Interview Questions.

Question 1. What Is Zookeper?

Answer :

ZooKeeper is a dispensed co-ordination provider to manage massive set of hosts. Co-ordinating and dealing with a service in a allotted surroundings is a complicated manner. ZooKeeper solves this issue with its simple architecture and API. ZooKeeper lets in builders to focus on core application logic with out demanding about the distributed nature of the application.

The ZooKeeper framework changed into at first constructed at “Yahoo!” for accessing their packages in an clean and sturdy way. Later, Apache ZooKeeper became a preferred for organized carrier utilized by Hadoop, HBase, and other allotted frameworks.

Question 2. What Are The Benefits Of Distributed Applications?

Answer :

Reliability:Failure of a unmarried or some systems does no longer make the whole device to fail.

Scalability : Performance may be improved as and while needed with the aid of including extra machines with minor alternate in the configuration of the software without a downtime.

Transparency: Hides the complexity of the device and suggests itself as a single entity / application.

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Question 3. What Are The Challenges Of Distributed Applications?

Answer :

Race condition: Two or more machines seeking to perform a particular assignment, which really desires to be executed simplest by a unmarried machine at any given time. For instance, shared resources ought to simplest be changed by means of a unmarried gadget at any given time.

Deadlock:Two or extra operations looking forward to each other to complete indefinitely.

Inconsistency:Partial failure of records.

Question four. What Is Apache Zookeeper Meant For?

Answer :

Apache ZooKeeper is a carrier utilized by a cluster (institution of nodes) to coordinate between themselves and maintain shared statistics with strong synchronization techniques. ZooKeeper is itself a distributed application offering services for writing a dispensed software.

The common offerings provided with the aid of ZooKeeper are as follows :

Naming service:Identifying the nodes in a cluster by using call. It is just like DNS, however for nodes.

Configuration control: Latest and up to date configuration facts of the machine for a joining node.

Cluster management:Joining / leaving of a node in a cluster and node reputation at actual time.

Leader election:Electing a node as chief for coordination motive.

Locking and synchronization provider:Locking the records while editing it. This mechanism allows you in automatic fail restoration while connecting other disbursed programs like Apache HBase.

Highly reliable facts registry:Availability of information even if one or some nodes are down.

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Question 5. What Are The Benefits Of Zookeeper?

Answer :

Here are the advantages of the usage of ZooKeeper:

Simple allotted coordination process
Synchronization:Mutual exclusion and co-operation among server processes. This procedure enables in Apache HBase for configuration control.
Ordered Messages
Serialization :Encode the statistics in line with particular guidelines. Ensure your utility runs constantly. This technique may be used in MapReduce to coordinate queue to execute jogging threads.
Reliability
Atomicity:Data switch both be triumphant or fail completely, however no transaction is partial.
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Question 6. Explain The Types Of Znodes?

Answer :

Znodes are categorized as endurance, sequential, and ephemeral.

Persistence znode - Persistence znode is alive even after the patron, which created that precise znode, is disconnected. By default, all znodes are chronic until otherwise targeted.

Ephemeral znode - Ephemeral znodes are lively until the customer is alive. When a customer gets disconnected from the ZooKeeper ensemble, then the ephemeral znodes get deleted routinely. For this purpose, best ephemeral znodes aren't allowed to have a children further. If an ephemeral znode is deleted, then the following suitable node will fill its position. Ephemeral znodes play an important position in Leader election.

Sequential znode - Sequential znodes can be both chronic or ephemeral. When a new znode is created as a sequential znode, then ZooKeeper sets the direction of the znode by attaching a 10 digit collection number to the unique name. For example, if a znode with course /myapp is created as a sequential znode, ZooKeeper will trade the course to /myapp0000000001 and set the subsequent series range as 0000000002. If  sequential znodes are created simultaneously, then ZooKeeper by no means makes use of the equal variety for every znode. Sequential znodes play an important role in Locking and Synchronization.

Question 7. Explain The Zookeeper Workflow?

Answer :

Once a ZooKeeper ensemble starts, it's going to watch for the customers to connect. Clients will connect with one of the nodes in the ZooKeeper ensemble. It may be a leader or a follower node. Once a consumer is attached, the node assigns a consultation ID to the precise customer and sends an acknowledgement to the client. If the consumer does now not get an acknowledgment, it genuinely tries to connect some other node within the ZooKeeper ensemble. Once related to a node, the consumer will ship heartbeats to the node in a everyday c language to make certain that the relationship is not lost.

If a consumer wants to read a specific znode, it sends a examine request to the node with the znode path and the node returns the requested znode through getting it from its own database. For this reason, reads are rapid in ZooKeeper ensemble.

