# Changing the number of replicas You can dynamically increase or decrease the number of read replicas in your Valkey or Redis OSS replication group using the AWS Management Console, the AWS CLI, or the ElastiCache API. If your replication group is a Valkey or Redis OSS (cluster mode enabled) replication group, you can choose which shards (node groups) to increase or decrease the number of replicas. To dynamically change the number of replicas in your replication group, choose the operation from the following table that fits your situation. | To Do This | For Valkey or Redis OSS (cluster mode enabled) | For Valkey or Redis OSS (cluster mode disabled) | | --- | --- | --- | | Add replicas | [Increasing the number of replicas in a shard](increase-replica-count.md) | [Increasing the number of replicas in a shard](increase-replica-count.md) [Adding a read replica for Valkey or Redis OSS (Cluster Mode Disabled)](Replication.AddReadReplica.md) | | Delete replicas | [Decreasing the number of replicas in a shard](decrease-replica-count.md) | [Decreasing the number of replicas in a shard](decrease-replica-count.md) [Deleting a read replica for Valkey or Redis OSS (Cluster Mode Disabled)](Replication.RemoveReadReplica.md) | # Increasing the number of replicas in a shard You can increase the number of replicas in a Valkey or Redis OSS (cluster mode enabled) shard or Valkey or Redis OSS (cluster mode disabled) replication group up to a maximum of five. You can do so using the AWS Management Console, the AWS CLI, or the ElastiCache API. **Topics** + [Using the AWS Management Console](#increase-replica-count-con) + [Using the AWS CLI](#increase-replica-count-cli) + [Using the ElastiCache API](#increase-replica-count-api) ## Using the AWS Management Console The following procedure uses the console to increase the number of replicas in a Valkey or Redis OSS (cluster mode enabled) replication group. **To increase the number of replicas in shards** 1. Sign in to the AWS Management Console and open the ElastiCache console at [ https://console.aws.amazon.com/elasticache/](https://console.aws.amazon.com/elasticache/). 1. In the navigation pane, choose **Valkey** or **Redis OSS**, and then choose the name of the replication group that you want to add replicas to. 1. Choose the box for each shard that you want to add replicas to. 1. Choose **Add replicas**. 1. Complete the **Add Replicas to Shards** page: + For **New number of replicas/shard**, enter the number of replicas that you want all of your selected shards to have. This value must be greater than or equal to **Current Number of Replicas per shard** and less than or equal to five. We recommend at least two replicas as a working minimum. + For **Availability Zones**, choose either **No preference** to have ElastiCache chose an Availability Zone for each new replica, or **Specify Availability Zones** to choose an Availability Zone for each new replica. If you choose **Specify Availability Zones**, for each new replica specify an Availability Zone using the list. 1. Choose **Add** to add the replicas or **Cancel** to cancel the operation. ## Using the AWS CLI To increase the number of replicas in a Valkey or Redis OSS shard, use the `increase-replica-count` command with the following parameters: + `--replication-group-id` – Required. Identifies which replication group you want to increase the number of replicas in. + `--apply-immediately` or `--no-apply-immediately` – Required. Specifies whether to increase the replica count immediately (`--apply-immediately`) or at the next maintenance window (`--no-apply-immediately`). Currently, `--no-apply-immediately` is not supported. + `--new-replica-count` – Optional. Specifies the number of replica nodes you want when finished, up to a maximum of five. Use this parameter for Valkey or Redis OSS (cluster mode disabled) replication groups where there is only one node group or Valkey or Redis OSS (cluster mode enabled) group, or where you want all node groups to have the same number of replicas. If this value is not larger than the current number of replicas in the node group, the call fails with an exception. + `--replica-configuration` – Optional. Allows you to set the number of replicas and Availability Zones for each node group independently. Use this parameter for Valkey or Redis OSS (cluster mode enabled) groups where you want to configure each node group independently. `--replica-configuration` has three optional members: + `NodeGroupId` – The four-digit ID for the node group that you are configuring. For