Extending a Cluster by Adding Nodes

This section describes how to add capacity to a MapR cluster by adding nodes.

You add nodes to a cluster by using the web-based MapR Installer (version 1.6 or later) or MapR Installer Stanzas. The nodes are added to a pre-existing group online without disturbing the running cluster. You can add nodes to on-premise clusters or to cloud-based clusters.

You can add multiple nodes to a group in the same operation, and you can add nodes to custom groups. You can also add the same node to multiple groups. The MapR Installer installs the new nodes with the same patch level as the existing nodes.

Note: Before adding nodes, use the MapR Installer to ensure that your cluster uses three-digit MEPs. If your cluster uses two-digit MEPs, adding a node can result in a version mismatch between the cluster and the newly added node. To change from two-digit to three-digit MEPs you can perform an Incremental Install using the MapR Installer. For more information, see Understanding Two-Digit and Three-Digit MEPs.

Restrictions

Note these restrictions for using the Extend Cluster operation. When adding nodes:
  • The cluster must already be installed before nodes can be added.
  • You cannot add a node to a MASTER group, since these services can run only on one node.
  • If you add a node to a CONTROL group that has a CLDB, you must do a manual, rolling restart of the entire cluster.
  • If you add a node to a group that has OpenTSDB, you must add the same node to the group that contains AsyncHBase (currently, the MapR Installer does not check to ensure that this dependency is met).
  • You cannot add services.
  • You cannot change the MEP version or MapR Core version.
  • You cannot add new service groups.
  • New nodes are added automatically to the DEFAULT group.
  • A node added to a MapR secure cluster will be configured for security automatically. If the cluster is custom secure, you cannot use the MapR Installer. See Customizing Security in MapR.

Before Adding Nodes

  1. Determine the group(s) to which new nodes will be added.
    You can add nodes to the following types of groups:
    • CLIENT
    • DATA
    • CONTROL
    • MULTI_MASTER
    • MONITORING_MASTER
    Note: If you add a node to a group containing a CLDB, you must restart all the nodes except for the new node. If you add a node to a group containing Zookeeper (but not CLDB), you must restart Zookeeper on all the Zookeeper nodes except for the new node. And you must restart the lead Zookeeper last.
    To gather information about groups, see Getting Information About Services and Groups.
  2. Ensure that the node(s) to be added meet the installation prerequisites described in the MapR Installer Prerequisites and Guidelines.

Adding Nodes Using the MapR Installer Web Interface

  1. Use a browser to connect to the cluster using the MapR Installer URL:
    https://<Installer Node hostname/IPaddress>:9443
  2. On the status screen, click the Extend Cluster button. The MapR Installer displays the Extend Cluster screen showing the currently configured groups and services.
    Note: If the Extend Cluster button is not visible, you might need to clear your browser cache and refresh the browser page.
  3. Specify the nodes to be added:
    • On-Premise Cluster
      In the Additional Nodes column, specify the host name(s) or IP address(es) of the nodes to be added. If you are adding multiple nodes, you can specify an array. The following example adds perfnode132.perf.lab and perfnode133.perf.lab to the CONTROL group and perfnode132.perf.lab to the MULTI_MASTER group:

    • Cloud-Based Cluster
      In the Additional Nodes column, specify the number of nodes to be added. You do not need to specify the host name or IP address. The following example adds a node to each of the CONTROL, DATA, and CLIENT groups:

  4. Click Next. The MapR Installer checks the nodes to ensure that they are ready for installation and displays the Authentication screen.
  5. Enter your SSH password and other authentication information as needed, and click Next. The installer displays the Verify Nodes screen.
    Note: For a cloud-based cluster, the Authentication screen requests information that is specific to the type of cluster (AWS or Azure). Use the tooltips to learn more about the authentication information needed for your cluster.
  6. Click a node icon to check the node status and see warnings or error information in the right pane. The node-icon color reflects the installation readiness for each node:
    • Green (ready to install)
    • Yellow (warning)
    • Red (cannot install)
    Note: If there are warnings or errors, hold your cursor over the warning or error in the right pane to see more information.
    Important: If node verification fails, try removing the node and retrying the operation. If node verification fails and you abort the installation, you must use the Import State command to reset the cluster to the last known state. Otherwise, you will not be able to perform subsequent MapR Installer operations. See Importing or Exporting the Cluster State.
  7. When you are satisfied that the nodes are ready to be installed, click Next. The MapR Installer addes the nodes. After the nodes are added, you can use the MapR Control System (MCS) to view the nodes in the cluster.
  8. Perform any post-expansion steps. Post-expansion steps are necessary only if you added a node to a group containing a CLDB or Zookeeper.
    If you added a node to a group containing . . . Do this
    Zookeeper only One node at a time, stop and restart the Zookeeper service on all Zookeeper nodes, restarting the master Zookeeper node last. You do not need to restart the Zookeeper node that was added. See Post-Expansion Steps for Extending a Cluster.
    Zookeeper and CLDB

