# Online resharding for MemoryDB
By using online resharding and with MemoryDB, you can scale your MemoryDB dynamically with no downtime. This approach means that your cluster can continue to serve requests even while scaling or rebalancing is in process.
You can do the following:
+ **Scale out** – Increase read and write capacity by adding shards to your MemoryDB cluster.
If you add one or more shards to your cluster, the number of nodes in each new shard is the same as the number of nodes in the smallest of the existing shards.
+ **Scale in** – Reduce read and write capacity, and thereby costs, by removing shards from your MemoryDB cluster.
Currently, the following limitations apply to MemoryDB online resharding:
+ There are limitations with slots or keyspaces and large items:
If any of the keys in a shard contain a large item, that key isn't migrated to a new shard when scaling out . This functionality can result in unbalanced shards.
If any of the keys in a shard contain a large item (items greater than 256 MB after serialization), that shard isn't deleted when scaling in. This functionality can result in some shards not being deleted.
+ When scaling out, the number of nodes in any new shards equals the number of nodes in the existing shards.
For more information, see [Best practices: Online cluster resizing](best-practices-online-resharding.md).
You can horizontally scale your MemoryDB clusters using the AWS Management Console, the AWS CLI, and the MemoryDB API.
## Adding shards with online resharding
You can add shards to your MemoryDB cluster using the AWS Management Console, AWS CLI, or MemoryDB API.
### Adding shards (Console)
You can use the AWS Management Console to add one or more shards to your MemoryDB cluster. The following procedure describes the process.
****
1. Sign in to the AWS Management Console and open the MemoryDB console at [https://console.aws.amazon.com/memorydb/](https://console.aws.amazon.com/memorydb/).
1. From the list of clusters, choose the cluster name from which you want to add a shard.
1. Under the **Shards and nodes** tab, choose **Add/Delete shards**
1. In **New number of shards**, enter the the number of shards you want.
1. Choose **Confirm** to keep the changes or **Cancel** to discard.
### Adding shards (AWS CLI)
The following process describes how to reconfigure the shards in your MemoryDB cluster by adding shards using the AWS CLI.
Use the following parameters with `update-cluster`.
**Parameters**
+ `--cluster-name` – Required. Specifies which cluster (cluster) the shard reconfiguration operation is to be performed on.
+ `--shard-configuration` – Required. Allows you to set the number of shards.
+ `ShardCount` – Set this property to specify the number of shards you want.
**Example**
The following example modifies the number of shards in the cluster `my-cluster` to 2.
For Linux, macOS, or Unix:
```
aws memorydb update-cluster \
--cluster-name my-cluster \
--shard-configuration \
ShardCount=2
```
For Windows:
```
aws memorydb update-cluster ^
--cluster-name my-cluster ^
--shard-configuration ^
ShardCount=2
```
It returns the following JSON response:
```
{
"Cluster": {
"Name": "my-cluster",
"Status": "updating",
"NumberOfShards": 2,
"AvailabilityMode": "MultiAZ",
"ClusterEndpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
},
"NodeType": "db.r6g.large",
"EngineVersion": "6.2",
"EnginePatchVersion": "6.2.6",
"ParameterGroupName": "default.memorydb-redis6",
"ParameterGroupStatus": "in-sync",
"SubnetGroupName": "my-sg",
"TLSEnabled": true,
"ARN": "arn:aws:memorydb:us-east-1:xxxxxxexamplearn:cluster/my-cluster",
"SnapshotRetentionLimit": 0,
"MaintenanceWindow": "wed:03:00-wed:04:00",
"SnapshotWindow": "04:30-05:30",
"DataTiering": "false",
"AutoMinorVersionUpgrade": true
}
}
```
To view the details of the updated cluster once its status changes from *updating* to *available*, use the following command:
For Linux, macOS, or Unix:
```
aws memorydb describe-clusters \
--cluster-name my-cluster
--show-shard-details
```
For Windows:
```
aws memorydb describe-clusters ^
--cluster-name my-cluster
--show-shard-details
```
It will return the following JSON response:
```
{
"Clusters": [
{
"Name": "my-cluster",
"Status": "available",
"NumberOfShards": 2,
"Shards": [
{
"Name": "0001",
"Status": "available",
"Slots": "0-8191",
"Nodes": [
{
"Name": "my-cluster-0001-001",
"Status": "available",
"AvailabilityZone": "us-east-1a",
"CreateTime": "2021-08-21T20:22:12.405000-07:00",
"Endpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
}
},
{
"Name": "my-cluster-0001-002",
"Status": "available",
"AvailabilityZone": "us-east-1b",
"CreateTime": "2021-08-21T20:22:12.405000-07:00",
"Endpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