Valkey or Redis OSS (cluster mode disabled) replication groups, the shard ID is always `0001`. To find a Valkey or Redis OSS (cluster mode enabled) node group's (shard's) ID, see [Finding a shard's ID](Shards.md#shard-find-id). + `NewReplicaCount` – The number of replicas that you want in this node group at the end of this operation. The value must be more than the current number of replicas, up to a maximum of five. If this value is not larger than the current number of replicas in the node group, the call fails with an exception. + `PreferredAvailabilityZones` – A list of `PreferredAvailabilityZone` strings that specify which Availability Zones the replication group's nodes are to be in. The number of `PreferredAvailabilityZone` values must equal the value of `NewReplicaCount` plus 1 to account for the primary node. If this member of `--replica-configuration` is omitted, ElastiCache for Redis OSS chooses the Availability Zone for each of the new replicas. **Important** You must include either the `--new-replica-count` or `--replica-configuration` parameter, but not both, in your call. **Example** The following example increases the number of replicas in the replication group `sample-repl-group` to three. When the example is finished, there are three replicas in each node group. This number applies whether this is a Valkey or Redis OSS (cluster mode disabled) group with a single node group or a Valkey or Redis OSS (cluster mode enabled) group with multiple node groups. For Linux, macOS, or Unix: ``` aws elasticache increase-replica-count \ --replication-group-id sample-repl-group \ --new-replica-count 3 \ --apply-immediately ``` For Windows: ``` aws elasticache increase-replica-count ^ --replication-group-id sample-repl-group ^ --new-replica-count 3 ^ --apply-immediately ``` The following example increases the number of replicas in the replication group `sample-repl-group` to the value specified for the two specified node groups. Given that there are multiple node groups, this is a Valkey or Redis OSS (cluster mode enabled) replication group. When specifying the optional `PreferredAvailabilityZones`, the number of Availability Zones listed must equal the value of `NewReplicaCount` plus 1 more. This approach accounts for the primary node for the group identified by `NodeGroupId`. For Linux, macOS, or Unix: ``` aws elasticache increase-replica-count \ --replication-group-id sample-repl-group \ --replica-configuration \ NodeGroupId=0001,NewReplicaCount=2,PreferredAvailabilityZones=us-east-1a,us-east-1c,us-east-1b \ NodeGroupId=0003,NewReplicaCount=3,PreferredAvailabilityZones=us-east-1a,us-east-1b,us-east-1c,us-east-1c \ --apply-immediately ``` For Windows: ``` aws elasticache increase-replica-count ^ --replication-group-id sample-repl-group ^ --replica-configuration ^ NodeGroupId=0001,NewReplicaCount=2,PreferredAvailabilityZones=us-east-1a,us-east-1c,us-east-1b ^ NodeGroupId=0003,NewReplicaCount=3,PreferredAvailabilityZones=us-east-1a,us-east-1b,us-east-1c,us-east-1c \ --apply-immediately ``` For more information about increasing the number of replicas using the CLI, see [increase-replica-count](https://docs.aws.amazon.com/cli/latest/reference/elasticache/increase-replica-count.html) in the *Amazon ElastiCache Command Line Reference.* ## Using the ElastiCache API To increase the number of replicas in a Valkey or Redis OSS shard, use the `IncreaseReplicaCount` action with the following parameters: + `ReplicationGroupId` – Required. Identifies which replication group you want to increase the number of replicas in. + `ApplyImmediately` – Required. Specifies whether to increase the replica count immediately (`ApplyImmediately=True`) or at the next maintenance window (`ApplyImmediately=False`). Currently, `ApplyImmediately=False` is not supported. + `NewReplicaCount` – Optional. Specifies the number of replica nodes you want when finished, up to a maximum of five. Use this parameter for Valkey or Redis OSS (cluster mode disabled) replication groups where there is only one node group, or Valkey or Redis OSS (cluster mode enabled) groups where you want all node groups to have the same number of replicas. If this value is not larger than the current number of replicas in the node group, the call fails with an exception. + `ReplicaConfiguration` – Optional. Allows you to set the number of replicas and Availability Zones for each node group independently. Use this parameter for Valkey or Redis OSS (cluster mode enabled) groups where you want to configure each node group