What is high availability in Hadoop?

The high availability feature in Hadoop ensures the availability of the Hadoop cluster without any downtime, even in unfavorable conditions like NameNode failure, DataNode failure, machine crash, etc. It means if the machine crashes, data will be accessible from another path.

How does Hadoop achieve high availability?

Hadoop HDFS provides High availability of data. When the client requests NameNode for data access, then the NameNode searches for all the nodes in which that data is available. After that, it provides access to that data to the user from the node in which data was quickly available.

How do I enable high availability in HDFS?

Setting Up and Configuring High Availability Cluster in Hadoop:

  1. Extract the Hadoop tar ball.
  2. Generate the SSH key in all the nodes.
  3. In Active Namenode, copy the id_rsa.
  4. Copy the NameNode public key to all the nodes using ssh-copy-id command.
  5. Copy NameNode public key to data node.

What is JournalNode Hadoop?

JournalNode is a daemon that enable high availbility of namenode. In a typical HA cluster, two separate machines are configured as NameNodes. At any point in time, exactly one of the NameNodes is in an Active state, and the other is in a Standby state.

What is failover in HDFS?

Automatic Failover – Automatic Failover is the process in which system automatically transfers its control to the standby NameNode when the NameNode fails. In Hadoop Automatic failover occurs in case of NameNode failures. But in the case of NameNode failure, Failover will start automatically.

How many NameNodes are there in HDFS?

You can have only a single name node in a cluster. Detail – In Yarn / Hadoop 2.0 they have come with a concept of active name node and standby name node. ( This is where most of the people get confused. They consider them to be 2 nodes in a cluster).

What is SerDe in Hadoop?

The SerDe interface allows you to instruct Hive about how a record should be processed. A SerDe is a combination of a Serializer and a Deserializer. Hive uses SerDe (and FileFormat) to read and write the table’s row.

What is Nameservice in Hadoop?

dfs.client.failover.proxy.provider.[nameservice ID] – the Java class that HDFS clients use to contact the Active NameNode. Configure the name of the Java class which will be used by the DFS Client to determine which NameNode is the current Active, and therefore which NameNode is currently serving client requests.

What is Fsimage and Editlog?

FSimage is a point-in-time snapshot of HDFS’s namespace. Edit log records every changes from the last snapshot. The last snapshot is actually stored in FSImage.

How can you ensure high availability of name node?

  1. Configure Manual or Automatic ResourceManager Failover.
  2. Deploy the ResourceManager HA Cluster.
  3. Minimum Settings for Automatic ResourceManager HA Configuration.
  4. Testing ResourceManager HA on a Single Node.
  5. Deploy Hue with a ResourceManager HA Cluster.

What is high availability in name node?

HDFS NameNode High Availability architecture provides the option of running two redundant NameNodes in the same cluster in an active/passive configuration with a hot standby.

How many DataNodes can be run on a single Hadoop?

With 100 DataNodes in a cluster, 64GB of RAM on the NameNode provides plenty of room to grow the cluster.”