Machinery

Machinery is an asynchronous task queue/job queue based on distributed message passing.

So called tasks (or jobs if you like) are executed concurrently either by many workers on many servers or multiple worker processes on a single server using Golang's goroutines.

• First Steps
• Configuration
• Custom Logger
• Server
• Workers
• Tasks
  • Registering Tasks
  • Signatures
  • Supported Types
  • Sending Tasks
  • Delayed Tasks
  • Get Pending Tasks
  • Keeping Results
• Workflows
  • Groups
  • Chords
  • Chains
• Development
  • Requirements
  • Dependencies
  • Testing

First Steps

Add the Machinery library to your $GOPATH/src:

go get github.com/RichardKnop/machinery/v1

First, you will need to define some tasks. Look at sample tasks in example/tasks/tasks.go to see a few examples.

Second, you will need to launch a worker process:

go run example/machinery.go worker

Finally, once you have a worker running and waiting for tasks to consume, send some tasks:

go run example/machinery.go send

You will be able to see the tasks being processed asynchronously by the worker:

Configuration

Machinery has several configuration options. Configuration is encapsulated by a Config struct and injected as a dependency to objects that need it.

// Config holds all configuration for our program
type Config struct {
  Broker             string     `yaml:"broker"`
  DefaultQueue       string     `yaml:"default_queue"`
  ResultBackend      string     `yaml:"result_backend"`
  ResultsExpireIn    int        `yaml:"results_expire_in"`
  MaxWorkerInstances int        `yaml:"max_worker_instances"`
  AMQP               AMQPConfig `yaml:"amqp"`
  TLSConfig          *tls.Config
}

// QueueBindingArguments arguments which are used when binding to the exchange
type QueueBindingArguments map[string]interface{}

// AMQPConfig wraps RabbitMQ related configuration
type AMQPConfig struct {
  Exchange              string                `yaml:"exchange"`
  ExchangeType          string                `yaml:"exchange_type"`
  QueueBindingArguments QueueBindingArguments `yaml:"queue_binding_arguments"`
  BindingKey            string                `yaml:"binding_key"`
  PrefetchCount         int                   `yaml:"prefetch_count"`
}

Broker

A message broker. Currently supported brokers are:

AMQP

Use AMQP URL in the format:

amqp://[username:password@]@host[:port]

For example:

1. amqp://guest:guest@localhost:5672

Redis

Use Redis URL in one of these formats:

redis://[password@]host[port][/db_num]
redis+socket://[password@]/path/to/file.sock[:/db_num]

For example:

1. redis://127.0.0.1:6379, or with password redis://password@127.0.0.1:6379
2. redis+socket://password@/path/to/file.sock:/0

DefaultQueue

Default queue name, e.g. machinery_tasks.

ResultBackend

Result backend to use for keeping task states and results.

Currently supported backends are:

Redis

Use Redis URL in one of these formats:

redis://[password@]host[port][/db_num]
redis+socket://[password@]/path/to/file.sock[:/db_num]

For example:

1. redis://127.0.0.1:6379, or with password redis://password@127.0.0.1:6379
2. redis+socket://password@/path/to/file.sock:/0

Memcache

Use Memcache URL in the format:

memcache://host1[:port1][,host2[:port2],...[,hostN[:portN]]]

For example:

1. memcache://127.0.0.1:11211 for a single instance, or
2. memcache://10.0.0.1:11211,10.0.0.2:11211 for a cluster

AMQP

Use AMQP URL in the format:

amqp://[username:password@]@host[:port]

For example:

1. amqp://guest:guest@localhost:5672

Keep in mind AMQP is not recommended as a result backend. See Keeping Results

MongoDB

Use Mongodb URL in the format:

mongodb://[username:password@]host1[:port1][,host2[:port2],...[,hostN[:portN]]][/[database][?options]]

For example:

1. mongodb://127.0.0.1:27017/taskresults

See MongoDB docs for more information.

