goakt

README

Go-Akt

Distributed Go actor framework to build reactive and distributed system in golang using protocol buffers as actor messages.

GoAkt is highly scalable and available when running in cluster mode. It comes with the necessary features require to build a distributed actor-based system without sacrificing performance and reliability. With GoAkt, you can instantly create a fast, scalable, distributed system across a cluster of computers.

If you are not familiar with the actor model, the blog post from Brian Storti here is an excellent and short introduction to the actor model. Also, check reference section at the end of the post for more material regarding actor model.

Table of Content

• Design Principles
• Features
  • Actors
  • Actor System
  • Behaviors
  • Mailbox
  • Dead Letters
  • Messaging
  • Scheduler
  • Stashing
  • Remoting
  • Clustering
  • Logging
  • Testkit
• Use Cases
• Installation
• Clustering
  • Operation Guides
  • Discovery Providers
    • Kubernetes
    • mDNS
    • NATS
• Examples
• Contribution
  • Local Test and Linter
• Benchmark

Design Principles

This framework has been designed:

• to be very minimalistic - it caters for the core component of an actor framework as stated by the father of the actor framework here.
• to be very easy to use.
• to have a clear and defined contract for messages - no need to implement/hide any sort of serialization.
• to lean on proven tech and standards - no need to reinvent solved problems.
• to be very fast.
• to expose interfaces for custom integrations rather than making it convoluted with unnecessary features.

Features

Actors

The fundamental building blocks of Go-Akt are actors.

• They are independent, isolated unit of computation with their own state.
• They can be long-lived actors or be passivated after some period of time that is configured during their creation.
• They are automatically thread-safe without having to use locks or any other shared-memory synchronization mechanisms.
• They can be stateful and stateless depending upon the system to build.
• Every actor in Go-Akt:
  • has a process id PID. Via the process id any allowable action can be executed by the actor.
  • has a lifecycle via the following methods: PreStart, PostStop. It means it can live and die like any other process.
  • handles and responds to messages via the method Receive. While handling messages it can:
  • create other (child) actors via their process id PID SpawnChild method
  • send messages to other actors locally or remotely via their process id PID Ask, RemoteAsk(request/response fashion) and Tell, RemoteTell(fire-and-forget fashion) methods
  • stop (child) actors via their process id PID
  • watch/unwatch (child) actors via their process id PID Watch and UnWatch methods
  • supervise the failure behavior of (child) actors. The supervisory strategy to adopt is set during its creation:
  • Restart and Stop directive are supported at the moment.
  • remotely lookup for an actor on another node via their process id PID RemoteLookup. This allows it to send messages remotely via RemoteAsk or RemoteTell methods
  • stash/unstash messages. See Stashing
  • can adopt various form using the Behavior feature
  • can be restarted (respawned)
  • can be gracefully stopped (killed). Every message in the mailbox prior to stoppage will be processed within a configurable time period.

Actor System

Without an actor system, it is not possible to create actors in Go-Akt. Only a single actor system is recommended to be created per application when using Go-Akt. At the moment the single instance is not enforced in Go-Akt, this simple implementation is left to the discretion of the developer. To create an actor system one just need to use the NewActorSystem method with the various Options. Go-Akt ActorSystem has the following characteristics:

• Actors lifecycle management (Spawn, Kill, ReSpawn)
• Concurrency and Parallelism - Multiple actors can be managed and execute their tasks independently and concurrently. This helps utilize multicore processors efficiently.
• Location Transparency - The physical location of actors is abstracted. Remote actors can be accessed via their address once remoting is enabled.
• Fault Tolerance and Supervision - Set during the creation of the actor system.
• Actor Addressing - Every actor in the ActorSystem has an address.

Behaviors

Actors in Go-Akt have the power to switch their behaviors at any point in time. When you change the actor behavior, the new behavior will take effect for all subsequent messages until the behavior is changed again. The current message will continue processing with the existing behavior. You can use Stashing to reprocess the current message with the new behavior.

To change the behavior, call the following methods on the ReceiveContext interface when handling a message:

• Become - switches the current behavior of the actor to a new behavior.
• UnBecome - resets the actor behavior to the default one which is the Actor.Receive method.
• BecomeStacked - sets a new behavior to the actor to the top of the behavior stack, while maintaining the previous ones.
• UnBecomeStacked() - sets the actor behavior to the previous behavior before BecomeStacked() was called. This only works with BecomeStacked().

