{"id":79568,"date":"2020-08-20T15:24:54","date_gmt":"2020-08-20T09:54:54","guid":{"rendered":"https:\/\/techvidvan.com\/tutorials\/?p=79568"},"modified":"2020-08-20T15:24:54","modified_gmt":"2020-08-20T09:54:54","slug":"apache-zookeeper-tutorial","status":"publish","type":"post","link":"https:\/\/techvidvan.com\/tutorials\/apache-zookeeper-tutorial\/","title":{"rendered":"Apache Zookeeper Tutorial for Beginners"},"content":{"rendered":"

If you are eager to learn about Apache Zookeeper without referring to any book, then it is the right article for you. In this ZooKeeper tutorial article, you will explore what Apache ZooKeeper is and why we use Apache Zookeeper. The article will explain every concept related to Apache Zookeeper.<\/p>\n

Let’s start our new journey towards ZooKeeper. This tutorial article will give you the reason for why you should learn ZooKeeper and also enlist the companies using ZooKeeper.<\/p>\n

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Introduction to Apache Zookeeper<\/h3>\n

Apache ZooKeeper is basically a distributed coordination service for managing a large set of hosts. Coordinating and managing the service in the distributed environment is really a very complicated process.<\/p>\n

Apache ZooKeeper, with its simple architecture and API, solves this issue. ZooKeeper allows the developer to focus on the core application logic without being worried about the distributed nature of the application.<\/p>\n

Originally, Yahoo built the ZooKeeper framework in order to access their applications in an easy and robust manner. Later on, Apache ZooKeeper became the standard for the organized service used by Apache Hadoop, HBase, and various other distributed frameworks.<\/p>\n

For example, HBase uses Apache ZooKeeper for tracking the status of the distributed data.<\/p>\n

In simple words, Zookeeper is one of the top-notch cluster coordination services that use the most robust synchronization techniques for keeping the nodes perfectly connected in the cluster.<\/p>\n

Apache Zookeeper, with its simple architecture and API, solves the management of the distributed environment.<\/p>\n

Distributed Application<\/h3>\n

A distributed application is the application that can run on the multiple systems in a network simultaneously by coordinating among themselves in order to complete the specific task in an efficient manner.<\/p>\n

The distributed application can complete the complex and the time-consuming tasks in minutes as compared to the non-distributed application that will take hours to complete the task.<\/p>\n

The distributed application uses the computing capabilities of all the machines involved. We can further reduce the time to complete the task by configuring the distributed application to run on more nodes in the cluster.<\/p>\n

A distributed application consists of two parts, that is, Server and Client application. The server applications are actually distributed and they have a common interface so that the clients can connect to any server in a cluster and get the same result.<\/p>\n

The client applications were the tools for interacting with the distributed application.<\/p>\n

Benefits of Distributed Applications<\/h3>\n

The distributed applications offer various benefits such as:<\/p>\n

1. Reliability \u2212<\/strong> If the single node or the few systems fails, then it doesn\u2019t make the whole system fail.<\/p>\n

2. Scalability \u2212<\/strong> We can easily increase the performance when needed by adding more machines with the minor changes in the application configuration without any downtime.<\/p>\n

3. Transparency \u2212<\/strong> It hides the complexity of the entire system and depicts itself as a single entity or application.<\/p>\n

Challenges of Distributed Applications<\/h3>\n

1. Partial failure<\/h4>\n

It is one of the major challenges in distributed applications.<\/p>\n

For example<\/strong>, Suppose that there are two nodes, that is, Node 1 and Node 2, in the distributed system. Node 1 sends a message to Node 2 over the network. However, if the network fails before Node 1 receives an acknowledgment from the Node 2, then Node 1 doesn\u2019t know whether the Node 2 has got the message or not.<\/p>\n

Node 1 will know the actual status only when the network gets connected again. This situation is known as a partial failure in distributed applications.<\/p>\n

Apache Zookeeper provides a mechanism to handle partial failure efficiently.<\/p>\n

2. Race Conditions<\/h4>\n

A race condition will take place in the distributed applications when the multiple machines are waiting for the same resource to get free.
\nFor example<\/strong>, suppose that there are four different nodes in the distributed system and only Node1 is using the resource.<\/p>\n

So, in such a case, Node 1 has an exclusive lock on the resource. Also, let assume that at the same time, all the other three nodes are waiting for the resource to become free.<\/p>\n

So, when Node 1 releases the resource, then the remaining nodes will race to acquire the resource. Out of these 3 only one of them will succeed while the others will go back to the waiting state.<\/p>\n

The above process will continue until all the nodes in the system get the resource. This condition is called a race condition.<\/p>\n

3. Deadlocks in Apache Zookeeper<\/h4>\n

Deadlocks occur in the situation when there is a cyclic dependency on the resources.<\/p>\n

For example<\/strong>, there are two machines, named Machine 1 and Machine 2, and two resources, named resource A and resource B. If the machine 1 has locked resource A and is eagerly waiting to lock the resource B.<\/p>\n

And at the same time, the machine 2 has locked the resource B and is waiting to lock the resource A. In this situation, none of the locks can be acquired or released. This leads to the deadlock condition.<\/p>\n

In order to resolve this deadlock, either of the processes has to be killed and we have to redo the processing.
\nDeadlock detection is CPU-intensive and is an expensive operation.<\/p>\n

4. Inconsistencies<\/h4>\n

Inconsistencies will take place in the situation when the changes are not propagated to all the nodes\/machines in the distributed system.<\/p>\n

Why we use Zookeeper?<\/h3>\n

ZooKeeper framework provides the complete mechanism for overcoming all the challenges faced by the distributed applications. Apache Zookeeper handles the race condition and the deadlock by using the fail-safe synchronization approach. It also handles the inconsistency of data by atomicity.<\/p>\n

Apache ZooKeeper is basically a service that is used by the cluster to coordinate between themselves and maintain the shared data with the robust synchronization techniques.
\nApache ZooKeeper is itself a distributed application providing services for writing the distributed application.<\/p>\n

The various services provided by Apache ZooKeeper are as follows \u2212<\/p>\n