}
}
],
"NumberOfNodes": 2
},
{
"Name": "0002",
"Status": "available",
"Slots": "8192-16383",
"Nodes": [
{
"Name": "my-cluster-0002-001",
"Status": "available",
"AvailabilityZone": "us-east-1b",
"CreateTime": "2021-08-22T14:26:18.693000-07:00",
"Endpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
}
},
{
"Name": "my-cluster-0002-002",
"Status": "available",
"AvailabilityZone": "us-east-1a",
"CreateTime": "2021-08-22T14:26:18.765000-07:00",
"Endpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
}
}
],
"NumberOfNodes": 2
}
],
"ClusterEndpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
},
"NodeType": "db.r6g.large",
"EngineVersion": "6.2",
"EnginePatchVersion": "6.2.6",
"ParameterGroupName": "default.memorydb-redis6",
"ParameterGroupStatus": "in-sync",
"SubnetGroupName": "my-sg",
"TLSEnabled": true,
"ARN": "arn:aws:memorydb:us-east-1:xxxxxxexamplearn:cluster/my-cluster",
"SnapshotRetentionLimit": 0,
"MaintenanceWindow": "wed:03:00-wed:04:00",
"SnapshotWindow": "04:30-05:30",
"ACLName": "my-acl",
"DataTiering": "false",
"AutoMinorVersionUpgrade": true
}
]
}
```
For more information, see [update-cluster](https://docs.aws.amazon.com/cli/latest/reference/memorydb/update-cluster.html) in the AWS CLI Command Reference.
### Adding shards (MemoryDB API)
You can use the MemoryDB API to reconfigure the shards in your MemoryDB cluster online by using the `UpdateCluster` operation.
Use the following parameters with `UpdateCluster`.
**Parameters**
+ `ClusterName` – Required. Specifies which cluster the shard reconfiguration operation is to be performed on.
+ `ShardConfiguration` – Required. Allows you to set the number of shards.
+ `ShardCount` – Set this property to specify the number of shards you want.
For more information, see [UpdateCluster](https://docs.aws.amazon.com/memorydb/latest/APIReference/API_UpdateCluster.html).
## Removing shards with online resharding
You can remove shards from your MemoryDB cluster using the AWS Management Console, AWS CLI, or MemoryDB API.
### Removing shards (Console)
The following process describes how to reconfigure the shards in your MemoryDB cluster by removing shards using the AWS Management Console.
**Important**
Before removing shards from your cluster, MemoryDB makes sure that all your data will fit in the remaining shards. If the data will fit, shards are deleted from the cluster as requested. If the data won't fit in the remaining shards, the process is terminated and the cluster is left with the same shard configuration as before the request was made.
You can use the AWS Management Console to remove one or more shards from your MemoryDB cluster. You cannot remove all the shards in a cluster. Instead, you must delete the cluster. For more information, see [Step 5: Deleting a cluster](getting-started.md#clusters.delete). The following procedure describes the process for removing one or more shards.
****
1. Sign in to the AWS Management Console and open the MemoryDB console at [https://console.aws.amazon.com/memorydb/](https://console.aws.amazon.com/memorydb/).
1. From the list of clusters, choose the cluster name from which you want to remove a shard.
1. Under the **Shards and nodes** tab, choose **Add/Delete shards**
1. In **New number of shards**, enter the the number of shards you want (with a minimum of 1).
1. Choose **Confirm** to keep the changes or **Cancel** to discard.
### Removing shards (AWS CLI)
The following process describes how to reconfigure the shards in your MemoryDB cluster by removing shards using the AWS CLI.
**Important**
Before removing shards from your cluster, MemoryDB makes sure that all your data will fit in the remaining shards. If the data will fit, shards are deleted from the cluster as requested and their keyspaces mapped into the remaining shards. If the data will not fit in the remaining shards, the process is terminated and the cluster is left with the same shard configuration as before the request was made.
You can use the AWS CLI to remove one or more shards from your MemoryDB cluster. You cannot remove all the shards in a cluster. Instead, you must delete the cluster. For more information, see [Step 5: Deleting a cluster](getting-started.md#clusters.delete).
Use the following parameters with `update-cluster`.
**Parameters**
+ `--cluster-name` – Required. Specifies which cluster (cluster) the shard reconfiguration operation is to be performed on.
+ `--shard-configuration` – Required. Allows you to set the number of shards using the `ShardCount` property:
`ShardCount` – Set this property to specify the number of shards you want.
**Example**
The following example modifies the number of shards in the cluster `my-cluster` to 2.
