# Rack-zone awareness in Redis Enterprise Software ```json metadata { "schema_version": 2, "title": "Rack-zone awareness in Redis Enterprise Software", "description": "Rack-zone awareness ensures high availability in the event of a rack or zone failure.", "categories": ["docs","operate","rs","kubernetes"], "tableOfContents": {"sections":[{"id":"rack-zone-id-rules","title":"Rack-zone ID rules"},{"id":"node-layout-guidelines","title":"Node layout guidelines"},{"children":[{"id":"new-cluster","title":"New cluster"},{"id":"existing-cluster","title":"Existing cluster"}],"id":"set-up-rack-zone-awareness","title":"Set up rack-zone awareness"},{"children":[{"id":"rearrange-database-shards","title":"Rearrange database shards"}],"id":"enable-database-rack-zone-awareness","title":"Enable database rack-zone awareness"},{"id":"shard-placement-without-rack-zone-awareness","title":"Shard placement without rack-zone awareness"}]} , "codeExamples": [] } ``` Rack-zone awareness helps ensure high availability in the event of a rack or zone failure. When you enable rack-zone awareness in a Redis Enterprise Software cluster, you assign a [rack-zone ID](#rack-zone-id-rules) to each node. This ID is used to map the node to a physical rack or logical zone. The cluster can then ensure that master shards, corresponding replica shards, and associated endpoints are placed on [nodes in different racks or zones](#node-layout-guidelines). In the event of a rack or zone failure, the replicas and endpoints in the remaining racks and zones are promoted. This ensures high availability when a rack or zone fails. There is no limitation on the number of racks and zones per cluster. Each node can belong to a different rack or multiple nodes can belong to the same rack. Rack-zone awareness affects various cluster, node, and database actions, such as node rebalancing, node removal, node replacement, shard and endpoint migration, and database failover. ## Rack-zone ID rules The rack-zone ID must comply with the following rules: - Maximum length of 63 characters. - Characters consist of letters, digits, and hyphens ('-'). Underscores ('_') are also accepted as of Redis Enterprise Software 6.4.2-61. - ID starts with a letter and ends with a letter or a digit. > [!NOTE] > Rack-zone IDs are **case-insensitive** (uppercase and lowercase letter are treated as the same). ## Node layout guidelines Avoid placing the majority of nodes in one availability zone. If a Redis Enterprise Software cluster consists of three nodes (the recommended minimum), follow these guidelines: - For high availability, the three nodes must be distributed across three *distinct* racks or zones. - When using availability zones, all three zones should exist within the same *region* to avoid potential latency issues. ## Set up rack-zone awareness To enable rack-zone awareness, you need to configure it for the cluster, nodes, and [databases](#enable-database-rack-zone-awareness). > [!NOTE] > - After rack-zone awareness is enabled for a cluster, it cannot be turned off. > > - After a rack ID is assigned to a node, it cannot be changed. ### New cluster You can set up rack-zone awareness for the cluster and its nodes during [cluster creation](https://redis.io/docs/latest/operate/rs/clusters/new-cluster-setup): 1. In the **Cluster** screen's **Configuration** section, enable **Rack zone awareness**. 1. Select **Next** to continue to the **Node** configuration screen. 1. Enter a **Rack-zone ID** for the current node. 1. Finish [cluster setup](https://redis.io/docs/latest/operate/rs/clusters/new-cluster-setup). 1. For every [node you add to the cluster](https://redis.io/docs/latest/operate/rs/clusters/add-node), assign a different **Rack-zone ID**. ### Existing cluster If you did not configure rack-zone awareness during cluster creation, you can configure rack-zone awareness for existing clusters using the [REST API](https://redis.io/docs/latest/operate/rs/references/rest-api): 1. For each node in the cluster, assign a different rack-zone ID using the REST API to [update the node](https://redis.io/docs/latest/operate/rs/references/rest-api/requests/nodes#put-node): ```sh PUT /v1/nodes/ { "rack_id": "rack-zone-ID" } ``` 1. [Update the cluster policy](https://redis.io/docs/latest/operate/rs/references/rest-api/requests/cluster/policy#put-cluster-policy) to enable rack-zone awareness: ```sh PUT /v1/cluster/policy { "rack_aware": true } ``` ## Enable database rack-zone awareness Before you can enable rack-zone awareness for a database, you must configure rack-zone awareness for the cluster and its nodes. For more information, see [set up rack-zone awareness](#set-up-rack-zone-awareness). To enable rack-zone awareness for a database, use a [REST API request](https://redis.io/docs/latest/operate/rs/references/rest-api/requests/bdbs#put-bdbs): ```sh PUT /v1/bdbs/ { "rack_aware": true } ``` ### Rearrange database shards After you enable rack-zone awareness for an existing database, you should generate an optimized shard placement blueprint using the [REST API](https://redis.io/docs/latest/operate/rs/references/rest-api) and use it to rearrange the shards in different racks or zones. 1. [Generate an optimized shard placement blueprint](https://redis.io/docs/latest/operate/rs/references/rest-api/requests/bdbs/actions/optimize_shards_placement#get-bdbs-actions-optimize-shards-placement): 1. Send the following `GET` request: ```sh GET /v1/bdbs//actions/optimize_shards_placement ``` 1. Copy the `cluster-state-id` from the response headers. 1. Copy the JSON response body, which represents the new shard placement blueprint. 1. [Rearrange the database shards](https://redis.io/docs/latest/operate/rs/references/rest-api/requests/bdbs/actions/optimize_shards_placement#put-bdbs-rearrange-shards) according to the new shard placement blueprint: 1. In the request headers, include the `cluster-state-id` from the `optimize_shards_placement` response. 1. Add the following JSON in the request body and replace `` with the new blueprint: ```sh { "shards_blueprint": } ``` 1. Send the following `PUT` request to rearrange the shards: ```sh PUT /v1/bdbs/ ``` ## Shard placement without rack-zone awareness Even if a database has rack-zone awareness turned off, the cluster still ensures that master and replica shards are placed on distinct nodes.