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Remove a Node and Rebalance

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      Enterprise Analytics allows a cluster node to be removed, and the remaining nodes rebalanced.

      Understanding Removal and Rebalance

      The rebalance operation redistributes query workloads and responsibility for storage partitions across available cluster nodes to in optimal fashion. This allows the best possible data-availability to be maintained after nodes have been added or removed. Examples of using rebalance after node-addition have already been provided, in Add a Node and Rebalance and Join a Cluster and Rebalance.

      Nodes can also be rebalanced following removal: this is demonstrated in the current section.

      This page provides the steps to be taken for node-removal and rebalance. For a conceptual explanation of removal, see Removal.

      Connectivity Considerations

      When removing a node from a cluster, it is important to follow the connectivity best practices outlined in Cluster Connectivity and Topology Management. The scale in procedures vary based on the addressing model in use (Active Load Balancer, Passive Load Balancer, or DNS-Only). To minimize disruptions to client applications, ensure that you follow the procedures detailed in Scale In (Remove Node) section.

      Examples on This Page

      The examples in the subsections below show how to remove the same node from the same two-node cluster; using the UI, the CLI, and the REST API respectively. The examples assume:

      • A two-node cluster already exists; as at the conclusion of List Cluster Nodes.

      • The cluster has the Full Administrator username of Administrator, and password of password.

      Remove a Node with the UI

      Proceed as follows:

      1. Access the Servers screen of Enterprise Analytics Web Console by clicking on the Servers tab in the left-hand navigation bar. The screen displays the two-node cluster with both nodes 10.142.181.101 and 10.142.181.102 listed in a tabular format showing their current status, services, resource utilization, and data distribution.

      2. Click on the row for node 10.142.181.102 to expand it and reveal additional details. The row expands vertically to show comprehensive information about the node including:

        • Node details (name, version, uptime, OS)

        • Service configurations and RAM quotas

        • Address and security settings

        • Current resource utilization metrics

      3. To initiate removal, click on the Remove button located at the lower left of the expanded row. This button allows you to flag the node for removal from the cluster.

        The Confirm Server Removal dialog appears, asking you to confirm the removal operation. The dialog warns about the implications of removing the node and requests confirmation that you want to proceed.

        Click on the Remove Server confirmation button to proceed. The Servers screen reappears showing that node 10.142.181.102 has been flagged for removal. The node status now indicates that it is "flagged for removal" and is "Still available to take traffic". A rebalance must be performed to complete removal.

      4. Click on the Rebalance button at the upper right of the screen to begin the rebalancing process. Rebalancing now occurs, redistributing the data from the node being removed to the remaining nodes in the cluster.

        A progress dialog appears providing status information about the rebalance operation, including: - Progress bars showing completion percentage.

      If rebalance fails, notifications are duly provided.

      These are described in Rebalance Failure Notification.

      See also the information provided on Automated Rebalance-Failure Handling, and the procedure for its set-up, described in Rebalance Settings.

      Remove a Node with the CLI

      A node can be removed from the cluster by means of the CLI. Note that the node does not have to be failed over prior to removal.

      To remove the node and perform the necessary rebalance, use the rebalance command with the --server-remove option.

      /opt/enterprise-analytics/bin/couchbase-cli
--username Administrator \
--password password --server-remove 10.0.0.1:8091

      This initiates the rebalance process. As it continues, progress is shown as console output:

      Rebalancing
[================================                 ] 31.67%

      For more information, see the command reference for rebalance.

      Remove a Node with the REST API

      To remove a node from a cluster with the REST API, and rebalance the remaining nodes, use the /controller/rebalance URI. This requires that all known nodes be specified, and that the nodes to be ejected also be specified:

      curl  -u Administrator:password -v -X POST \
http://10.142.181.101:8091/controller/rebalance \
-d 'ejectedNodes=ns_1%4010.142.181.102' \
-d 'knownNodes=ns_1%4010.142.181.101%2Cns_1%4010.142.181.102'

      The command returns no output.

      Next Steps

      Nodes can be failed over, so that an unhealthy or unresponsive node can be removed from the cluster without application-access being affected. See Fail Nodes Over.