ZKUtils (Apache Oozie Core 5.0.0-beta1 API)

java.lang.Object
- org.apache.oozie.util.ZKUtils

```
public class ZKUtils
extends Object
```
This class provides a singleton for interacting with ZooKeeper that other classes can use. It handles connecting to ZooKeeper, service discovery, and publishing metadata about this server.
Users of this class should call register(java.lang.Object) to obtain the singleton. This will ensure that we're properly connected and ready to go with ZooKeeper. When the user is done (i.e. on shutdown), it should call unregister(java.lang.Object) to let this class know; once there are no more users, this class will automatically remove itself from ZooKeeper.
Each Oozie Server provides metadata that can be shared with the other Oozie Servers. To keep things simple and to make it easy to add additional metadata in the future, we share a Map. They keys are defined in ZKUtils.ZKMetadataKeys.
For the service discovery, the structure in ZooKeeper is /oozie.zookeeper.namespace/ZK_BASE_SERVICES_PATH/ (default is /oozie/services/). ZKUtils has a service named "servers" under which each Oozie server creates a ZNode named ${OOZIE_SERVICE_INSTANCE} (default is the hostname) that contains the metadata payload. For example, with the default settings, an Oozie server named "foo" would create a ZNode at /oozie/services/servers/foo where the foo ZNode contains the metadata.
If oozie.zookeeper.secure is set to true, then Oozie will (a) use jaas to connect to ZooKeeper using SASL/Kerberos based on Oozie's existing security configuration parameters (b) use/convert every znode under the namespace (including the namespace itself) to have ACLs such that only Oozie servers have access (i.e. if "service/host@REALM" is the Kerberos principal, then "service" will be used for the ACLs).
Oozie server will shutdown itself if ZK connection is lost for ${ZK_CONNECTION_TIMEOUT}.

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`class`	`ZKUtils.SASLOwnerACLProvider` Simple implementation of an `ACLProvider` that simply returns `saslACL`.
`class`	`ZKUtils.ZKMetadataKeys` Keys used in the metadata provided by each Oozie Server to ZooKeeper and other Oozie Servers

Field Summary

Fields
Modifier and Type	Field and Description
`static String`	`OOZIE_INSTANCE_ID` oozie-env environment variable for specifying the Oozie instance ID
`static String`	`ZK_BASE_SERVICES_PATH` Services that need to put a node in zookeeper should go under here.
`static String`	`ZK_CONNECTION_STRING` oozie-site property for specifying the ZooKeeper connection string.
`static String`	`ZK_CONNECTION_TIMEOUT` Default ZK connection timeout ( in sec).
`static String`	`ZK_MAX_RETRIES` Maximum number of times to retry.
`static String`	`ZK_NAMESPACE` oozie-site property for specifying the ZooKeeper namespace to use (e.g.
`static String`	`ZK_SECURE` oozie-site property for specifying that ZooKeeper is secure.
`static String`	`ZK_SESSION_TIMEOUT` Default ZK session timeout ( in sec).

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`List<org.apache.curator.x.discovery.ServiceInstance<Map>>`	`getAllMetaData()` Returns a list of the metadata provided by all of the Oozie Servers.
`org.apache.curator.framework.CuratorFramework`	`getClient()` Returns the `CuratorFramework` used for managing the ZooKeeper connection; it can be used by calling classes to perform more direct operations on ZooKeeper.
`static org.apache.curator.RetryPolicy`	`getRetryPolicy()` Returns retry policy
`static Set<Object>`	`getUsers()` Useful for tests to get the registered classes
`String`	`getZKId()` Returns the ID of this Oozie Server as seen by ZooKeeper and other Oozie Servers
`int`	`getZKIdIndex(List<org.apache.curator.x.discovery.ServiceInstance<Map>> oozies)` Returns the index of this Oozie Server in ZooKeeper's list of Oozie Servers (ordered by registration time)
`static String`	`getZKNameSpace()` Returns configured zk namesapces
`static ZKUtils`	`register(Object user)` Classes that want to use ZooKeeper should call this method to get the ZKUtils singleton.
`void`	`unregister(Object user)` Classes should call this when they are done (i.e.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - ZK_CONNECTION_STRING
```
public static final String ZK_CONNECTION_STRING
```
    oozie-site property for specifying the ZooKeeper connection string. Comma-separated values of host:port pairs of the ZooKeeper servers.
    