independently. `ReplicaConfiguraion` has three optional members: + `NodeGroupId` – The four-digit ID for the node group you are configuring. For Valkey or Redis OSS (cluster mode disabled) replication groups, the node group (shard) ID is always `0001`. To find a Valkey or Redis OSS (cluster mode enabled) node group's (shard's) ID, see [Finding a shard's ID](Shards.md#shard-find-id). + `NewReplicaCount` – The number of replicas that you want in this node group at the end of this operation. The value must be more than the current number of replicas and a maximum of five. If this value is not larger than the current number of replicas in the node group, the call fails with an exception. + `PreferredAvailabilityZones` – A list of `PreferredAvailabilityZone` strings that specify which Availability Zones the replication group's nodes are to be in. The number of `PreferredAvailabilityZone` values must equal the value of `NewReplicaCount` plus 1 to account for the primary node. If this member of `ReplicaConfiguration` is omitted, ElastiCache for Redis OSS chooses the Availability Zone for each of the new replicas. **Important** You must include either the `NewReplicaCount` or `ReplicaConfiguration` parameter, but not both, in your call. **Example** The following example increases the number of replicas in the replication group `sample-repl-group` to three. When the example is finished, there are three replicas in each node group. This number applies whether this is a Valkey or Redis OSS (cluster mode disabled) group with a single node group, or a Valkey or Redis OSS (cluster mode enabled) group with multiple node groups. ``` https://elasticache.us-west-2.amazonaws.com/ ?Action=IncreaseReplicaCount &ApplyImmediately=True &NewReplicaCount=3 &ReplicationGroupId=sample-repl-group &Version=2015-02-02 &SignatureVersion=4 &SignatureMethod=HmacSHA256 &Timestamp=20150202T192317Z &X-Amz-Credential= ``` The following example increases the number of replicas in the replication group `sample-repl-group` to the value specified for the two specified node groups. Given that there are multiple node groups, this is a Valkey or Redis OSS (cluster mode enabled) replication group. When specifying the optional `PreferredAvailabilityZones`, the number of Availability Zones listed must equal the value of `NewReplicaCount` plus 1 more. This approach accounts for the primary node, for the group identified by `NodeGroupId`. ``` https://elasticache.us-west-2.amazonaws.com/ ?Action=IncreaseReplicaCount &ApplyImmediately=True &ReplicaConfiguration.ConfigureShard.1.NodeGroupId=0001 &ReplicaConfiguration.ConfigureShard.1.NewReplicaCount=2 &ReplicaConfiguration.ConfigureShard.1.PreferredAvailabilityZones.PreferredAvailabilityZone.1=us-east-1a &ReplicaConfiguration.ConfigureShard.1.PreferredAvailabilityZones.PreferredAvailabilityZone.2=us-east-1c &ReplicaConfiguration.ConfigureShard.1.PreferredAvailabilityZones.PreferredAvailabilityZone.3=us-east-1b &ReplicaConfiguration.ConfigureShard.2.NodeGroupId=0003 &ReplicaConfiguration.ConfigureShard.2.NewReplicaCount=3 &ReplicaConfiguration.ConfigureShard.2.PreferredAvailabilityZones.PreferredAvailabilityZone.1=us-east-1a &ReplicaConfiguration.ConfigureShard.2.PreferredAvailabilityZones.PreferredAvailabilityZone.2=us-east-1b &ReplicaConfiguration.ConfigureShard.2.PreferredAvailabilityZones.PreferredAvailabilityZone.3=us-east-1c &ReplicaConfiguration.ConfigureShard.2.PreferredAvailabilityZones.PreferredAvailabilityZone.4=us-east-1c &ReplicationGroupId=sample-repl-group &Version=2015-02-02 &SignatureVersion=4 &SignatureMethod=HmacSHA256 &Timestamp=20150202T192317Z &X-Amz-Credential= ``` For more information about increasing the number of replicas using the API, see [IncreaseReplicaCount](https://docs.aws.amazon.com/AmazonElastiCache/latest/APIReference/API_IncreaseReplicaCount.html) in the *Amazon ElastiCache API Reference.* # Decreasing the number of replicas in a shard You can decrease the number of replicas in a shard for Valkey or Redis OSS (cluster mode enabled), or in a replication group for Valkey or Redis OSS (cluster mode disabled): + For Valkey or Redis OSS (cluster mode disabled), you can decrease the number of replicas to one if Multi-AZ is enabled, and to zero if it isn't enabled. + For Valkey or Redis OSS (cluster mode enabled), you can decrease the number of replicas to zero. However, you can't fail over to a replica if your primary node fails. You can use the AWS Management Console, the AWS CLI or the ElastiCache API to decrease the number of replicas in a node group (shard) or replication group. **Topics** + [Using the AWS Management Console](#decrease-replica-count-con) + [Using the AWS CLI](#decrease-replica-count-cli) + [Using the ElastiCache API](#decrease-replica-count-api) ## Using the AWS Management Console The following procedure uses the console to decrease the number of replicas in a Valkey or Redis OSS (cluster mode enabled) replication group. **To decrease the number of replicas in a Valkey or Redis OSS shard** 1. Sign in to the AWS Management Console and open the ElastiCache console at [ https://console.aws.amazon.com/elasticache/](https://console.aws.amazon.com/elasticache/). 