# Asynq

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## Overview

Asynq is a Go library for queueing tasks and processing them in the background with workers. It is backed by Redis and it is designed to have a low barrier to entry. It should be integrated in your web stack easily.

Highlevel overview of how Asynq works:

- Client puts task on a queue
- Server pulls task off queues and starts a worker goroutine for each task
- Tasks are processed concurrently by multiple workers

Task queues are used as a mechanism to distribute work across multiple machines.  
A system can consist of multiple worker servers and brokers, giving way to high availability and horizontal scaling.

![Task Queue Diagram](/docs/assets/overview.png)

## Stability and Compatibility

**Important Note**: Current major version is zero (v0.x.x) to accomodate rapid development and fast iteration while getting early feedback from users (Feedback on APIs are appreciated!). The public API could change without a major version update before v1.0.0 release.

**Status**: The library is currently undergoing heavy development with frequent, breaking API changes.

## Features

- Guaranteed [at least one execution](https://www.cloudcomputingpatterns.org/at_least_once_delivery/) of a task
- Scheduling of tasks
- Durability since tasks are written to Redis
- [Retries](https://github.com/hibiken/asynq/wiki/Task-Retry) of failed tasks
- Automatic recovery of tasks in the event of a worker crash
- [Weighted priority queues](https://github.com/hibiken/asynq/wiki/Priority-Queues#weighted-priority-queues)
- [Strict priority queues](https://github.com/hibiken/asynq/wiki/Priority-Queues#strict-priority-queues)
- Low latency to add a task since writes are fast in Redis
- De-duplication of tasks using [unique option](https://github.com/hibiken/asynq/wiki/Unique-Tasks)
- Allow [timeout and deadline per task](https://github.com/hibiken/asynq/wiki/Task-Timeout-and-Cancelation)
- [Flexible handler interface with support for middlewares](https://github.com/hibiken/asynq/wiki/Handler-Deep-Dive)
- [Ability to pause queue](/tools/asynq/README.md#pause) to stop processing tasks from the queue
- [Support Redis Sentinels](https://github.com/hibiken/asynq/wiki/Automatic-Failover) for HA
- [CLI](#command-line-tool) to inspect and remote-control queues and tasks

## Quickstart

First, make sure you are running a Redis server locally.

```sh
$ redis-server
```

Next, write a package that encapsulates task creation and task handling.

```go
package tasks

import (
    "fmt"

    "github.com/hibiken/asynq"
)

// A list of task types.
const (
    EmailDelivery   = "email:deliver"
    ImageProcessing = "image:process"
)

//----------------------------------------------
// Write a function NewXXXTask to create a task.
// A task consists of a type and a payload.
//----------------------------------------------

func NewEmailDeliveryTask(userID int, tmplID string) *asynq.Task {
    payload := map[string]interface{}{"user_id": userID, "template_id": tmplID}
    return asynq.NewTask(EmailDelivery, payload)
}

func NewImageProcessingTask(src, dst string) *asynq.Task {
    payload := map[string]interface{}{"src": src, "dst": dst}
    return asynq.NewTask(ImageProcessing, payload)
}

//---------------------------------------------------------------
// Write a function HandleXXXTask to handle the input task.
// Note that it satisfies the asynq.HandlerFunc interface.
// 
// Handler doesn't need to be a function. You can define a type 
// that satisfies asynq.Handler interface. See examples below.
//---------------------------------------------------------------

func HandleEmailDeliveryTask(ctx context.Context, t *asynq.Task) error {
    userID, err := t.Payload.GetInt("user_id")
    if err != nil {
        return err
    }
    tmplID, err := t.Payload.GetString("template_id")
    if err != nil {
        return err
    }
    fmt.Printf("Send Email to User: user_id = %d, template_id = %s\n", userID, tmplID)
    // Email delivery logic ...
    return nil
}

// ImageProcessor implements asynq.Handler interface.
type ImageProcesser struct {
    // ... fields for struct
}

func (p *ImageProcessor) ProcessTask(ctx context.Context, t *asynq.Task) error {
    src, err := t.Payload.GetString("src")
    if err != nil {
        return err
    }
    dst, err := t.Payload.GetString("dst")
    if err != nil {
        return err
    }
    fmt.Printf("Process image: src = %s, dst = %s\n", src, dst)
    // Image processing logic ...
    return nil
}

func NewImageProcessor() *ImageProcessor {
    // ... return an instance
}
```