ResultsExpireIn

How long to store task results for in seconds. Defaults to 3600 (1 hour).

AMQP

RabbitMQ related configuration. Not neccessarry if you are using other broker/backend.

• Exchange: exchange name, e.g. machinery_exchange
• ExchangeType: exchange type, e.g. direct
• QueueBindingArguments: an optional map of additional arguments used when binding to an AMQP queue
• BindingKey: The queue is bind to the exchange with this key, e.g. machinery_task
• PrefetchCount: How many tasks to prefetch (set to 1 if you have long running tasks)

Custom Logger

You can define a custom logger by implementing the following interface:

type Interface interface {
  Print(...interface{})
  Printf(string, ...interface{})
  Println(...interface{})

  Fatal(...interface{})
  Fatalf(string, ...interface{})
  Fatalln(...interface{})

  Panic(...interface{})
  Panicf(string, ...interface{})
  Panicln(...interface{})
}

Then just set the logger in your setup code by calling Set function exported by github.com/RichardKnop/machinery/logger package:

logger.Set(myCustomLogger)

Server

A Machinery library must be instantiated before use. The way this is done is by creating a Server instance. Server is a base object which stores Machinery configuration and registered tasks. E.g.:

import (
  "github.com/RichardKnop/machinery/v1/config"
  machinery "github.com/RichardKnop/machinery/v1"
)

var cnf = config.Config{
  Broker:             "amqp://guest:guest@localhost:5672/",
  ResultBackend:      "amqp://guest:guest@localhost:5672/",
  MaxWorkerInstances: 0,
  AMQP:               config.AMQPConfig{
    Exchange:     "machinery_exchange",
    ExchangeType: "direct",
    DefaultQueue: "machinery_tasks",
    BindingKey:   "machinery_task",
  },
}

server, err := machinery.NewServer(&cnf)
if err != nil {
  // do something with the error
}

Workers

In order to consume tasks, you need to have one or more workers running. All you need to run a worker is a Server instance with registered tasks. E.g.:

worker := server.NewWorker("worker_name")
err := worker.Launch()
if err != nil {
  // do something with the error
}

Each worker will only consume registered tasks. For each task on the queue the Worker.Process() method will will be run in a goroutine. Use the MaxWorkerInstances config option to limit the number of concurrently running Worker.Process() calls (per worker). MaxWorkerInstances = 1 will serialize task execution. MaxWorkerInstances = 0 makes the number of concurrently executed tasks unlimited (default).

Tasks

Tasks are a building block of Machinery applications. A task is a function which defines what happens when a worker receives a message.

Each task needs to return an error as a last return value. In addition to error tasks can now return any number of arguments.

Examples of valid tasks:

func Add(args ...int64) (int64, error) {
  sum := int64(0)
  for _, arg := range args {
    sum += arg
  }
  return sum, nil
}

func Multiply(args ...int64) (int64, error) {
  sum := int64(1)
  for _, arg := range args {
    sum *= arg
  }
  return sum, nil
}

// You can use context.Context as first argument to tasks, useful for open tracing
func TaskWithContext(ctx context.Context, arg Arg) error {
  // ... use ctx ...
  return nil
}

// Tasks need to return at least error as a minimal requirement
func DummyTask(arg string) error {
  return errors.New(arg)
}

// You can also return multiple results from the task
func DummyTask2(arg1, arg2 string) (string, string error) {
  return arg1, arg2, nil
}

Registering Tasks

Before your workers can consume a task, you need to register it with the server. This is done by assigning a task a unique name:

server.RegisterTasks(map[string]interface{}{
  "add":      Add,
  "multiply": Multiply,
})

Tasks can also be registered one by one:

server.RegisterTask("add", Add)
server.RegisterTask("multiply", Multiply)

Simply put, when a worker receives a message like this:

{
  "UUID": "48760a1a-8576-4536-973b-da09048c2ac5",
  "Name": "add",
  "RoutingKey": "",
  "ETA": null,
  "GroupUUID": "",
  "GroupTaskCount": 0,
  "Args": [
    {
      "Type": "int64",
      "Value": 1,
    },
    {
      "Type": "int64",
      "Value": 1,
    }
  ],
  "Immutable": false,
  "OnSuccess": null,
  "OnError": null,
  "ChordCallback": null
}

It will call Add(1, 1). Each task should return an error as well so we can handle failures.

