Amazon ElastiCache
ElastiCache for Memcached User Guide (API Version 2015-02-02)

Adding Nodes to a Cluster

Adding nodes to a Memcached cluster increases the number of you cluster's partitions. When you change the number of partitions in a cluster some of your key spaces need to be remapped so that they are mapped to the right node. Remapping key spaces temporarily increases the number of cache misses on the cluster. For more information, see Configuring Your ElastiCache Client for Efficient Load Balancing.

You can use the ElastiCache Management Console, the AWS CLI or ElastiCache API to add nodes to your cluster.

Using the AWS Management Console

To add nodes to a cluster (console)

The following procedure can be used to add nodes to a cluster.

  1. Sign in to the AWS Management Console and open the ElastiCache console at https://console.aws.amazon.com/elasticache/.

  2. In the navigation pane, choose the engine running on the cluster you want to add nodes to.

    A list of clusters running the chosen engine appears.

  3. From the list of clusters, choose the name of the cluster, not the box to the left of the cluster's name, you want to add a node to.

  4. Choose Add node.

  5. Complete the information requested in the Add Node dialog box.

  6. Choose the Apply Immediately - Yes button to add this node immediately, or choose No to add this node during the cluster's next maintenance window.

    Impact of New Add and Remove Requests on Pending Requests

    Scenarios Pending Operation New Request Results

    Scenario 1

    Delete

    Delete

    The new delete request, pending or immediate, replaces the pending delete request.

    For example, if nodes 0001, 0003, and 0007 are pending deletion and a new request to delete nodes 0002 and 0004 is issued, only nodes 0002 and 0004 will be deleted. Nodes 0001, 0003, and 0007 will not be deleted.

    Scenario 2

    Delete

    Create

    The new create request, pending or immediate, replaces the pending delete request.

    For example, if nodes 0001, 0003, and 0007 are pending deletion and a new request to create a node is issued, a new node will be created and nodes 0001, 0003, and 0007 will not be deleted.

    Scenario 3

    Create

    Delete

    The new delete request, pending or immediate, replaces the pending create request.

    For example, if there is a pending request to create two nodes and a new request is issued to delete node 0003, no new nodes will be created and node 0003 will be deleted.

    Scenario 4

    Create

    Create

    The new create request is added to the pending create request.

    For example, if there is a pending request to create two nodes and a new request is issued to create three nodes, the new requests is added to the pending request and five nodes will be created.

    Important

    If the new create request is set to Apply Immediately - Yes, all create requests are performed immediately. If the new create request is set to Apply Immediately - No, all create requests are pending.

    To determine what operations are pending, choose the Description tab and check to see how many pending creations or deletions are shown. You cannot have both pending creations and pending deletions.

    
	   Image: Cluster description tab
  7. Choose the Add button.

    After a few moments, the new nodes should appear in the nodes list with a status of creating. If they don't appear, refresh your browser page. When the node's status changes to available the new node is able to be used.

Using the AWS CLI

To add nodes to a cluster using the AWS CLI, use the AWS CLI operation modify-cache-cluster with the following parameters:

  • --cache-cluster-id The ID of the cache cluster you want to add nodes to.

  • --num-cache-nodes The --num-cache-nodes parameter specifies the number of nodes you want in this cluster after the modification is applied. To add nodes to this cluster, --num-cache-nodes must be greater than the current number of nodes in this cluster. If this value is less than the current number of nodes, ElastiCache expects the parameter cache-node-ids-to-remove and a list of nodes to remove from the cluster. For more information, see Using the AWS CLI.

  • --apply-immediately or --no-apply-immediately which specifies whether to add these nodes immediately or at the next maintenance window.

For Linux, macOS, or Unix:

aws elasticache modify-cache-cluster \ --cache-cluster-id my-cluster \ --num-cache-nodes 5 \ --apply-immediately

For Windows:

aws elasticache modify-cache-cluster ^ --cache-cluster-id my-cluster ^ --num-cache-nodes 5 ^ --apply-immediately

This operation produces output similar to the following (JSON format):

{ "CacheCluster": { "Engine": "memcached", "CacheParameterGroup": { "CacheNodeIdsToReboot": [], "CacheParameterGroupName": "default.memcached1.4", "ParameterApplyStatus": "in-sync" }, "CacheClusterId": "my-cluster", "PreferredAvailabilityZone": "us-west-2b", "ConfigurationEndpoint": { "Port": 11211, "Address": "rlh-mem000.7alc7bf-example.cfg.usw2.cache.amazonaws.com" }, "CacheSecurityGroups": [], "CacheClusterCreateTime": "2016-09-21T16:28:28.973Z", "AutoMinorVersionUpgrade": true, "CacheClusterStatus": "modifying", "NumCacheNodes": 2, "ClientDownloadLandingPage": "https://console.aws.amazon.com/elasticache/home#client-download:", "SecurityGroups": [ { "Status": "active", "SecurityGroupId": "sg-dbe93fa2" } ], "CacheSubnetGroupName": "default", "EngineVersion": "1.4.24", "PendingModifiedValues": { "NumCacheNodes": 5 }, "PreferredMaintenanceWindow": "sat:09:00-sat:10:00", "CacheNodeType": "cache.m3.medium" } }

For more information, see the AWS CLI topic modify-cache-cluster.

Using the ElastiCache API

To add nodes to a cluster (ElastiCache API)

  • Call the ModifyCacheCluster API operation with the following parameters:

    • CacheClusterId The ID of the cluster you want to add nodes to.

    • NumCacheNodes The NumCachNodes parameter specifies the number of nodes you want in this cluster after the modification is applied. To add nodes to this cluster, NumCacheNodes must be greater than the current number of nodes in this cluster. If this value is less than the current number of nodes, ElastiCache expects the parameter CacheNodeIdsToRemove with a list of nodes to remove from the cluster (see Using the ElastiCache API).

    • ApplyImmediately Specifies whether to add these nodes immediately or at the next maintenance window.

    • Region Specifies the AWS region of the cluster you want to add nodes to.

    The following example shows a call to add nodes to a cluster.

    https://elasticache.us-west-2.amazonaws.com/ ?Action=ModifyCacheCluster &ApplyImmediately=true &NumCacheNodes=5 &CacheClusterId=my-cluster &Region=us-east-2 &Version=2014-12-01 &SignatureVersion=4 &SignatureMethod=HmacSHA256 &Timestamp=20141201T220302Z &X-Amz-Algorithm=AWS4-HMAC-SHA256 &X-Amz-Date=20141201T220302Z &X-Amz-SignedHeaders=Host &X-Amz-Expires=20141201T220302Z &X-Amz-Credential=<credential> &X-Amz-Signature=<signature>

For more information, see ElastiCache API topic ModifyCacheCluster.