What is Apache Zookeeper and How Does It Work?

What is a Distributed System?

A distributed application is an application that can run on multiple systems in a network. It runs simultaneously by coordinating itself to complete a certain task. These tasks may take plenty of hours to complete by any non-distributed application.

Introduction to Apache Zookeeper

ZooKeeper is an open-source Apache project that provides a centralized service for providing configuration information, naming, synchronization and group services over large clusters in distributed systems. 

The goal is to make these systems easier to manage with improved, more reliable propagation of changes.

ZooKeeper is a distributed coordination service to manage a large set of hosts. Coordinating and managing a service in a distributed environment is a complicated process. ZooKeeper solves this issue with its simple architecture and API. ZooKeeper allows developers to focus on core application logic without worrying about the distributed nature of the application.

It is also worth noting that the ZooKeeper framework was originally built at Yahoo for accessing their applications in an easy and robust manner. Later, Apache ZooKeeper became a standard for organized service used by Hadoop, HBase, and other distributed frameworks.

How Does Apache Zookeeper Work?

Apache ZooKeeper is simple 

ZooKeeper allows distributed processes to coordinate with each other through a shared hierarchical namespace organized similarly to a standard file system. The namespace consists of data registers – called znodes, in ZooKeeper parlance – and these are similar to files and directories.

Unlike a typical file system designed for storage, ZooKeeper data is kept in memory, which means ZooKeeper can achieve high throughput and low latency numbers.

Apache ZooKeeper is replicated 

Like the distributed processes it coordinates, ZooKeeper itself is intended to be replicated over a set of hosts called an ensemble.

Let us digest what the image above describes. The servers that make up the ZooKeeper service must all know about each other. They maintain an in-memory image of the state, along with a transaction logs and snapshots in a persistent store. As long as a majority of the servers are available, the ZooKeeper service will be available.

Clients connect to a single ZooKeeper server. The client maintains a connection through which it sends and gets responses. If the TCP connection to the server breaks, the client will connect to a different server.

Advantages of Apache Zookeeper

Now that we have known how does Apache Zookeeper works, let us discuss the advantages of it.

  • Apache Zookeeper is a simple distributed coordination process
  • Mutual exclusion and co-operation between server processes
  • Apache Zookeeper handles ordered messages
  • Encode the data according to specific rules. Ensure your application runs consistently. This approach can be used in MapReduce to coordinate queue to execute running threads.
  • Data transfer either succeed or fail, but no transaction is partial.

What can Apache Zookeeper be used for?

Apache ZooKeeper is a service used by a cluster to coordinate between themselves and maintain shared data with robust synchronization techniques. Zookeeper can provide services as below:

  • Naming service − Identifying the nodes in a cluster by name. It is similar to DNS but for nodes.
  • Configuration management − Latest and up-to-date configuration information of the system for a joining node.
  • Cluster management − Joining/leaving a node in a cluster and node status in real-time.
  • Leader election − Electing a node as a leader for coordination purpose.
  • Locking and synchronization service − Locking the data while modifying it.
  • Highly reliable data registry − Availability of data even when one or a few nodes are down.

Apache Zookeeper can also be used in Hadoop. Apache Hadoop is the driving force behind the growth of the Big Data industry. Hadoop relies on ZooKeeper for configuration management and coordination. Multiple ZooKeeper servers can be used to support large Hadoop clusters. Each client machine communicates with one of the ZooKeeper servers to retrieve and update its synchronization information.

Summary – Why Should We Use Zookeeper?

The Big Data world is a dynamic place offering numerous jobs to people belonging to diverse educational and professional background. Apache ZooKeeper is a distributed coordination service to manage a large set of hosts. Coordinating and managing a service in a distributed environment is a complicated process. Apache ZooKeeper solves this issue with its simple architecture and API.

Apache ZooKeeper would be best suited to the candidates aspiring to become software professionals, administrators, Big Data professionals, etc. It is suitable for both beginners and experience holders in this area.

However, having a basic knowledge of distributed systems, high-level programming is recommended to understand ZooKeeper concepts in a rather better fashion.