Akka.Persistence.Redis

Akka Persistence Redis Plugin is a plugin for Akka persistence that provides several components:

• a journal store and
• a snapshot store.

NOTE: in Akka.Persistence.Redis v1.4.16 we removed Akka.Persistence.Query support. Please read more about that decision and comment here: https://github.com/akkadotnet/Akka.Persistence.Redis/issues/126

This plugin stores data in a redis database and based on Stackexchange.Redis library.

Installation

From Nuget Package Manager

Install-Package Akka.Persistence.Redis

From .NET CLI

dotnet add package Akka.Persistence.Redis

Journal

To activate the journal plugin, add the following line to your HOCON config:

akka.persistence.journal.plugin = "akka.persistence.journal.redis"

This will run the journal with its default settings. The default settings can be changed with the configuration properties defined in your HOCON config:

akka.persistence.journal.redis {
  # qualified type name of the Redis persistence journal actor
  class = "Akka.Persistence.Redis.Journal.RedisJournal, Akka.Persistence.Redis"

  # connection string, as described here: https://stackexchange.github.io/StackExchange.Redis/Configuration#basic-configuration-strings
  configuration-string = ""

  # Redis journals key prefixes. Leave it for default or change it to appropriate value. WARNING: don't change it on production instances.
  key-prefix = ""
}  

Configuration

• configuration-string - connection string, as described here: https://stackexchange.github.io/StackExchange.Redis/Configuration#basic-configuration-strings
• key-prefix - Redis journals key prefixes. Leave it for default or change it to customized value. WARNING: don't change this value after you've started persisting data in production.
• database - Set the Redis default database to use. If you added defaultDatabase to the connection-strings, you have to set database to the value of defaultDatabase.
• use-database-number-from-connection-string - determines redis database precedence when a user adds defaultDatabase to the connection-strings. For Redis Cluster, the defaultDatabase is 0! See below:

NOTE: Redis Standalone supports deploying multiple instances, but Redis cluster does not. The default database with Redis Cluster is always 0 - If you are deploying Redis Cluster, you don't need to add the defaultDatabase to the connection-string'! cluster-spec

Snapshot Store

To activate the snapshot plugin, add the following line to your HOCON config:

akka.persistence.snapshot-store.plugin = "akka.persistence.snapshot-store.redis"

This will run the snapshot-store with its default settings. The default settings can be changed with the configuration properties defined in your HOCON config:

akka.persistence.snapshot-store.redis {
  # qualified type name of the Redis persistence journal actor
  class = "Akka.Persistence.Redis.Snapshot.RedisSnapshotStore, Akka.Persistence.Redis"

  # connection string, as described here: https://stackexchange.github.io/StackExchange.Redis/Configuration#basic-configuration-strings
  configuration-string = ""

  # Redis journals key prefixes. Leave it for default or change it to appropriate value. WARNING: don't change it on production instances.
  key-prefix = ""
}  

Configuration

• configuration-string - connection string, as described here: https://stackexchange.github.io/StackExchange.Redis/Configuration#basic-configuration-strings
• key-prefix - Redis journals key prefixes. Leave it for default or change it to appropriate value. WARNING: don't change it on production instances.

Security and Access Control

You can secure the Redis server Akka.Persistence.Redis connects to by leveraging Redis ACL and requiring users to use AUTH to connect to the Redis server.

1. Redis ACL You can use Redis ACL to:

• Create users
• Set user passwords
• Limit the set of Redis commands a user can use
• Allow/disallow pub/sub channels
• Allow/disallow certain keys
• etc.

2. Redis SSL/TLS You can use redis-cli to enable SSL/TLS feature in Redis.

3. StackExchange.Redis Connection string To connect to ACL enabled Redis server, you will need to set the user and password option in the connection string: "myServer.net:6380,user=<username>,password=<password>"

All of these features are supported via StackExchange.Redis, which Akka.Persistence.Redis uses internally, and you only need to customize your akka.persistence.journal.redis.configuration-string and akka.persistence.snapshot-store.redis.configuration-string values to customize it.

Enabling TLS

For instance, if you want to enable TLS on your Akka.Persistence.Redis instance:

akka.persistence.journal.redis.configuration-string = "contoso5.redis.cache.windows.net,ssl=true,password=..."

Or if you need to connect to multiple redis instances in a cluster:

akka.persistence.journal.redis.configuration-string = "contoso5.redis.cache.windows.net, contoso4.redis.cache.windows.net,ssl=true,password=..."

Enabling ACL

To connect to your redis instance with access control (ACL) support for Akka.Persistence.Redis, all you need to do is specify the user name and password in your connection string and this will restrict the StackExchange.Redis client used internally by Akka.Persistence.Redis to whatever permissions you specified in your cluster:

akka.persistence.journal.redis.configuration-string = "contoso5.redis.cache.windows.net, contoso4.redis.cache.windows.net,user=akka-persistence,password=..."

Minimum command set

These are the minimum Redis commands that are needed by Akka.Persistence.Redis to work properly.

Redis Command	StackExchange.Redis Command
MULTI	Transaction
EXEC
DISCARD
SET	String Set
SETNX
SETEX
GET	String Get
LLEN	List Length
LRANGE	List Range
RPUSH	List Right Push
RPUSHX
LLEN
ZADD	Sorted Set Add
ZREMRANGEBYSCORE	Delete Sorted Set by Score Range
ZREVRANGEBYSCORE	Get Sorted Set by Score Range
ZRANGEBYSCORE
WITHSCORES
LIMIT
SSCAN	Scan
SMEMBERS
PUBSUB	Pub/Sub
PING
UNSUBSCRIBE
SUBSCRIBE
PSUBSCRIBE
PUNSUBSCRIBE
PUBLISH	Pub/Sub Publish

Serialization

Akka Persistence provided serializers wrap the user payload in an envelope containing all persistence-relevant information. Redis Journal uses provided Protobuf serializers for the wrapper types (e.g. IPersistentRepresentation), then the payload will be serialized using the user configured serializer.

The payload will be serialized using Akka.NET's serialization bindings for your events and snapshot objects. By default, all objects that do not have a specified serializer will use Newtonsoft.Json polymorphic serialization (your CLR types <--> JSON.)

This is fine for testing and initial phases of your development (while you’re still figuring out things and the data will not need to stay persisted forever). However, once you move to production you should really pick a different serializer for your payloads.

We highly recommend creating schema-based serialization definitions using MsgPack, Google.Protobuf, or something similar and configuring serialization bindings for those in your configuration: https://getakka.net/articles/networking/serialization.html#usage

Serialization of snapshots and payloads of Persistent messages is configurable with Akka’s Serialization infrastructure. For example, if an application wants to serialize

• payloads of type MyPayload with a custom MyPayloadSerializer and
• snapshots of type MySnapshot with a custom MySnapshotSerializer it must add

akka.actor {
  serializers {
    redis = "Akka.Serialization.YourOwnSerializer, YourOwnSerializer"
  }
  serialization-bindings {
    "Akka.Persistence.Redis.Journal.JournalEntry, Akka.Persistence.Redis" = redis
    "Akka.Persistence.Redis.Snapshot.SnapshotEntry, Akka.Persistence.Redis" = redis
  }
}