If a patron desires to save information within the ZooKeeper ensemble, it sends the znode course and the records to the server. The related server will ahead the request to the chief and then the chief will reissue the writing request to all the fans. If simplest a majority of the nodes reply efficaciously, then the write request will prevail and a a hit go back code might be despatched to the customer. Otherwise, the write request will fail. The strict majority of nodes is referred to as as Quorum.

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Question 8. Explain The Cli In Zookeeper?

Answer :

ZooKeeper Command Line Interface (CLI) is used to have interaction with the ZooKeeper ensemble for improvement motive. It is useful for debugging and working around with extraordinary alternatives. To carry out ZooKeeper CLI operations, first activate your ZooKeeper server (“bin/zkServer.Sh begin”) after which, ZooKeeper purchaser (“bin/zkCli.Sh”).

Once the customer begins, you can perform the subsequent operation:

Create znodes
Get information
Watch znode for adjustments
Set records
Create youngsters of a znode
List children of a znode
Check Status
Remove / Delete a znode
Question 9. How Can We Create Znodes?

Answer :

Create a znode with the given path. The flag argument specifies whether or not the created znode can be ephemeral, persistent, or sequential. By default, all znodes are persistent.

Ephemeral znodes (flag: e) may be routinely deleted while a session expires or whilst the patron disconnects.
Sequential znodes guaranty that the znode direction will be particular.
ZooKeeper ensemble will upload collection variety at the side of 10 digit padding to the znode direction. For example, the znode course /myapp could be transformed to /myapp0000000001 and the subsequent sequence quantity might be /myapp0000000002.
If no flags are unique, then the znode is considered as continual.

Create /direction /statistics

To create a Sequential znode, upload -s flag as proven underneath.

Create -s /course /statistics

To create an Ephemeral Znode, upload -e flag as shown below.

Create -e /path /statistics

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Question 10. How Can We Create Children / Sub-znode?

Answer :

Creating youngsters is much like growing new znodes. The most effective distinction is that the direction of the child znode may have the figure course as nicely.

Create /parent/course/subnode/direction /statistics

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Question 11. How Can We Remove A Znode?

Answer :

Removes a distinctive znode and recursively all its kids. This might show up most effective if this kind of znode is to be had.

Rmr /path

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Question 12. What Are The Basics Of Zookeeper Api?

Answer :

Application interacting with ZooKeeper ensemble is referred as ZooKeeper Client or in reality Client. Znode is the core thing of ZooKeeper ensemble and ZooKeeper API gives a small set of techniques to control all of the details of znode with ZooKeeper ensemble. A client need to observe the steps given underneath to have a clear and smooth interaction with ZooKeeper ensemble.

Connect to the ZooKeeper ensemble. ZooKeeper ensemble assign a Session ID for the patron.
Send heartbeats to the server periodically. Otherwise, the ZooKeeper ensemble expires the Session ID and the consumer desires to reconnect.
Get / Set the znodes so long as a session ID is lively.
Disconnect from the ZooKeeper ensemble, once all of the duties are finished. If the client is inactive for a extended time, then the ZooKeeper ensemble will automatically disconnect the customer.
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Question 13. Explain The Methods Of Zookeeperclass?

Answer :

The principal a part of the ZooKeeper API is ZooKeeper elegance. It presents alternatives to attach the ZooKeeper ensemble in its constructor and has the following methods -

join - connect to the ZooKeeper ensemble

ZooKeeper(String connectionString, int sessionTimeout, Watcher watcher)

create - create a znode

create(String path, byte[] facts, List acl, CreateMode createMode)

exists - test whether or not a znode exists and its records

exists(String course, boolean watcher)

getData - get data from a particular znode

getData(String path, Watcher watcher, Stat stat)

setData - set information in a particular znode

setData(String direction, byte[] facts, int model)

getChildren - get all sub-nodes to be had in a selected znode

getChildren(String direction, Watcher watcher)

delete - get a specific znode and all its children

delete(String route, int model)

close - close a connection

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Question 14. Mention Some Instances Where Zookeeper Is Using?

Answer :

Below are a number of instances in which Apache ZooKeeper is being applied:

Apache Storm, being a actual time stateless processing/computing framework, manages its country in ZooKeeper Service
Apache Kafka makes use of it for selecting chief node for the topic walls
Apache YARN is based on it for the automated failover of useful resource supervisor (grasp node)
Yahoo! Utilties it because the coordination and failure recovery service for Yahoo! Message Broker, which is a quite scalable post-subscribe device dealing with thousands of topics for replication and facts delivery. It is utilized by the Fetching Service for Yahoo! Crawler, in which it additionally manages failure recuperation.