Before going to know about Zookeeper, let us know about Distributed applications.

Distributed applications are the applications or software that  run on a multiple computers  within a network  which can be stored on servers  or with cloud computing .Unlike traditional applications ,   distributed applications works  on a multiple  system for a single task or job. The distributed nature of work refers to data being spread more than one computer in the network. Distributed applications can communicate with multiple servers or devices on the same network from any geographical location. Due to Clouds elasticity  and scalability as well as the ability to handle large applications , many  developers, IT  professionals  or enterprises choose to store apps in the cloud.

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Zookeeper :

Zookeeper is a centralized service for maintaining configuration information, naming distributed synchronization and providing group services.  All these kinds of services , were used in same form or another by distributed applications . Each time , when they are implemented there is a lot of work which goes into the fixing the bugs .

Terminologies : 

Znode :   The data  in the zookeeper is organized into a hierarchal  name space of data nodes called Znodes . A  Znode can have data associated with it as well as child Znodes . The data in the znode is stored in a binary format , where it can be imported  or exported and can view as a JSON   data. Paths to Znode were usually expressed as slash separated  canonical , absolute  paths.

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Ephemeral nodes :  It is also  a znode  which exists only for the duration of active session.It is deleted when the znode is deleted.  This node cannot have children.

Client : It is a host or process , which uses the Zookeeper service

Server : A Zookeeper consists of  one or more machines , each machine is a server  ehcih runs in its own JVM  and listens to its own set of ports .  You can several zoo keeper servers at once on a single workstation, by configuring the ports for each server  for testing purpose.

 Quorum : it is a set of Zookeeper services.  It must be  an odd number .For most of the  deployments , 3 servers were required .

Work Flow :

Once a Zookeeper ensemble starts ,it waits for the clients to connect . Clients will connect to the one of the nodes in the  Zookeeper ensemble. It can be a leader  or follower .Once a client is connected , the node assigns a Session ID  to that particular client.  If the client does not get any acknowledgement , it simply tries to connect to  the other nodes in the Zookeeper ensemble . Once it gets connected t o a node , client will send heart beats to a node in a regular interval of time to ensure connection is not lost .

 When the client reads  a particular znode, it sends a read request with the znode path where the node returns a  requested znode  by getting  its from its own database.

If the client wants to  store data in the  Zookeeper   ensemble, it sends a znode path and data to the server.  The connected server , will forward a request to the leader , where the leader will reissue the writing  request to all the  followers .  If only the majority of the nodes respond successfully, then write request will succeed  and successful  code is sent to the client . If not , the write request will  fail.

Features :

 Reliable system :  The system is reliable, which keeps running even if the nodefails.

Simple architecture : The architecture is quite simple which helps in coordinating the process because of its shared hierarchical name space.

Scalable : Its performance can be improved by adding the nodes .

Fast processing : It is specially fast in “ read dominant work loads ”.

Recommended Audience :

 Software developers

ETL  developers

Project Managers

Team Lead’s

Business Analyst

Prerequisites :

There is nothing much  prerequisite for learning Big Data Hadoop .Its good to have a knowledge on  some  OOPs Concepts . But it is not mandatory .Our Trainers  will teach you if you don’t have a knowledge on  those OOPs Concepts

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