1. In the navigation pane, choose **Valkey** or **Redis OSS**, then choose the name of the replication group from which you want to delete replicas. 1. Choose the box for each shard you want to remove a replica node from. 1. Choose **Delete replicas**. 1. Complete the **Delete Replicas from Shards** page: 1. For **New number of replicas/shard**, enter the number of replicas that you want the selected shards to have. This number must be greater than or equal to 1. We recommend at least two replicas per shard as a working minimum. 1. Choose **Delete** to delete the replicas or **Cancel** to cancel the operation. **Important** If you don’t specify the replica nodes to be deleted, ElastiCache for Redis OSS automatically selects replica nodes for deletion. While doing so, ElastiCache for Redis OSS attempts to retain the Multi-AZ architecture for your replication group followed by retaining replicas with minimum replication lag with the primary. You can't delete the primary or primary nodes in a replication group. If you specify a primary node for deletion, the operation fails with an error event indicating that the primary node was selected for deletion. ## Using the AWS CLI To decrease the number of replicas in a Valkey or Redis OSS shard, use the `decrease-replica-count` command with the following parameters: + `--replication-group-id` – Required. Identifies which replication group you want to decrease the number of replicas in. + `--apply-immediately` or `--no-apply-immediately` – Required. Specifies whether to decrease the replica count immediately (`--apply-immediately`) or at the next maintenance window (`--no-apply-immediately`). Currently, `--no-apply-immediately` is not supported. + `--new-replica-count` – Optional. Specifies the number of replica nodes that you want. The value of `--new-replica-count` must be a valid value less than the current number of replicas in the node groups. For minimum permitted values, see [Decreasing the number of replicas in a shard](#decrease-replica-count). If the value of `--new-replica-count` doesn't meet this requirement, the call fails. + `--replicas-to-remove` – Optional. Contains a list of node IDs specifying the replica nodes to remove. + `--replica-configuration` – Optional. Allows you to set the number of replicas and Availability Zones for each node group independently. Use this parameter for Valkey or Redis OSS (cluster mode enabled) groups where you want to configure each node group independently. `--replica-configuration` has three optional members: + `NodeGroupId` – The four-digit ID for the node group that you are configuring. For Valkey or Redis OSS (cluster mode disabled) replication groups, the shard ID is always `0001`. To find a Valkey or Redis OSS (cluster mode enabled) node group's (shard's) ID, see [Finding a shard's ID](Shards.md#shard-find-id). + `NewReplicaCount` – An optional parameter that specifies the number of replica nodes you want. The value of `NewReplicaCount` must be a valid value less than the current number of replicas in the node groups. For minimum permitted values, see [Decreasing the number of replicas in a shard](#decrease-replica-count). If the value of `NewReplicaCount` doesn't meet this requirement, the call fails. + `PreferredAvailabilityZones` – A list of `PreferredAvailabilityZone` strings that specify which Availability Zones the replication group's nodes are in. The number of `PreferredAvailabilityZone` values must equal the value of `NewReplicaCount` plus 1 to account for the primary node. If this member of `--replica-configuration` is omitted, ElastiCache for Redis OSS chooses the Availability Zone for each of the new replicas. **Important** You must include one and only one of the `--new-replica-count`, `--replicas-to-remove`, or `--replica-configuration` parameters. **Example** The following example uses `--new-replica-count` to decrease the number of replicas in