For Linux, macOS, or Unix:
```
aws memorydb update-cluster \
--cluster-name my-cluster \
--shard-configuration \
ShardCount=2
```
For Windows:
```
aws memorydb update-cluster ^
--cluster-name my-cluster ^
--shard-configuration ^
ShardCount=2
```
It returns the following JSON response:
```
{
"Cluster": {
"Name": "my-cluster",
"Status": "updating",
"NumberOfShards": 2,
"AvailabilityMode": "MultiAZ",
"ClusterEndpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
},
"NodeType": "db.r6g.large",
"EngineVersion": "6.2",
"EnginePatchVersion": "6.2.6",
"ParameterGroupName": "default.memorydb-redis6",
"ParameterGroupStatus": "in-sync",
"SubnetGroupName": "my-sg",
"TLSEnabled": true,
"ARN": "arn:aws:memorydb:us-east-1:xxxxxxexamplearn:cluster/my-cluster",
"SnapshotRetentionLimit": 0,
"MaintenanceWindow": "wed:03:00-wed:04:00",
"SnapshotWindow": "04:30-05:30",
"DataTiering": "false",
"AutoMinorVersionUpgrade": true
}
}
```
To view the details of the updated cluster once its status changes from *updating* to *available*, use the following command:
For Linux, macOS, or Unix:
```
aws memorydb describe-clusters \
--cluster-name my-cluster
--show-shard-details
```
For Windows:
```
aws memorydb describe-clusters ^
--cluster-name my-cluster
--show-shard-details
```
It will return the following JSON response:
```
{
"Clusters": [
{
"Name": "my-cluster",
"Status": "available",
"NumberOfShards": 2,
"Shards": [
{
"Name": "0001",
"Status": "available",
"Slots": "0-8191",
"Nodes": [
{
"Name": "my-cluster-0001-001",
"Status": "available",
"AvailabilityZone": "us-east-1a",
"CreateTime": "2021-08-21T20:22:12.405000-07:00",
"Endpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
}
},
{
"Name": "my-cluster-0001-002",
"Status": "available",
"AvailabilityZone": "us-east-1b",
"CreateTime": "2021-08-21T20:22:12.405000-07:00",
"Endpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
}
}
],
"NumberOfNodes": 2
},
{
"Name": "0002",
"Status": "available",
"Slots": "8192-16383",
"Nodes": [
{
"Name": "my-cluster-0002-001",
"Status": "available",
"AvailabilityZone": "us-east-1b",
"CreateTime": "2021-08-22T14:26:18.693000-07:00",
"Endpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
}
},
{
"Name": "my-cluster-0002-002",
"Status": "available",
"AvailabilityZone": "us-east-1a",
"CreateTime": "2021-08-22T14:26:18.765000-07:00",
"Endpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
}
}
],
"NumberOfNodes": 2
}
],
"ClusterEndpoint": {
"Address": "clustercfg.my-cluster.xxxxxx.memorydb.us-east-1.amazonaws.com",
"Port": 6379
},
"NodeType": "db.r6g.large",
"EngineVersion": "6.2",
"EnginePatchVersion": "6.2.6",
"ParameterGroupName": "default.memorydb-redis6",
"ParameterGroupStatus": "in-sync",
"SubnetGroupName": "my-sg",
"TLSEnabled": true,
"ARN": "arn:aws:memorydb:us-east-1:xxxxxxexamplearn:cluster/my-cluster",
"SnapshotRetentionLimit": 0,
"MaintenanceWindow": "wed:03:00-wed:04:00",
"SnapshotWindow": "04:30-05:30",
"ACLName": "my-acl",
"DataTiering": "false",
"AutoMinorVersionUpgrade": true
}
]
}
```
For more information, see [update-cluster](https://docs.aws.amazon.com/cli/latest/reference/memorydb/update-cluster.html) in the AWS CLI Command Reference.
### Removing shards (MemoryDB API)
You can use the MemoryDB API to reconfigure the shards in your MemoryDB cluster online by using the `UpdateCluster` operation.
The following process describes how to reconfigure the shards in your MemoryDB cluster by removing shards using the MemoryDB API.
**Important**
Before removing shards rom your cluster, MemoryDB makes sure that all your data will fit in the remaining shards. If the data will fit, shards are deleted from the cluster as requested and their keyspaces mapped into the remaining shards. If the data will not fit in the remaining shards, the process is terminated and the cluster is left with the same shard configuration as before the request was made.
You can use the MemoryDB API to remove one or more shards from your MemoryDB cluster. You cannot remove all the shards in a cluster. Instead, you must delete the cluster. For more information, see [Step 5: Deleting a cluster](getting-started.md#clusters.delete).
Use the following parameters with `UpdateCluster`.
**Parameters**
+ `ClusterName` – Required. Specifies which cluster (cluster) the shard reconfiguration operation is to be performed on.
+ `ShardConfiguration` – Required. Allows you to set the number of shards using the `ShardCount` property:
`ShardCount` – Set this property to specify the number of shards you want.