Ideally, tasks should be idempotent which means there will be no unintended consequences when a task is called multiple times with the same arguments.

Signatures

A signature wraps calling arguments, execution options (such as immutability) and success/error callbacks of a task so it can be sent across the wire to workers. Task signatures implement a simple interface:

// Arg represents a single argument passed to invocation fo a task
type Arg struct {
  Type  string
  Value interface{}
}

// Headers represents the headers which should be used to direct the task
type Headers map[string]interface{}

// Signature represents a single task invocation
type Signature struct {
  UUID           string
  Name           string
  RoutingKey     string
  ETA            *time.Time
  GroupUUID      string
  GroupTaskCount int
  Args           []Arg
  Headers        Headers
  Immutable      bool
  OnSuccess      []*Signature
  OnError        []*Signature
  ChordCallback  *Signature
}

UUID is a unique ID of a task. You can either set it yourself or it will be automatically generated.

Name is the unique task name by which it is registered against a Server instance.

RoutingKey is used for routing a task to correct queue. If you leave it empty, the default behaviour will be to set it to the default queue's binding key for direct exchange type and to the default queue name for other exchange types.

ETA is a timestamp used for delaying a task. if it's nil, the task will be published for workers to consume immediately. If it is set, the task will be delayed until the ETA timestamp.

GroupUUID, GroupTaskCount are useful for creating groups of tasks.

Args is a list of arguments that will be passed to the task when it is executed by a worker.

Headers is a list of headers that will be used when publishing the task to AMQP queue.

Immutable is a flag which defines whether a result of the executed task can be modified or not. This is important with OnSuccess callbacks. Immutable task will not pass its result to its success callbacks while a mutable task will prepend its result to args sent to callback tasks. Long story short, set Immutable to false if you want to pass result of the first task in a chain to the second task.

OnSuccess defines tasks which will be called after the task has executed successfully. It is a slice of task signature structs.

OnError defines tasks which will be called after the task execution fails. The first argument passed to error callbacks will be the error string returned from the failed task.

ChordCallback is used to create a callback to a group of tasks.

Supported Types

Machinery encodes tasks to JSON before sending them to the broker. Task results are also stored in the backend as JSON encoded strings. Therefor only types with native JSON representation can be supported. Currently supported types are:

• bool
• int
• int8
• int16
• int32
• int64
• uint
• uint8
• uint16
• uint32
• uint64
• float32
• float64
• string

Sending Tasks

Tasks can be called by passing an instance of Signature to an Server instance. E.g:

import (
  "github.com/RichardKnop/machinery/v1/tasks"
)

signature := &tasks.Signature{
  Name: "add",
  Args: []tasks.Arg{
    {
      Type:  "int64",
      Value: 1,
    },
    {
      Type:  "int64",
      Value: 1,
    },
  },
}

asyncResult, err := server.SendTask(signature)
if err != nil {
  // failed to send the task
  // do something with the error
}

Delayed Tasks

You can delay a task by setting the ETA timestamp field on the task signature.

// Delay the task by 5 seconds
eta := time.Now().UTC().Add(time.Second * 5)
signature.ETA = &eta

asyncResult, err := server.SendTask(signature)
if err != nil {
  // failed to send the task
  // do something with the error
}

Get Pending Tasks

Tasks currently waiting in the queue to be consumed by workers can be inspected, e.g.:

server.GetBroker().GetPendingTasks("some_queue")

Currently only supported by Redis broker.

