Intuit Most Frequently Asked Latest Hadoop Interview Questions Answers
Explain about the different channel types in Flume. Which channel type is faster?
The 3 different built in channel types available in Flume are-
MEMORY Channel – Events are read from the source into memory and passed to the sink.
JDBC Channel – JDBC Channel stores the events in an embedded Derby database.
FILE Channel –File Channel writes the contents to a file on the file system after reading the event from a source. The file is deleted only after the contents are successfully delivered to the sink.
MEMORY Channel is the fastest channel among the three however has the risk of data loss. The channel that you choose completely depends on the nature of the big data application and the value of each event.
Which is the reliable channel in Flume to ensure that there is no data loss?
FILE Channel is the most reliable channel among the 3 channels JDBC, FILE and MEMORY.
Explain about the replication and multiplexing selectors in Flume.
Channel Selectors are used to handle multiple channels. Based on the Flume header value, an event can be written just to a single channel or to multiple channels. If a channel selector is not specified to the source then by default it is the Replicating selector. Using the replicating selector, the same event is written to all the channels in the source’s channels list. Multiplexing channel selector is used when the application has to send different events to different channels.
How multi-hop agent can be setup in Flume?
Avro RPC Bridge mechanism is used to setup Multi-hop agent in Apache Flume.
Does Apache Flume provide support for third party plug-ins?
Most of the data analysts use Apache Flume has plug-in based architecture as it can load data from external sources and transfer it to external destinations.
Is it possible to leverage real time analysis on the big data collected by Flume directly? If yes, then explain how.
Data from Flume can be extracted, transformed and loaded in real-time into Apache Solr servers using MorphlineSolrSink
Differentiate between FileSink and FileRollSink
The major difference between HDFS FileSink and FileRollSink is that HDFS File Sink writes the events into the Hadoop Distributed File System (HDFS) whereas File Roll Sink stores the events into the local file system.
Can Apache Kafka be used without Zookeeper?
It is not possible to use Apache Kafka without Zookeeper because if the Zookeeper is down Kafka cannot serve client request.
What problems can be addressed by using Zookeeper?
In the development of distributed systems, creating own protocols for coordinating the hadoop cluster results in failure and frustration for the developers. The architecture of a distributed system can be prone to deadlocks, inconsistency and race conditions. This leads to various difficulties in making the hadoop cluster fast, reliable and scalable. To address all such problems, Apache ZooKeeper can be used as a coordination service to write correct distributed applications without having to reinvent the wheel from the beginning.
What are active and passive “NameNodes”?
In HA (High Availability) architecture, we have two NameNodes – Active “NameNode” and Passive “NameNode”.
Active “NameNode” is the “NameNode” which works and runs in the cluster.
Passive “NameNode” is a standby “NameNode”, which has similar data as active “NameNode”.
When the active “NameNode” fails, the passive “NameNode” replaces the active “NameNode” in the cluster. Hence, the cluster is never without a “NameNode” and so it never fails.
Why does one remove or add nodes in a Hadoop cluster frequently?
One of the most attractive features of the Hadoop framework is its utilization of commodity hardware. However, this leads to frequent “DataNode” crashes in a Hadoop cluster. Another striking feature of Hadoop Framework is the ease of scale in accordance with the rapid growth in data volume. Because of these two reasons, one of the most common task of a Hadoop administrator is to commission (Add) and decommission (Remove) “Data Nodes” in a Hadoop Cluster.
What happens when two clients try to access the same file in the HDFS?
HDFS supports exclusive writes only.
When the first client contacts the “NameNode” to open the file for writing, the “NameNode” grants a lease to the client to create this file. When the second client tries to open the same file for writing, the “NameNode” will notice that the lease for the file is already granted to another client, and will reject the open request for the second client.
How does NameNode tackle DataNode failures?
NameNode periodically receives a Heartbeat (signal) from each of the DataNode in the cluster, which implies DataNode is functioning properly.
A block report contains a list of all the blocks on a DataNode. If a DataNode fails to send a heartbeat message, after a specific period of time it is marked dead.
The NameNode replicates the blocks of dead node to another DataNode using the replicas created earlier.
What will you do when NameNode is down?
The NameNode recovery process involves the following steps to make the Hadoop cluster up and running:
Use the file system metadata replica (FsImage) to start a new NameNode.
Then, configure the DataNodes and clients so that they can acknowledge this new NameNode, that is started.
Now the new NameNode will start serving the client after it has completed loading the last checkpoint FsImage (for metadata information) and received enough block reports from the DataNodes.
Name a few companies that use Zookeeper.
Yahoo, Solr, Helprace, Neo4j, Rackspace
What is the role of Zookeeper in HBase architecture?