the replication group `sample-repl-group` to one. When the example is finished, there is one replica in each node group. This number applies whether this is a Valkey or Redis OSS (cluster mode disabled) group with a single node group or a Valkey or Redis OSS (cluster mode enabled) group with multiple node groups. For Linux, macOS, or Unix: ``` aws elasticache decrease-replica-count --replication-group-id sample-repl-group \ --new-replica-count 1 \ --apply-immediately ``` For Windows: ``` aws elasticache decrease-replica-count ^ --replication-group-id sample-repl-group ^ --new-replica-count 1 ^ --apply-immediately ``` The following example decreases the number of replicas in the replication group `sample-repl-group` by removing two specified replicas (`0001` and `0003`) from the node group. For Linux, macOS, or Unix: ``` aws elasticache decrease-replica-count \ --replication-group-id sample-repl-group \ --replicas-to-remove 0001,0003 \ --apply-immediately ``` For Windows: ``` aws elasticache decrease-replica-count ^ --replication-group-id sample-repl-group ^ --replicas-to-remove 0001,0003 \ --apply-immediately ``` The following example uses `--replica-configuration` to decrease the number of replicas in the replication group `sample-repl-group` to the value specified for the two specified node groups. Given that there are multiple node groups, this is a Valkey or Redis OSS (cluster mode enabled) replication group. When specifying the optional `PreferredAvailabilityZones`, the number of Availability Zones listed must equal the value of `NewReplicaCount` plus 1 more. This approach accounts for the primary node for the group identified by `NodeGroupId`. For Linux, macOS, or Unix: ``` aws elasticache decrease-replica-count \ --replication-group-id sample-repl-group \ --replica-configuration \ NodeGroupId=0001,NewReplicaCount=1,PreferredAvailabilityZones=us-east-1a,us-east-1c \ NodeGroupId=0003,NewReplicaCount=2,PreferredAvailabilityZones=us-east-1a,us-east-1b,us-east-1c \ --apply-immediately ``` For Windows: ``` aws elasticache decrease-replica-count ^ --replication-group-id sample-repl-group ^ --replica-configuration ^ NodeGroupId=0001,NewReplicaCount=2,PreferredAvailabilityZones=us-east-1a,us-east-1c ^ NodeGroupId=0003,NewReplicaCount=3,PreferredAvailabilityZones=us-east-1a,us-east-1b,us-east-1c \ --apply-immediately ``` For more information about decreasing the number of replicas using the CLI, see [decrease-replica-count](https://docs.aws.amazon.com/cli/latest/reference/elasticache/decrease-replica-count.html) in the *Amazon ElastiCache Command Line Reference.* ## Using the ElastiCache API To decrease the number of replicas in a Valkey or Redis OSS shard, use the `DecreaseReplicaCount` action with the following parameters: + `ReplicationGroupId` – Required. Identifies which replication group you want to decrease the number of replicas in. + `ApplyImmediately` – Required. Specifies whether to decrease the replica count immediately (`ApplyImmediately=True`) or at the next maintenance window (`ApplyImmediately=False`). Currently, `ApplyImmediately=False` is not supported. + `NewReplicaCount` – Optional. Specifies the number of replica nodes you want. The value of `NewReplicaCount` must be a valid value less than the current number of replicas in the node groups. For minimum permitted values, see [Decreasing the number of replicas in a shard](#decrease-replica-count). If the value of `--new-replica-count` doesn't meet this requirement, the call fails. + `ReplicasToRemove` – Optional. Contains a list of node IDs specifying the replica nodes to remove. + `ReplicaConfiguration` – Optional. Contains a list of node groups that allows you to set the number of replicas and Availability Zones for each node group independently. Use this parameter for Valkey or Redis OSS (cluster mode enabled) groups where you want to configure each node group independently. `ReplicaConfiguraion` has three optional members: + `NodeGroupId` – The four-digit ID for the node group you are configuring. For Valkey or Redis OSS (cluster mode disabled) replication groups, the node group ID is always `0001`. To find a Valkey or Redis OSS (cluster mode enabled) node group's (shard's) ID, see [Finding a shard's ID](Shards.md#shard-find-id). + `NewReplicaCount` – The number of replicas that you want in this node group at the end of this operation. The value must be less than the current number of replicas down to a minimum of 1 if Multi-AZ is enabled or 0 if Multi-AZ with Automatic Failover isn't enabled. If this value