What is Apache Zookeeper?

What is Apache Zookeeper?

It is a software project of Apache Software Foundation. It is an open-source technology. This will maintain configuration information. Also, it will provide synchronized as well as the group services. It will deploy on Hadoop cluster to administer the infrastructure.

Why Do We Need Apache Zookeeper?

Before we go in-depth about ZooKeeper. First, we understand how the Apache ZooKeeper came into existence.

The ZooKeeper is a framework. It has originally built by Yahoo. This is for easier accessing of the apps. But, later, ZooKeeper will use for industrial services. They will use this by the distributed frameworks like Hadoop, HBase, etc. That’s why the Apache ZooKeeper became a standard. It will design to be a vigorous service. This will enable the app developers to focus mainly on their app logic. This is rather than the coordination.

This is a difficult process to coordinate and managing the service. This is especially in the distributed environment. Especially, the Apache ZooKeeper is used to solve this kind of problem. This is possible with the help of its simple architecture and its API. This will allow the developers to implement common coordination tasks. Following are some of the common coordination tasks. They are,

  • Electing the master server.
  • Managing the group membership.
  • Managing the metadata.

The Apache ZooKeeper is used to maintain the following. They are,

  • Centralized configuration information.
  • Naming.
  • Providing the distributed synchronization.
  • Providing the group services. 

This will be in a simple interface. So that, we don’t have to write it from the scratch. The Apache Kafka also uses the ZooKeeper. This is to manage the configuration. ZooKeeper will allow the developers to focus on the core app logic. Also, it will implement the various protocols. This will be especially on the cluster. So that, these apps will not need to implement by themselves.

ZooKeeper Architecture:

Apache ZooKeeper works on the Client–Server architecture. This is the clients are machine nodes. The servers are nodes.

The following figure shows the relationship between the servers and their clients. In this, we can see that each client sources the client library. Also, further they communicate with any of the ZooKeeper nodes.

Following table will explain the components of this architecture. Let us see in detail.

S: No





Client node in our distributed apps cluster. It is used to access information from the server. It will send a message to the server. This is to let the server know that the client is alive. Also, if there is no response from the connected server. Then the client will automatically resend the message to another server.



The server gives an acknowledgement. This is to the client to inform that the server is alive. Also, it will provide all services to the clients.



If any of the server nodes will fail? Then, this server node will perform the automatic recovery.



It is a server node which follows the instructions given by the leader.

Working of the Apache ZooKeeper:

Following are some of the working of the Apache Zookeeper. They are,

  • The first thing that happens as soon as the ensemble starts is, it waits for the clients. It is to connect to the servers.
  • After that, the clients in the ZooKeeper ensemble. It will connect to one of the nodes. That node can be any of a leader node or a follower node.
  • Once the client is connected to a node. The node will assign a session ID to the client. Then it will send an acknowledgement to that client.
  • If the client does not get any acknowledgement from the node. Then it will resend the message to another node in the ZooKeeper ensemble. Also, it will try to connect with it.
  • On receiving the acknowledgement, the client makes sure that the connection. Either it connection will not lose. This is by sending the heartbeats to the node at regular intervals.
  • Finally, the client can perform functions like read and write. It can also store the data as per the needs.

Features of the Apache ZooKeeper:

Apache ZooKeeper will provide a wide range of good features to the user. Let us start exploring them. They are,

  • Updating the Node’s Status: 

Apache ZooKeeper is capable of updating every node. That will allow it to store updated information about each node. This will be across the cluster.

  • Managing the Cluster: 

This technology can manage the cluster. This will be in such a way that the status of each node will maintain in real time. Also, leaving lesser chances for errors as well as ambiguity.

  • Naming Service: 

ZooKeeper will attache a unique identification. This is to every node. It is quite similar to the DNA that will help to identify it.

  • Automatic Failure Recovery: 

Apache ZooKeeper will lock the data while modifying. This will help the cluster. This is to recover it automatically if a failure occurs in the database.

Benefits of the Apache ZooKeeper:

Now we have understood what Apache ZooKeeper is. Let us now discuss about its benefits. Here are some of the advantages of working with Apache ZooKeeper. They are as follows.

  • Simplicity: 

Coordination is possible with the help of a shared hierarchical namespace.

  • Reliability:

The system will keep performing even if more than one node fails.

  • Order: 

It will keep tracking simply by stamping each update. This is possible with a number denoting its order.

  • Speed: 

It will run with a ratio of 10:1 in the cases where ‘reads’ are more common.

  • Scalability: 

The performance can enhance by deploying more machines.

ZooKeeper Use Cases:

There are many use cases of ZooKeeper. Some of the most prominent of them are as follows. They are,

  • Managing the configuration.
  • Naming the services.
  • Choosing the leader.
  • Queuing the messages.
  • Managing the notification system.
  • Synchronization.

One of the ways in which we can communicate with the ZooKeeper ensemble is by using the ZooKeeper CLI. This will give us the feature of using various options. Also, for the sake of debugging. There will increase dependence on the CLI.

I hope now you understand the concept of Apache Zookeeper. Also, the working, features as well as its benefits. Here we also see some use case of  the Apache Zookeeper.

October 18, 2019
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