFrameworkFactory. You only need one CuratorFramework object for each ZooKeeper cluster you are connecting to:

CuratorFrameworkFactory.newClient(zookeeperConnectionString, retryPolicy)

This will create a connection to a ZooKeeper cluster using default values. The only thing that you need to specify is the retry policy. For most cases, you should use:

RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient(zookeeperConnectionString, retryPolicy);
client.start();

The client must be started (and closed when no longer needed).

Calling ZooKeeper Directly

Once you have a CuratorFramework instance, you can make direct calls to ZooKeeper in a similar way to using the raw ZooKeeper object provided in the ZooKeeper distribution. E.g.:

client.create().forPath("/my/path", myData)

The benefit here is that Curator manages the ZooKeeper connection and will retry operations if there are connection problems.

Recipes

Distributed Lock

InterProcessMutex lock = new InterProcessMutex(client, lockPath);
if ( lock.acquire(maxWait, waitUnit) ) 
{
    try 
    {
        // do some work inside of the critical section here
    }
    finally
    {
        lock.release();
    }
}

Leader Election

LeaderSelectorListener listener = new LeaderSelectorListener()
{
    public void takeLeadership(CuratorFramework client) throws Exception
    {
        // this callback will get called when you are the leader
        // do whatever leader work you need to and only exit
        // this method when you want to relinquish leadership
    }

    public void stateChanged(CuratorFramework client, ConnectionState newState)
    {
        // see https://github.com/Netflix/curator/wiki/Errors
        // You always need to be aware that connections to ZK can fail
    }
}

LeaderSelector selector = new LeaderSelector(client, path, listener);
selector.autoRequeue();  // not required, but this is behavior that you will probably expect
selector.start();

Examples

Examples of Curator usage can be found here: https://github.com/apache/curator/tree/master/curator-examples/src/main/java