ZooKeeper is a distributed coordination service that provides a simple interface for building distributed applications. The main components of ZooKeeper are:
- Ensemble: A ZooKeeper ensemble is a collection of servers that work together to provide a distributed coordination service. The minimum recommended ensemble size is three servers, but larger ensembles can provide greater availability and fault tolerance.
- Znodes: Znodes are nodes in the ZooKeeper tree data structure. Each znode can contain data and can have child znodes, similar to a filesystem. Znodes are used to store configuration information, status information, and other data needed by distributed applications.
- Watches: Watches are notifications that are sent to clients when changes occur in the ZooKeeper tree. Clients can register watches on znodes, and ZooKeeper will send a notification to the client when the znode changes.
- ACLs: Access Control Lists (ACLs) are used to control access to znodes. Each znode can have an ACL that specifies which clients can read or write to the znode.
- Client APIs: ZooKeeper provides APIs for Java, C, Python, and other programming languages. These APIs allow clients to interact with the ZooKeeper ensemble and perform operations such as creating znodes, reading and writing data, and registering watches.
- Leader Election: ZooKeeper provides a built-in mechanism for leader election, which can be used to elect a leader from a group of servers. This is useful in distributed systems where only one server should be responsible for a particular task at any given time.
- Atomic Broadcast: ZooKeeper provides an atomic broadcast protocol that can be used to ensure that messages are delivered to all members of a group in the same order. This is useful for implementing distributed systems where consistency is important.
- Sessions: When a client connects to a ZooKeeper ensemble, it creates a session. Sessions are used to track the client’s state and maintain its connection to the ensemble. Clients can set a timeout for their session, after which the session will be closed if the client does not send any requests.
- Quorum: In a ZooKeeper ensemble, a quorum is a majority of the servers. A quorum must be present and reachable for the ensemble to function correctly. For example, if an ensemble has five servers, a quorum would consist of at least three servers.
- Transactions: ZooKeeper provides support for transactions, which allow multiple operations to be grouped together and executed as a single atomic operation. This is useful for maintaining consistency in distributed systems.
- Watches Triggers: Watches can be set to trigger certain actions when an event occurs. For example, a watch could be set to trigger a notification to a client when a znode is deleted or when new data is written to a znode.
- Time Service: ZooKeeper provides a time service that can be used to synchronize clocks across different nodes in a distributed system. This is useful for ensuring that different nodes are operating on a consistent timeline.
These are just a few more components of ZooKeeper (Java Management Extensions (JMX), Watcher Service, Snapshot and Log, Four Letter Words (4lw), Dynamic Reconfiguration, ZooKeeper Atomic Broadcast protocol ZAB etc). that demonstrate its robustness and versatility in distributed systems.
Let me know if you need more explaination of above bullet components. I have best knowledge of deploying zookeeper with kafka.
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