is not less than the current number of replicas in the node group, the call fails with an exception. + `PreferredAvailabilityZones` – A list of `PreferredAvailabilityZone` strings that specify which Availability Zones the replication group's nodes are in. The number of `PreferredAvailabilityZone` values must equal the value of `NewReplicaCount` plus 1 to account for the primary node. If this member of `ReplicaConfiguration` is omitted, ElastiCache for Redis OSS chooses the Availability Zone for each of the new replicas. **Important** You must include one and only one of the `NewReplicaCount`, `ReplicasToRemove`, or `ReplicaConfiguration` parameters. **Example** The following example uses `NewReplicaCount` to decrease the number of replicas in the replication group `sample-repl-group` to one. When the example is finished, there is one replica in each node group. This number applies whether this is a Valkey or Redis OSS (cluster mode disabled) group with a single node group or a Valkey or Redis OSS (cluster mode enabled) group with multiple node groups. ``` https://elasticache.us-west-2.amazonaws.com/ ?Action=DecreaseReplicaCount &ApplyImmediately=True &NewReplicaCount=1 &ReplicationGroupId=sample-repl-group &Version=2015-02-02 &SignatureVersion=4 &SignatureMethod=HmacSHA256 &Timestamp=20150202T192317Z &X-Amz-Credential= ``` The following example decreases the number of replicas in the replication group `sample-repl-group` by removing two specified replicas (`0001` and `0003`) from the node group. ``` https://elasticache.us-west-2.amazonaws.com/ ?Action=DecreaseReplicaCount &ApplyImmediately=True &ReplicasToRemove.ReplicaToRemove.1=0001 &ReplicasToRemove.ReplicaToRemove.2=0003 &ReplicationGroupId=sample-repl-group &Version=2015-02-02 &SignatureVersion=4 &SignatureMethod=HmacSHA256 &Timestamp=20150202T192317Z &X-Amz-Credential= ``` The following example uses `ReplicaConfiguration` to decrease the number of replicas in the replication group `sample-repl-group` to the value specified for the two specified node groups. Given that there are multiple node groups, this is a Valkey or Redis OSS (cluster mode enabled) replication group. When specifying the optional `PreferredAvailabilityZones`, the number of Availability Zones listed must equal the value of `NewReplicaCount` plus 1 more. This approach accounts for the primary node for the group identified by `NodeGroupId`. ``` https://elasticache.us-west-2.amazonaws.com/ ?Action=DecreaseReplicaCount &ApplyImmediately=True &ReplicaConfiguration.ConfigureShard.1.NodeGroupId=0001 &ReplicaConfiguration.ConfigureShard.1.NewReplicaCount=1 &ReplicaConfiguration.ConfigureShard.1.PreferredAvailabilityZones.PreferredAvailabilityZone.1=us-east-1a &ReplicaConfiguration.ConfigureShard.1.PreferredAvailabilityZones.PreferredAvailabilityZone.2=us-east-1c &ReplicaConfiguration.ConfigureShard.2.NodeGroupId=0003 &ReplicaConfiguration.ConfigureShard.2.NewReplicaCount=2 &ReplicaConfiguration.ConfigureShard.2.PreferredAvailabilityZones.PreferredAvailabilityZone.1=us-east-1a &ReplicaConfiguration.ConfigureShard.2.PreferredAvailabilityZones.PreferredAvailabilityZone.2=us-east-1b &ReplicaConfiguration.ConfigureShard.2.PreferredAvailabilityZones.PreferredAvailabilityZone.4=us-east-1c &ReplicationGroupId=sample-repl-group &Version=2015-02-02 &SignatureVersion=4 &SignatureMethod=HmacSHA256 &Timestamp=20150202T192317Z &X-Amz-Credential= ``` For more information about decreasing the number of replicas using the API, see [DecreaseReplicaCount](https://docs.aws.amazon.com/AmazonElastiCache/latest/APIReference/API_DecreaseReplicaCount.html) in the *Amazon ElastiCache API Reference.* # Adding a read replica for Valkey or Redis OSS (Cluster Mode Disabled) Information in the following topic applies to Valkey or Redis OSS (cluster mode disabled) replication groups only. As your read traffic increases, you might want to spread those reads across more nodes and reduce the read pressure on any one node. In this topic, you can find how to add a read replica to a Valkey or Redis OSS (cluster mode disabled) cluster. A Valkey or Redis OSS (cluster mode disabled) replication group can have a maximum of five read replicas. If you attempt to add a read replica to a replication group that already has five read replicas, the operation fails. For information about adding replicas to a Valkey or Redis OSS (cluster mode enabled) replication group, see the following: + [Scaling Valkey or Redis OSS (Cluster Mode Enabled) clusters](scaling-redis-cluster-mode-enabled.md) + [Increasing the