    See Also:
    
    Constant Field Values
  - ZK_NAMESPACE
```
public static final String ZK_NAMESPACE
```
    oozie-site property for specifying the ZooKeeper namespace to use (e.g. "oozie"). All of the Oozie servers that are planning on talking to each other should have the same value for this.
    
    See Also:
    
    Constant Field Values
  - ZK_CONNECTION_TIMEOUT
```
public static final String ZK_CONNECTION_TIMEOUT
```
    Default ZK connection timeout ( in sec).
    
    See Also:
    
    Constant Field Values
  - ZK_SESSION_TIMEOUT
```
public static final String ZK_SESSION_TIMEOUT
```
    Default ZK session timeout ( in sec). If connection is lost after retry, then Oozie server will shutdown itself.
    
    See Also:
    
    Constant Field Values
  - ZK_MAX_RETRIES
```
public static final String ZK_MAX_RETRIES
```
    Maximum number of times to retry.
    
    See Also:
    
    Constant Field Values
  - OOZIE_INSTANCE_ID
```
public static final String OOZIE_INSTANCE_ID
```
    oozie-env environment variable for specifying the Oozie instance ID
    
    See Also:
    
    Constant Field Values
  - ZK_SECURE
```
public static final String ZK_SECURE
```
    oozie-site property for specifying that ZooKeeper is secure.
    
    See Also:
    
    Constant Field Values
  - ZK_BASE_SERVICES_PATH
```
public static final String ZK_BASE_SERVICES_PATH
```
    Services that need to put a node in zookeeper should go under here. Try to keep this area clean and organized.
    
    See Also:
    
    Constant Field Values
- Method Detail
  - register
```
public static ZKUtils register(Object user)
                        throws Exception
```
    Classes that want to use ZooKeeper should call this method to get the ZKUtils singleton.
    
    Parameters:
    
    user - The calling class
    
    Returns:
    
    the ZKUtils singleton
    
    Throws:
    
    Exception - if there is an issue when connecting to ZooKeeper
  - unregister
```
public void unregister(Object user)
```
    Classes should call this when they are done (i.e. shutdown).
    
    Parameters:
    
    user - The calling class
  - getAllMetaData
```
public List<org.apache.curator.x.discovery.ServiceInstance<Map>> getAllMetaData()
```
    Returns a list of the metadata provided by all of the Oozie Servers. Note that the metadata is cached so it may be a second or two stale.
    
    Returns:
    
    a List of the metadata provided by all of the Oozie Servers.
  - getZKId
```
public String getZKId()
```
    Returns the ID of this Oozie Server as seen by ZooKeeper and other Oozie Servers
    
    Returns:
    
    the ID of this Oozie Server
  - getClient
```
public org.apache.curator.framework.CuratorFramework getClient()
```
    Returns the CuratorFramework used for managing the ZooKeeper connection; it can be used by calling classes to perform more direct operations on ZooKeeper. Most of the time, this shouldn't be needed.
    Be careful not to close the connection.
    
    Returns:
    
    the CuratorFramework object
  - getZKIdIndex
```
public int getZKIdIndex(List<org.apache.curator.x.discovery.ServiceInstance<Map>> oozies)
```
    Returns the index of this Oozie Server in ZooKeeper's list of Oozie Servers (ordered by registration time)
    
    Parameters:
    
    oozies - The collection of metadata provided by all of the Oozie Servers (from calling getAllMetaData()
    
    Returns:
    
    the index of this Oozie Server in ZooKeeper's list of Oozie Servers (ordered by registration time)
  - getUsers
```
public static Set<Object> getUsers()
```
    Useful for tests to get the registered classes
    
    Returns:
    
    the set of registered classes
  - getRetryPolicy
```
public static org.apache.curator.RetryPolicy getRetryPolicy()
```
    Returns retry policy
    
    Returns:
    
    RetryPolicy
  - getZKNameSpace
```
public static String getZKNameSpace()
```
    Returns configured zk namesapces
    
    Returns:
    
    oozie.zookeeper.namespace

Class ZKUtils

Nested Class Summary

Field Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

ZK_CONNECTION_STRING

ZK_NAMESPACE

ZK_CONNECTION_TIMEOUT

ZK_SESSION_TIMEOUT

ZK_MAX_RETRIES

OOZIE_INSTANCE_ID

ZK_SECURE

ZK_BASE_SERVICES_PATH

Method Detail

register

unregister

getAllMetaData

getZKId

getClient

getZKIdIndex

getUsers

getRetryPolicy

getZKNameSpace