    or

    CLDB only

    One node at a time, restart all services on all nodes following the order prescribed in Manual Rolling Upgrade Description. You do not need to restart the node that was added. See Post-Expansion Steps for Extending a Cluster.

Adding Nodes Using a MapR Installer Stanza

To add nodes using a MapR Installer Stanza, you add the scaled_hosts2: parameter (on-premise clusters) or the scaled_count: parameter (cloud-based clusters) to the Stanza file for the group that you want to scale. Then you run the Stanza using the install command. The services contained in the group are configured for the added node.
Note: If the group you are trying to scale does not contain the mapr-core-5.2.x service, the first group containing mapr-core-5.2.x will automatically get scaled.
  1. In the Stanza file, add the scaled_hosts2: or scaled_count: parameter:
    • On-Premise Cluster

      Add the scaled_hosts2: parameter to the group that you want to scale, specifying the host name(s) or IP address(s) of the nodes to be added. In the following example, the perfnode132.perf.lab node is added to the CLIENT group:

      Stanza Before Scaling Modified Stanza with scaled_hosts2 Parameter (On-Premise Cluster)
      groups:
      - hosts:
         - perfnode131.perf.lab
         label: CLIENT
      - services: 
          - mapr-spark-client-2.0.1
          - mapr-hive-client-1.2
          - mapr-hbase-1.1
          - mapr-asynchbase-1.7.0
          - mapr-kafka-0.9.0
      groups:
      - hosts:
         - perfnode131.perf.lab
         label: CLIENT
         scaled_hosts2:
         - perfnode132.perf.lab
      - services:
          - mapr-spark-client-2.0.1
          - mapr-hive-client-1.2
          - mapr-hbase-1.1
          - mapr-asynchbase-1.7.0
          - mapr-kafka-0.9.0
    • Cloud-Based Cluster

      Add the scaled_count: parameter to the group that you want to scale. Include a number after the parameter to indicate the number of additional nodes to be added to the group. You do not need to specify the host names or IP addresses of the nodes to be added. In the following example, one additional node is added to the CLIENT group:

      Stanza Before Scaling Modified Stanza with scaled_count Parameter (Cloud-Based Cluster)
      groups:
      - hosts:
         - perfnode131.perf.lab
         label: CLIENT
      - services: 
          - mapr-spark-client-2.0.1
          - mapr-hive-client-1.2
          - mapr-hbase-1.1
          - mapr-asynchbase-1.7.0
          - mapr-kafka-0.9.0
      groups:
      - hosts:
         - perfnode131.perf.lab
         label: CLIENT
         scaled_count: 1
      - services:
          - mapr-spark-client-2.0.1
          - mapr-hive-client-1.2
          - mapr-hbase-1.1
          - mapr-asynchbase-1.7.0
          - mapr-kafka-0.9.0
  2. Run the Stanza file using the install command. See Installing or Upgrading MapR Core Using a MapR Installer Stanza. The MapR Installer SDK detects the new scaled_host(s) and gives you the option to proceed with the installation or cancel.
  3. Perform any post-expansion steps. Post-expansion steps are necessary only if you added a node to group containing a CLDB or Zookeeper.
    If you added a node to a group containing . . . Do this
    Zookeeper only One node at a time, stop and restart the Zookeeper service on all Zookeeper nodes, restarting the master Zookeeper node last. You do not need to restart the Zookeeper node that was added. See Post-Expansion Steps for Extending a Cluster.
    Zookeeper and CLDB

    or

    CLDB only

    One node at a time, restart all services on all nodes following the order prescribed in Manual Rolling Upgrade Description. You do not need to restart the node that was added. See Post-Expansion Steps for Extending a Cluster.