Mailbox

Once can implement a custom mailbox. See Mailbox. The default mailbox makes use of buffered channels.

Dead Letters

Dead letters are basically messages that cannot be delivered or that were not handled by a given actor. Those messages are encapsulated in an event called DeadletterEvent. Dead letters are automatically emitted when a message cannot be delivered to actors' mailbox or when an Ask times out. Also, one can emit dead letters from the receiving actor by using the ctx.Unhandled() method. This is useful instead of panicking when the receiving actor does not know how to handle a particular message. Dead letters are not propagated over the network, there are tied to the local actor system. To receive the dead letter, you just need to call the actor system Subscribe and specify the Event_DEAD_LETTER event type.

Messaging

Communication between actors is achieved exclusively through message passing. In Go-Akt Google Protocol Buffers is used to define messages. The choice of protobuf is due to easy serialization over wire and strong schema definition.

Scheduler

You can schedule sending messages to actor that will be acted upon in the future. To achieve that you can use the following methods on the Actor System:

• ScheduleOnce - will send the given message to a local actor after a given interval
• RemoteScheduleOnce - will send the given message to a remote actor after a given interval. This requires remoting to be enabled on the actor system.
• ScheduleWithCron - will send the given message to a local actor using a cron expression.
• RemoteScheduleWithCron - will send the given message to a remote actor using a cron expression. This requires remoting to be enabled on the actor system.

Cron Expression Format

Field Name	Mandatory	Allowed Values	Allowed Special Characters
Seconds	YES	0-59	, - * /
Minutes	YES	0-59	, - * /
Hours	YES	0-23	, - * /
Day of month	YES	1-31	, - * ? /
Month	YES	1-12 or JAN-DEC	, - * /
Day of week	YES	1-7 or SUN-SAT	, - * ? /
Year	NO	empty, 1970-	, - * /

Note

When running the actor system in a cluster only one instance of a given scheduled message will be running across the entire cluster.

Stashing

Stashing is a mechanism you can enable in your actors, so they can temporarily stash away messages they cannot or should not handle at the moment. Another way to see it is that stashing allows you to keep processing messages you can handle while saving for later messages you can't. Stashing are handled by Go-Akt out of the actor instance just like the mailbox, so if the actor dies while processing a message, all messages in the stash are processed. This feature is usually used together with Become/UnBecome, as they fit together very well, but this is not a requirement.

It’s recommended to avoid stashing too many messages to avoid too much memory usage. If you try to stash more messages than the capacity the actor will panic. To use the stashing feature, call the following methods on the ReceiveContext interface when handling a message:

• Stash() - adds the current message to the stash buffer.
• Unstash() - unstashes the oldest message in the stash and prepends to the stash buffer.
• UnstashAll() - unstashes all messages from the stash buffer and prepends in the mailbox. Messages will be processed in the same order they arrived. The stash buffer will be empty after processing all messages, unless an exception is thrown or messages are stashed while unstashing.

Remoting

This allows remote actors to communicate. The underlying technology is gRPC.

Cluster

This offers simple scalability, partitioning (sharding), and re-balancing out-of-the-box. Go-Akt nodes are automatically discovered. See Clustering.

Logging

A simple logging interface to allow custom logger to be implemented instead of using the default logger.

Testkit

To help implement unit tests in GoAkt-based applications. See Testkit

Use Cases

• Event-Driven programming
• Event Sourcing and CQRS - eGo
• Highly Available, Fault-Tolerant Distributed Systems

Installation

go get github.com/tochemey/goakt

Clustering

The cluster engine depends upon the discovery mechanism to find other nodes in the cluster. Under the hood, it leverages Olric to scale out and guarantee performant, reliable persistence, simple scalability, partitioning (sharding), and re-balancing out-of-the-box.