In HBase architecture, ZooKeeper is the monitoring server that provides different services like –tracking server failure and network partitions, maintaining the configuration information, establishing communication between the clients and region servers, usability of ephemeral nodes to identify the available servers in the cluster.
Explain about ZooKeeper in Kafka
Apache Kafka uses ZooKeeper to be a highly distributed and scalable system. Zookeeper is used by Kafka to store various configurations and use them across the hadoop cluster in a distributed manner. To achieve distributed-ness, configurations are distributed and replicated throughout the leader and follower nodes in the ZooKeeper ensemble. We cannot directly connect to Kafka by bye-passing ZooKeeper because if the ZooKeeper is down it will not be able to serve the client request.
Explain how Zookeeper works
ZooKeeper is referred to as the King of Coordination and distributed applications use ZooKeeper to store and facilitate important configuration information updates. ZooKeeper works by coordinating the processes of distributed applications. ZooKeeper is a robust replicated synchronization service with eventual consistency. A set of nodes is known as an ensemble and persisted data is distributed between multiple nodes.
3 or more independent servers collectively form a ZooKeeper cluster and elect a master. One client connects to any of the specific server and migrates if a particular node fails. The ensemble of ZooKeeper nodes is alive till the majority of nods are working. The master node in ZooKeeper is dynamically selected by the consensus within the ensemble so if the master node fails then the role of master node will migrate to another node which is selected dynamically. Writes are linear and reads are concurrent in ZooKeeper.
List some examples of Zookeeper use cases.
Found by Elastic uses Zookeeper comprehensively for resource allocation, leader election, high priority notifications and discovery. The entire service of Found built up of various systems that read and write to Zookeeper.
Apache Kafka that depends on ZooKeeper is used by LinkedIn
Storm that relies on ZooKeeper is used by popular companies like Groupon and Twitter.
How to use Apache Zookeeper command line interface?
ZooKeeper has a command line client support for interactive use. The command line interface of ZooKeeper is similar to the file and shell system of UNIX. Data in ZooKeeper is stored in a hierarchy of Znodes where each znode can contain data just similar to a file. Each znode can also have children just like directories in the UNIX file system.
Zookeeper-client command is used to launch the command line client. If the initial prompt is hidden by the log messages after entering the command, users can just hit ENTER to view the prompt.
Explain about the different channel types in Flume. Which channel type is faster?
The 3 different built in channel types available in Flume are-
MEMORY Channel – Events are read from the source into memory and passed to the sink.
JDBC Channel – JDBC Channel stores the events in an embedded Derby database.
FILE Channel –File Channel writes the contents to a file on the file system after reading the event from a source. The file is deleted only after the contents are successfully delivered to the sink.
MEMORY Channel is the fastest channel among the three however has the risk of data loss. The channel that you choose completely depends on the nature of the big data application and the value of each event.
Which is the reliable channel in Flume to ensure that there is no data loss?
FILE Channel is the most reliable channel among the 3 channels JDBC, FILE and MEMORY.
Explain about the replication and multiplexing selectors in Flume.
Channel Selectors are used to handle multiple channels. Based on the Flume header value, an event can be written just to a single channel or to multiple channels. If a channel selector is not specified to the source then by default it is the Replicating selector. Using the replicating selector, the same event is written to all the channels in the source’s channels list. Multiplexing channel selector is used when the application has to send different events to different channels.
How multi-hop agent can be setup in Flume?
Avro RPC Bridge mechanism is used to setup Multi-hop agent in Apache Flume.
Does Apache Flume provide support for third party plug-ins?
Most of the data analysts use Apache Flume has plug-in based architecture as it can load data from external sources and transfer it to external destinations.
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| Intuit Most Frequently Asked Latest Hadoop Interview Questions Answers |
Is it possible to leverage real time analysis on the big data collected by Flume directly? If yes, then explain how.
Data from Flume can be extracted, transformed and loaded in real-time into Apache Solr servers using MorphlineSolrSink
Differentiate between FileSink and FileRollSink
The major difference between HDFS FileSink and FileRollSink is that HDFS File Sink writes the events into the Hadoop Distributed File System (HDFS) whereas File Roll Sink stores the events into the local file system.
Can Apache Kafka be used without Zookeeper?
It is not possible to use Apache Kafka without Zookeeper because if the Zookeeper is down Kafka cannot serve client request.
What problems can be addressed by using Zookeeper?
In the development of distributed systems, creating own protocols for coordinating the hadoop cluster results in failure and frustration for the developers. The architecture of a distributed system can be prone to deadlocks, inconsistency and race conditions. This leads to various difficulties in making the hadoop cluster fast, reliable and scalable. To address all such problems, Apache ZooKeeper can be used as a coordination service to write correct distributed applications without having to reinvent the wheel from the beginning.