Keeping Results

If you configure a result backend, the task states and results will be persisted. Possible states:

const (
  PendingState  = "PENDING"
  ReceivedState = "RECEIVED"
  StartedState  = "STARTED"
  SuccessState  = "SUCCESS"
  FailureState  = "FAILURE"
)

When using AMQP as a result backend, task states will be persisted in separate queues for each task. Although RabbitMQ can scale up to thousands of queues, it is strongly advised to use a better suited result backend (e.g. Memcache) when you are expecting to run a large number of parallel tasks.

// TaskResult represents an actual return value of a processed task
type TaskResult struct {
  Type  string      `bson:"type"`
  Value interface{} `bson:"value"`
}

// TaskState represents a state of a task
type TaskState struct {
  TaskUUID  string        `bson:"_id"`
  State     string        `bson:"state"`
  Results   []*TaskResult `bson:"results"`
  Error     string        `bson:"error"`
}

// GroupMeta stores useful metadata about tasks within the same group
// E.g. UUIDs of all tasks which are used in order to check if all tasks
// completed successfully or not and thus whether to trigger chord callback
type GroupMeta struct {
  GroupUUID      string   `bson:"_id"`
  TaskUUIDs      []string `bson:"task_uuids"`
  ChordTriggered bool     `bson:"chord_trigerred"`
}

TaskResult represents a slice of return values of a processed task.

TaskState struct will be serialized and stored every time a task state changes.

GroupMeta stores useful metadata about tasks within the same group. E.g. UUIDs of all tasks which are used in order to check if all tasks completed successfully or not and thus whether to trigger chord callback.

AsyncResult object allows you to check for the state of a task:

taskState := asyncResult.GetState()
fmt.Printf("Current state of %v task is:\n", taskState.TaskUUID)
fmt.Println(taskState.State)

There are couple of convenient me methods to inspect the task status:

asyncResult.GetState().IsCompleted()
asyncResult.GetState().IsSuccess()
asyncResult.GetState().IsFailure()

You can also do a synchronous blocking call to wait for a task result:

results, err := asyncResult.Get()
if err != nil {
  // getting result of a task failed
  // do something with the error
}
for _, result := range results {
  fmt.Println(result.Interface())
}

Workflows

Running a single asynchronous task is fine but often you will want to design a workflow of tasks to be executed in an orchestrated way. There are couple of useful functions to help you design workflows.

Groups

Group is a set of tasks which will be executed in parallel, independent of each other. E.g.:

import (
  "github.com/RichardKnop/machinery/v1/tasks"
  machinery "github.com/RichardKnop/machinery/v1"
)

signature1 := tasks.Signature{
  Name: "add",
  Args: []tasks.Arg{
    {
      Type:  "int64",
      Value: 1,
    },
    {
      Type:  "int64",
      Value: 1,
    },
  },
}

signature2 := tasks.Signature{
  Name: "add",
  Args: []tasks.Arg{
    {
      Type:  "int64",
      Value: 5,
    },
    {
      Type:  "int64",
      Value: 5,
    },
  },
}

group := tasks.NewGroup(&signature1, &signature2)
asyncResults, err := server.SendGroup(group)
if err != nil {
  // failed to send the group
  // do something with the error
}

SendGroup returns a slice of AsyncResult objects. So you can do a blocking call and wait for the result of groups tasks:

for _, asyncResult := range asyncResults {
  results, err := asyncResult.Get()
  if err != nil {
    // getting result of a task failed
    // do something with the error
  }
  for _, result := range results {
    fmt.Println(result.Interface())
  }
}

