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Advanced Level Interview Questions |
Apache ZooKeeper is a distributed, open-source coordination service for distributed applications. It is also called as 'King of Coordination'. It exposes a simple set of primitives that distributed applications can build upon to implement higher level services for synchronization, configuration maintenance, and groups and naming. It is designed to be easy to program to, and uses a data model styled after the familiar directory tree structure of file systems. It runs in Java and has bindings for both Java and C.
Coordination services are notoriously hard to get right. They are especially prone to errors such as race conditions and deadlock. The motivation behind ZooKeeper is to relieve distributed applications the responsibility of implementing coordination services from scratch.
Below are some of the important ZooKeeper interview questions:
Apache ZooKeeper is a highly available service for maintaining small amounts of coordination data, notifying clients of changes in that data, and monitoring clients for failures ZooKeeper is a distributed co-ordination service to manage large set of hosts. Co-ordinating 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.
A distributed application is software that is executed or run on multiple computers within a network and can be stored on servers or with cloud computing. These applications interact in order to achieve a specific goal or task. Traditional applications relied on a single system to run them. Unlike traditional applications that run on a single system, distributed applications run on multiple systems simultaneously for a single task or job.
ZooKeeper is itself a distributed application providing services for developing a distributed application. It coordinates a group of nodes within the cluster and maintains shared data with effective synchronization techniques. Some of the services provided by zookeeper are:
leader and follower
quorumpeermain
In the good old past, each application software was a single program running on a single computer with a single CPU. Today, things have changed. In the Big Data world, application softwares are made up of many independent programs running on an ever-changing set of computers. These applications are known as Distributed Application. A distributed application can run on multiple systems in a network simultaneously by coordinating among themselves to complete a particular task in a fast and efficient manner.
Building distributed systems is hard. Nowadays, a lot of the software applications people use daily, however, depend on such systems, and it doesn’t look like we will stop relying on distributed computer systems any time soon. Coordinating the actions of the independent programs in a distributed systems is far more difficult than writing a single program to run on a single computer. It is easy for developers to get mired in coordination logic and lack the time to write their application logic properly or perhaps the converse, to spend little time with the coordination logic and simply to write a quick-and-dirty master coordinator that is fragile and becomes an unreliable single point of failure.
ZooKeeper was designed to be a robust service that enables application developers to focus mainly on their application logic rather than coordination. It exposes a simple API, inspired by the filesystem API, that allows developers to implement common coordination tasks, such as electing a master server, managing group membership, and managing metadata. ZooKeeper is an application library with two principal implementations of the APIs—Java and C—and a service component implemented in Java that runs on an ensemble of dedicated servers.
When designing an application with ZooKeeper, one ideally separates application data from control or coordination data.
ZooKeeper is a high-performance coordination service for distributed applications. It exposes common services - such as naming, configuration management, synchronization, and group services - in a simple interface so you don't have to write them from scratch. You can use it off-the-shelf to implement consensus, group management, leader election, and presence protocols. And you can build on it for your own, specific needs.
Accessing a znode every time a client needs to know its content would be very expensive. ZooKeeper has an event system referred to as watch which can be set on Znode to trigger an event whenever it is removed, altered or any new children are created below it. Clients register with ZooKeeper to receive notifications of changes to znodes by setting a watch.
znodes are ZooKeeper data nodes. ZooKeeper has a file system-like data model composed of znodes.
Types of znodes: ephemeral, persistent and sequential.
For example, let’s say client created a cznode. In the ZooKeeper server, the cznode will be named like this:
cznode0000000001
If client creates another sequential znode, it would bear the next number in a sequence. So the next sequential znode will be called <znode-name>0000000002.
Sequential znodes play an important role in Locking and Synchronization.
