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 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 .
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 .
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.
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 ”.
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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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