Chords

Chord allows you to define a callback to be executed after all tasks in a group finished processing, e.g.:

import (
  "github.com/RichardKnop/machinery/v1/tasks"
  machinery "github.com/RichardKnop/machinery/v1"
)

signature1 := tasks.Signature{
  Name: "add",
  Args: []tasks.Arg{
    {
      Type:  "int64",
      Value: 1,
    },
    {
      Type:  "int64",
      Value: 1,
    },
  },
}

signature2 := tasks.Signature{
  Name: "add",
  Args: []tasks.Arg{
    {
      Type:  "int64",
      Value: 5,
    },
    {
      Type:  "int64",
      Value: 5,
    },
  },
}

signature3 := tasks.Signature{
  Name: "multiply",
}

group := tasks.NewGroup(&signature1, &signature2)
chord := tasks.NewChord(group, &signature3)
chordAsyncResult, err := server.SendChord(chord)
if err != nil {
  // failed to send the chord
  // do something with the error
}

The above example executes task1 and task2 in parallel, aggregates their results and passes them to task3. Therefore what would end up happening is:

multiply(add(1, 1), add(5, 5))

More explicitly:

(1 + 1) * (5 + 5) = 2 * 10 = 20

SendChord returns ChordAsyncResult which follows AsyncResult's interface. So you can do a blocking call and wait for the result of the callback:

results, err := chordAsyncResult.Get()
if err != nil {
  // getting result of a chord failed
  // do something with the error
}
for _, result := range results {
  fmt.Println(result.Interface())
}

Chains

Chain is simply a set of tasks which will be executed one by one, each successful task triggering the next task in the chain. E.g.:

import (
  "github.com/RichardKnop/machinery/v1/tasks"
  machinery "github.com/RichardKnop/machinery/v1"
)

signature1 := tasks.Signature{
  Name: "add",
  Args: []tasks.Arg{
    {
      Type:  "int64",
      Value: 1,
    },
    {
      Type:  "int64",
      Value: 1,
    },
  },
}

signature2 := tasks.Signature{
  Name: "add",
  Args: []tasks.Arg{
    {
      Type:  "int64",
      Value: 5,
    },
    {
      Type:  "int64",
      Value: 5,
    },
  },
}

signature3 := tasks.Signature{
  Name: "multiply",
  Args: []tasks.Arg{
    {
      Type:  "int64",
      Value: 4,
    },
  },
}

chain := tasks.NewChain(&signature1, &signature2, &signature3)
chainAsyncResult, err := server.SendChain(chain)
if err != nil {
  // failed to send the chain
  // do something with the error
}

The above example executes task1, then task2 and then task3, passing the result of each task to the next task in the chain. Therefore what would end up happening is:

multiply(add(add(1, 1), 5, 5), 4)

More explicitly:

((1 + 1) + (5 + 5)) * 4 = 12 * 4 = 48

SendChain returns ChainAsyncResult which follows AsyncResult's interface. So you can do a blocking call and wait for the result of the whole chain:

results, err := chainAsyncResult.Get()
if err != nil {
  // getting result of a chain failed
  // do something with the error
}
for _, result := range results {
  fmt.Println(result.Interface())
}

Development

Requirements

• Go
• RabbitMQ
• Redis (optional)
• Memcached (optional)

On OS X systems, you can install requirements using Homebrew:

brew install go
brew install rabbitmq
brew install redis
brew install memcached

Dependencies

According to Go 1.5 Vendor experiment, all dependencies are stored in the vendor directory. This approach is called vendoring and is the best practice for Go projects to lock versions of dependencies in order to achieve reproducible builds.

To update dependencies during development:

make update-deps

To install dependencies:

make install-deps

Testing

To run tests:

$ make test

In order to enable integration tests, you will need to export few environment variables:

export AMQP_URL=amqp://guest:guest@localhost:5672/
export REDIS_URL=127.0.0.1:6379
export MEMCACHE_URL=127.0.0.1:11211
export MONGODB_URL=mongodb://{host}:{port}/{database}

I recommend to run the integration tests when making changes to the code. Due to Machinery being composed of several parts (worker, client) which run independently of each other, integration tests are important to verify everything works as expected.