Overview

• Redis cluster allows you to deploy fully managed Redis database cluster. You don't have to worry about capacity scaling, hardware & VM provisioning, cluster setup, patching or backups.

• Redis is a fast, NoSQL in-memory data store that can provide sub-millisecond latency.

• Clusters are easy to set up, built on open-source Redis and compatible with the Redis APIs - ElastiCache for Redis works with your Redis clients and uses the open Redis data format to store your data.

• It is often used as a cache to offload main database systems.

Under the hood

Redis clusters are fully managed (powered by Amazon ElastiCache for Redis).

Multiple topologies are possible for the deployment: from a one node database, to a multi-node sharded cluster. See section Cluster topology for more info.

When to use

Redis is used in cases when the performance is important. Example use-cases include caching, chat apps, messaging, queues, real-time analytics, etc.

Advantages

• Performance - Redis is an in-memory data store and can deliver sub-millisecond response times. In comparison to disk-based databases (where most operations need a roundtrip to a disk), in-memory data stores can be an order of magnitude faster.
• Fully managed - You don't have to worry about capacity scaling, hardware & VM provisioning, cluster setup, sharding process, patching, backups, etc.
• High availability - Redis supports both clustered and non-clustered modes and provides high availability via support for automatic failovers with minimal impact.

Disadvantages

• Data persistence - Redis offers 2 options for persistency: regular snap-shotting and append-only files. None of them is as secure as a real transactional server providing undo/redo logging, point-in-time recovery, etc.
• Hard to store large amounts of data - All your data must fit in memory.
• Requires topology-aware clients - Clients connecting to the Redis cluster should be aware of the cluster topology. This requires more configuration on the client.

Basic usage

• Following example shows basic usage of redis-cluster resource. Only required properties are instanceSize and defaultUserPassword.
• The example shows a single node redis-cluster.

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resources:
  myRedisCluster:
    type: redis-cluster
    properties:
      instanceSize: cache.t3.micro
      defaultUserPassword: $Secret('redis.password')

  myFunction:
    type: function
    properties:
      packaging:
        type: stacktape-lambda-buildpack
        properties:
          entryfilePath: path/to/my/lambda.ts
      environment:
        - name: REDIS_HOST
          value: $ResourceParam('redisCluster', 'host')
        - name: REDIS_PORT
          value: $ResourceParam('redisCluster', 'port')
        - name: REDIS_PASSWORD
          value: $This().resources.myRedisCluster.properties.defaultUserPassword

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import { Cluster } from 'ioredis';

const redisClient = new Redis({
  host: process.env.REDIS_HOST,
  port: Number(process.env.REDIS_PORT),
  password: process.env.REDIS_PASSWORD
});

const handler = async (event, context) => {
  await redisClient.set('currentTime', `${Date.now()}`);

  const value = await redisClient.get('currentTime');

  return { result: value };
};

export default handler;

Node instance size

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resources:
  myRedisCluster:
    type: redis-cluster
    properties:
      instanceSize: cache.t3.micro
      defaultUserPassword: $Secret('redis.password')

Default user password

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resources:
  myRedisCluster:
    type: redis-cluster
    properties:
      instanceSize: cache.t3.micro
      defaultUserPassword: $Secret('redis.password')

Cluster topology

• Cluster topology is based on the amount of replica nodes and the amount of shards.
• Performance and high-availability of the cluster are dependent on the topology.

Single node (non-sharded) cluster

• Single node, non-sharded cluster has only one node. It's not highly available.

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resources:
  myRedisCluster:
    type: redis-cluster
    properties:
      instanceSize: cache.t3.micro
      defaultUserPassword: $Secret('redis.password')

Multi node (non-sharded) cluster

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resources:
  myRedisCluster:
    type: redis-cluster
    properties:
      instanceSize: cache.t3.micro
      defaultUserPassword: $Secret('redis.password')
      numReplicaNodes: 2

Sharded cluster

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resources:
  myRedisCluster:
    type: redis-cluster
    properties:
      instanceSize: cache.t3.micro
      defaultUserPassword: $Secret('redis.password')
      enableSharding: true
      numShards: 2
      numReplicaNodes: 2

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import { Cluster } from 'ioredis';

const redisClusterClient = new Cluster(
  [
    {
      host: process.env.REDIS_HOST,
      port: Number(process.env.REDIS_PORT)
    }
  ],
  {
    redisOptions: { tls: {}, password: process.env.REDIS_PASSWORD },
    dnsLookup: (address, callback) => callback(null, address)
  }
);

const handler = async (event, context) => {
  await redisClusterClient.set('currentTime', `${Date.now()}`);

  const value = await redisClusterClient.get('currentTime');

  return { result: value };
};

export default handler;

Logging

• When logging is enabled, slow-log will be sent to a pre-created Cloudwatch log group.

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resources:
  myRedisCluster:
    type: redis-cluster
    properties:
      instanceSize: cache.t3.micro
      defaultUserPassword: $Secret('redis.password')
      logging:
        format: json

Forwarding logs

It is possible to forward logs to the third party services/databases. See page Forwarding logs for more information and examples.

Accessibility

• You can configure which resources and hosts can access your cluster.
• Redis clusters do not support public IP addresses. Therefore, only 2 access modes are supported.

VPC mode

• The cluster can be accessed only from resources within the default VPC.
• Any function (provided it has joinDefaultVpc set to true), batch job or container workload or service within your stack can access the cluster.

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resources:
  myRedisCluster:
    type: redis-cluster
    properties:
      instanceSize: cache.t3.micro
      defaultUserPassword: $Secret('redis.password')
      accessibility:
        accessibilityMode: vpc

Scoping workloads in VPC mode

• Similar to vpc mode, but even more restrictive. In addition to resource being in the VPC, any host or resource trying to access your cluster must explicitly include the cluster in its connectTo list.

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resources:
  myRedisCluster:
    type: redis-cluster
    properties:
      instanceSize: cache.t3.micro
      defaultUserPassword: $Secret('redis.password')
      accessibility:
        accessibilityMode: scoping-workloads-in-vpc

Referenceable parameters

Pricing

You are charged for:

• Computing nodes, shards and replica nodes:
  • Price depends on the instance size, number of shards and number of replica nodes.
  • Can be calculated as number of shards * (number of replica nodes + 1 (there is always primary)) * price for node instance
  • EXAMPLE 1: Cheapest non-sharded cluster using cache.t3.micro instance with 0 replicaNodes: 1 * (0+1) * $0.017 = $0.017/hour (~$12.50/month)
  • EXAMPLE 2: Sharded cluster with 2 shards using cache.t3.micro and 1 replicaNode: 2 * (1+1) * $0.017 = $0.068 per hour (~$49/month)
• Data transfer:
  • In most cases there should be no additional cost.
• Backups:
  • If retained for at most 1 day: free
  • $0.085/GB/month after that

Free Tier (eligible for first 12 months)

• Includes 750 hours of t2.micro instances (t3.micro for the regions in which t2.micro is not available) each month.

To learn more about pricing, refer to AWS pricing page

API Reference