What are active and passive “NameNodes”?
In HA (High Availability) architecture, we have two NameNodes – Active “NameNode” and Passive “NameNode”.
Active “NameNode” is the “NameNode” which works and runs in the cluster.
Passive “NameNode” is a standby “NameNode”, which has similar data as active “NameNode”.
When the active “NameNode” fails, the passive “NameNode” replaces the active “NameNode” in the cluster. Hence, the cluster is never without a “NameNode” and so it never fails.
Why does one remove or add nodes in a Hadoop cluster frequently?
One of the most attractive features of the Hadoop framework is its utilization of commodity hardware. However, this leads to frequent “DataNode” crashes in a Hadoop cluster. Another striking feature of Hadoop Framework is the ease of scale in accordance with the rapid growth in data volume. Because of these two reasons, one of the most common task of a Hadoop administrator is to commission (Add) and decommission (Remove) “Data Nodes” in a Hadoop Cluster.
What happens when two clients try to access the same file in the HDFS?
HDFS supports exclusive writes only.
When the first client contacts the “NameNode” to open the file for writing, the “NameNode” grants a lease to the client to create this file. When the second client tries to open the same file for writing, the “NameNode” will notice that the lease for the file is already granted to another client, and will reject the open request for the second client.
How does NameNode tackle DataNode failures?
NameNode periodically receives a Heartbeat (signal) from each of the DataNode in the cluster, which implies DataNode is functioning properly.
A block report contains a list of all the blocks on a DataNode. If a DataNode fails to send a heartbeat message, after a specific period of time it is marked dead.
The NameNode replicates the blocks of dead node to another DataNode using the replicas created earlier.
What will you do when NameNode is down?
The NameNode recovery process involves the following steps to make the Hadoop cluster up and running:
Use the file system metadata replica (FsImage) to start a new NameNode.
Then, configure the DataNodes and clients so that they can acknowledge this new NameNode, that is started.
Now the new NameNode will start serving the client after it has completed loading the last checkpoint FsImage (for metadata information) and received enough block reports from the DataNodes.
Name a few companies that use Zookeeper.
Yahoo, Solr, Helprace, Neo4j, Rackspace
What is the role of Zookeeper in HBase architecture?
In HBase architecture, ZooKeeper is the monitoring server that provides different services like –tracking server failure and network partitions, maintaining the configuration information, establishing communication between the clients and region servers, usability of ephemeral nodes to identify the available servers in the cluster.
Explain about ZooKeeper in Kafka
Apache Kafka uses ZooKeeper to be a highly distributed and scalable system. Zookeeper is used by Kafka to store various configurations and use them across the hadoop cluster in a distributed manner. To achieve distributed-ness, configurations are distributed and replicated throughout the leader and follower nodes in the ZooKeeper ensemble. We cannot directly connect to Kafka by bye-passing ZooKeeper because if the ZooKeeper is down it will not be able to serve the client request.
Explain how Zookeeper works
ZooKeeper is referred to as the King of Coordination and distributed applications use ZooKeeper to store and facilitate important configuration information updates. ZooKeeper works by coordinating the processes of distributed applications. ZooKeeper is a robust replicated synchronization service with eventual consistency. A set of nodes is known as an ensemble and persisted data is distributed between multiple nodes.
3 or more independent servers collectively form a ZooKeeper cluster and elect a master. One client connects to any of the specific server and migrates if a particular node fails. The ensemble of ZooKeeper nodes is alive till the majority of nods are working. The master node in ZooKeeper is dynamically selected by the consensus within the ensemble so if the master node fails then the role of master node will migrate to another node which is selected dynamically. Writes are linear and reads are concurrent in ZooKeeper.
List some examples of Zookeeper use cases.
Found by Elastic uses Zookeeper comprehensively for resource allocation, leader election, high priority notifications and discovery. The entire service of Found built up of various systems that read and write to Zookeeper.
Apache Kafka that depends on ZooKeeper is used by LinkedIn
Storm that relies on ZooKeeper is used by popular companies like Groupon and Twitter.
How to use Apache Zookeeper command line interface?
ZooKeeper has a command line client support for interactive use. The command line interface of ZooKeeper is similar to the file and shell system of UNIX. Data in ZooKeeper is stored in a hierarchy of Znodes where each znode can contain data just similar to a file. Each znode can also have children just like directories in the UNIX file system.
Zookeeper-client command is used to launch the command line client. If the initial prompt is hidden by the log messages after entering the command, users can just hit ENTER to view the prompt.
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