number of replicas in a shard](increase-replica-count.md) You can add a read replica to a Valkey or Redis OSS (cluster mode disabled) cluster using the ElastiCache Console, the AWS CLI, or the ElastiCache API. **Related topics** + [Adding nodes to an ElastiCache cluster](Clusters.AddNode.md) + [Adding a read replica to a replication group (AWS CLI)](#Replication.AddReadReplica.CLI) + [Adding a read replica to a replication group using the API](#Replication.AddReadReplica.API) ## Adding a read replica to a replication group (AWS CLI) To add a read replica to a Valkey or Redis OSS (cluster mode disabled) replication group, use the AWS CLI `create-cache-cluster` command, with the parameter `--replication-group-id` to specify which replication group to add the cluster (node) to. The following example creates the cluster `my-read replica` and adds it to the replication group `my-replication-group`. The node types, parameter groups, security groups, maintenance window, and other settings for the read replica are the same as for the other nodes in `my-replication-group`. For Linux, macOS, or Unix: ``` aws elasticache create-cache-cluster \ --cache-cluster-id my-read-replica \ --replication-group-id my-replication-group ``` For Windows: ``` aws elasticache create-cache-cluster ^ --cache-cluster-id my-read-replica ^ --replication-group-id my-replication-group ``` For more information on adding a read replica using the CLI, see [create-cache-cluster](https://docs.aws.amazon.com/cli/latest/reference/elasticache/create-cache-cluster.html) in the *Amazon ElastiCache Command Line Reference.* ## Adding a read replica to a replication group using the API To add a read replica to a Valkey or Redis OSS (cluster mode disabled) replication group, use the ElastiCache `CreateCacheCluster` operation, with the parameter `ReplicationGroupId` to specify which replication group to add the cluster (node) to. The following example creates the cluster `myReadReplica` and adds it to the replication group `myReplicationGroup`. The node types, parameter groups, security groups, maintenance window, and other settings for the read replica are the same as for the other nodes `myReplicationGroup`. ``` https://elasticache.us-west-2.amazonaws.com/ ?Action=CreateCacheCluster &CacheClusterId=myReadReplica &ReplicationGroupId=myReplicationGroup &Version=2015-02-02 &SignatureVersion=4 &SignatureMethod=HmacSHA256 &Timestamp=20150202T192317Z &X-Amz-Credential= ``` For more information on adding a read replica using the API, see [CreateCacheCluster](https://docs.aws.amazon.com/AmazonElastiCache/latest/APIReference/API_CreateCacheCluster.html) in the *Amazon ElastiCache API Reference.* # Deleting a read replica for Valkey or Redis OSS (Cluster Mode Disabled) Information in the following topic applies to Valkey or Redis OSS (cluster mode disabled) replication groups only. As read traffic on your Valkey or Redis OSS replication group changes, you might want to add or remove read replicas. Removing a node from a replication group is the same as just deleting a cluster, though there are restrictions: + You cannot remove the primary from a replication group. If you want to delete the primary, do the following: 1. Promote a read replica to primary. For more information on promoting a read replica to primary, see [Promoting a read replica to primary, for Valkey or Redis OSS (cluster mode disabled) replication groups](Replication.PromoteReplica.md). 1. Delete the old primary. For a restriction on this method, see the next point. + If Multi-AZ is enabled on a replication group, you can't remove the last read replica from the replication group. In this case, do the following: 1. Modify the replication group by disabling Multi-AZ. For more information, see [Modifying a replication group](Replication.Modify.md). 1. Delete the read replica. You can remove a read replica from a Valkey or Redis OSS (cluster mode disabled) replication group using the ElastiCache console, the AWS CLI for ElastiCache, or the ElastiCache API. For directions on deleting a cluster from a Valkey or Redis OSS replication group, see the following: + [Using the AWS Management Console](Clusters.Delete.md#Clusters.Delete.CON) + [Using the AWS CLI to delete an ElastiCache cluster](Clusters.Delete.md#Clusters.Delete.CLI) + [Using the ElastiCache API](Clusters.Delete.md#Clusters.Delete.API) + [Scaling Valkey or Redis OSS (Cluster Mode Enabled) clusters](scaling-redis-cluster-mode-enabled.md) + [Decreasing the number of replicas in a shard](decrease-replica-count.md)