ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services. All of these kinds of services are used in some form or another by distributed applications.
ZooKeeper aims at distilling the essence of these different services into a very simple interface to a centralized coordination service. The service itself is distributed and highly reliable. Consensus, group management, and presence protocols will be implemented by the service so that the applications do not need to implement them on their own. Application specific uses of these will consist of a mixture of specific components of Zoo Keeper and application specific conventions.
ZooKeeper allows distributed processes to coordinate with each other through a shared hierarchical name space of data registers (we call these registers znodes), much like a file system. Unlike normal file systems ZooKeeper provides its clients with high throughput, low latency, highly available, strictly ordered access to the znodes. The performance aspects of ZooKeeper allow it to be used in large distributed systems. The reliability aspects prevent it from becoming the single point of failure in big systems. Its strict ordering allows sophisticated synchronization primitives to be implemented at the client.
Zookeeper Node Stats
|Zookeeper Server State
|Status of the ZooKeeper. Status is 1 = FOLLOWER, 2 = LEADER, 3 = OBSERVER, 4 = READ_ONLY, 5 = STANDALONE.
|Zookeeper Average Latency (ms)
|Average time in milliseconds for requests to be processed. This is measured since the last restart of the ZooKeeper server.
|Zookeeper Maximum Latency (ms)
|Maximum time in milliseconds for a request to be processed. This is measured since the last restart of the ZooKeeper server.
|Zookeeper Minimum Latency (ms)
|Minimum time in milliseconds for a request to be processed. This is measured since the last restart of the ZooKeeper server.
|Zookeeper Packets Received/Sec
|Number of packets received on the server per second.
|Zookeeper Packets Sent/Sec
|Number of packets sent on the server per second.
|Zookeeper Alive Connections
|Number of active clients connected to a Zookeeper server.
|Zookeeper Outstanding Requests
|Number of currently executing requests on server.
|Zookeeper Node Count
|Number of z-nodes that a ZooKeeper server has in its data tree.
|Zookeeper Watch Count
|Number of watches placed on Z-Nodes on a ZooKeeper server
|Zookeeper Ephemerals Count
|Number of unique ephemeral z-nodes on zookeeper server.
|Zookeeper Open File Descriptor Count
|Number of file descriptors zookeeper server has open.
|Zookeeper Max File Descriptor Count
|Maximum number of file descriptors a zookeeper server can open.
|Zookeeper Approximate Data Size (KB)
|Size in Kilobytes of the data tree for a zookeeper server.
|Number of followers on zookeeper server. This metrics is only for leader, When Zookeeper Server State will be leader (State = 2) then it will be applicable.
|Zookeeper Synced Followers
|Number of followers allow to sync with zookeeper. This metrics is only for leader, When Zookeeper Server State will be leader (State = 2) then it will be applicable.
|Zookeeper Pending Syncs
|Number of pending followers allow to sync with zookeeper. This metrics is only for leader, When Zookeeper Server State will be leader (State = 2) then it will be applicable.