At the moment the following providers are implemented:

• the kubernetes api integration is fully functional
• the mDNS and DNS-SD
• the NATS integration is fully functional

Note: One can add additional discovery providers using the following interface

In addition, one needs to set the following environment variables irrespective of the discovery provider to help identify the host node on which the cluster service is running:

• NODE_NAME: the node name. For instance in kubernetes one can just get it from the metadata.name
• NODE_IP: the node host address. For instance in kubernetes one can just get it from the status.podIP
• GOSSIP_PORT: the gossip protocol engine port.
• CLUSTER_PORT: the cluster port to help communicate with other GoAkt nodes in the cluster
• REMOTING_PORT: help remoting communication between actors

Note: Depending upon the discovery provider implementation, the GOSSIP_PORT and CLUSTER_PORT can be the same. The same applies to NODE_NAME and NODE_IP. This is up to the discretion of the implementation

Operations Guide

The following outlines the cluster mode operations which can help have a healthy GoAkt cluster:

• One can start a single node cluster or a multiple nodes cluster.
• One can add more nodes to the cluster which will automatically discover the cluster.
• One can remove nodes. However, to avoid losing data, one need to scale down the cluster to the minimum number of nodes which started the cluster.

Built-in Discovery Providers

Kubernetes Discovery Provider Setup

To get the kubernetes discovery working as expected, the following pod labels need to be set:

• app.kubernetes.io/part-of: set this label with the actor system name
• app.kubernetes.io/component: set this label with the application name
• app.kubernetes.io/name: set this label with the application name

In addition, each node is required to have three different ports open with the following ports name for the cluster engine to work as expected:

• gossip-port: help the gossip protocol engine. This is actually the kubernetes discovery port
• cluster-port: help the cluster engine to communicate with other GoAkt nodes in the cluster
• remoting-port: help for remoting messaging between actors

Get Started

const (
  namespace          = "default"
  applicationName    = "accounts"
  actorSystemName    = "AccountsSystem"
)
// instantiate the k8 discovery provider
disco := kubernetes.NewDiscovery()
// define the discovery options
discoOptions := discovery.Config{
    kubernetes.ApplicationName: applicationName,
    kubernetes.ActorSystemName: actorSystemName,
    kubernetes.Namespace:       namespace,
}
// define the service discovery
serviceDiscovery := discovery.NewServiceDiscovery(disco, discoOptions)
// pass the service discovery when enabling cluster mode in the actor system

Role Based Access

You’ll also have to grant the Service Account that your pods run under access to list pods. The following configuration can be used as a starting point. It creates a Role, pod-reader, which grants access to query pod information. It then binds the default Service Account to the Role by creating a RoleBinding. Adjust as necessary:

kind: Role
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: pod-reader
rules:
  - apiGroups: [""] # "" indicates the core API group
    resources: ["pods"]
    verbs: ["get", "watch", "list"]
---
kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: read-pods
subjects:
  # Uses the default service account. Consider creating a new one.
  - kind: ServiceAccount
    name: default
roleRef:
  kind: Role
  name: pod-reader
  apiGroup: rbac.authorization.k8s.io

Sample Project

A working example can be found here with a small doc showing how to run it.

mDNS Discovery Provider Setup

• Service Name: the service name
• Domain: The mDNS discovery domain
• Port: The mDNS discovery port
• IPv6: States whether to lookup for IPv6 addresses.

NATS Discovery Provider Setup

To use the NATS discovery provider one needs to provide the following:

• NATS Server Address: the NATS Server address
• NATS Subject: the NATS subject to use
• Actor System Name: the actor system name
• Application Name: the application name

const (
  natsServerAddr = "nats://localhost:4248"
  natsSubject = "goakt-gossip"
  applicationName        = "accounts"
  actorSystemName = "AccountsSystem"
)
// instantiate the NATS discovery provider
disco := nats.NewDiscovery()
// define the discovery options
discoOptions := discovery.Config{
  ApplicationName: applicationName,
  ActorSystemName: actorSystemName,
  NatsServer:      natsServer,
  NatsSubject:     natsSubject,
}
// define the service discovery
serviceDiscovery := discovery.NewServiceDiscovery(disco, discoOptions)
// pass the service discovery when enabling cluster mode in the actor system

Examples

Kindly check out the examples' folder.

Contribution

Contributions are welcome! The project adheres to Semantic Versioning and Conventional Commits. This repo uses Earthly.

To contribute please:

• Fork the repository
• Create a feature branch
• Submit a pull request

Test & Linter

Prior to submitting a pull request, please run:

earthly +test

Benchmark

One can run the benchmark test: go test -bench=. -benchtime 2s -count 5 -benchmem -cpu 8 -run notest from the bench package or just run the command make bench.