In your web application code, import the above package and use [`Client`](https://pkg.go.dev/github.com/hibiken/asynq?tab=doc#Client) to put tasks on the queue.  
A task will be processed asynchronously by a background worker as soon as the task gets enqueued.  
Scheduled tasks will be stored in Redis and will be enqueued at the specified time.

```go
package main

import (
    "time"

    "github.com/hibiken/asynq"
    "your/app/package/tasks"
)

const redisAddr = "127.0.0.1:6379"

func main() {
    r := asynq.RedisClientOpt{Addr: redisAddr}
    c := asynq.NewClient(r)
    defer c.Close()

    // ------------------------------------------------------
    // Example 1: Enqueue task to be processed immediately.
    //            Use (*Client).Enqueue method.
    // ------------------------------------------------------

    t := tasks.NewEmailDeliveryTask(42, "some:template:id")
    res, err := c.Enqueue(t)
    if err != nil {
        log.Fatal("could not enqueue task: %v", err)
    }
    fmt.Printf("Enqueued Result: %+v\n", res)


    // ------------------------------------------------------------
    // Example 2: Schedule task to be processed in the future.
    //            Use (*Client).EnqueueIn or (*Client).EnqueueAt.
    // ------------------------------------------------------------

    t = tasks.NewEmailDeliveryTask(42, "other:template:id")
    res, err = c.EnqueueIn(24*time.Hour, t)
    if err != nil {
        log.Fatal("could not schedule task: %v", err)
    }
    fmt.Printf("Enqueued Result: %+v\n", res)


    // ----------------------------------------------------------------------------
    // Example 3: Set options to tune task processing behavior.
    //            Options include MaxRetry, Queue, Timeout, Deadline, Unique etc.
    // ----------------------------------------------------------------------------

    c.SetDefaultOptions(tasks.ImageProcessing, asynq.MaxRetry(10), asynq.Timeout(time.Minute))

    t = tasks.NewImageProcessingTask("some/blobstore/url", "other/blobstore/url")
    res, err = c.Enqueue(t)
    if err != nil {
        log.Fatal("could not enqueue task: %v", err)
    }
    fmt.Printf("Enqueued Result: %+v\n", res)

    // ---------------------------------------------------------------------------
    // Example 4: Pass options to tune task processing behavior at enqueue time.
    //            Options passed at enqueue time override default ones, if any.
    // ---------------------------------------------------------------------------

    t = tasks.NewImageProcessingTask("some/blobstore/url", "other/blobstore/url")
    res, err = c.Enqueue(t, asynq.Queue("critical"), asynq.Timeout(30*time.Second))
    if err != nil {
        log.Fatal("could not enqueue task: %v", err)
    }
    fmt.Printf("Enqueued Result: %+v\n", res)
}
```

Next, create a worker server to process these tasks in the background.  
To start the background workers, use [`Server`](https://pkg.go.dev/github.com/hibiken/asynq?tab=doc#Server) and provide your [`Handler`](https://pkg.go.dev/github.com/hibiken/asynq?tab=doc#Handler) to process the tasks.

You can optionally use [`ServeMux`](https://pkg.go.dev/github.com/hibiken/asynq?tab=doc#ServeMux) to create a handler, just as you would with [`"net/http"`](https://golang.org/pkg/net/http/) Handler.

```go
package main

import (
    "log"

    "github.com/hibiken/asynq"
    "your/app/package/tasks"
)

const redisAddr = "127.0.0.1:6379"

func main() {
    r := asynq.RedisClientOpt{Addr: redisAddr}

    srv := asynq.NewServer(r, asynq.Config{
        // Specify how many concurrent workers to use
        Concurrency: 10,
        // Optionally specify multiple queues with different priority.
        Queues: map[string]int{
            "critical": 6,
            "default":  3,
            "low":      1,
        },
        // See the godoc for other configuration options
    })

    // mux maps a type to a handler
    mux := asynq.NewServeMux()
    mux.HandleFunc(tasks.EmailDelivery, tasks.HandleEmailDeliveryTask)
    mux.Handle(tasks.ImageProcessing, tasks.NewImageProcessor())
    // ...register other handlers...

    if err := srv.Run(mux); err != nil {
        log.Fatalf("could not run server: %v", err)
    }
}
```

For a more detailed walk-through of the library, see our [Getting Started Guide](https://github.com/hibiken/asynq/wiki/Getting-Started).

To Learn more about `asynq` features and APIs, see our [Wiki](https://github.com/hibiken/asynq/wiki) and [godoc](https://godoc.org/github.com/hibiken/asynq).

## Command Line Tool

Asynq ships with a command line tool to inspect the state of queues and tasks.

Here's an example of running the `stats` command.

![Gif](/docs/assets/demo.gif)

For details on how to use the tool, refer to the tool's [README](/tools/asynq/README.md).

## Installation

To install `asynq` library, run the following command:

```sh
go get -u github.com/hibiken/asynq
```

To install the CLI tool, run the following command:

```sh
go get -u github.com/hibiken/asynq/tools/asynq
```

## Requirements

| Dependency                 | Version |
| -------------------------- | ------- |
| [Redis](https://redis.io/) | v2.8+   |
| [Go](https://golang.org/)  | v1.13+  |

## Contributing

We are open to, and grateful for, any contributions (Github issues/pull-requests, feedback on Gitter channel, etc) made by the community.
Please see the [Contribution Guide](/CONTRIBUTING.md) before contributing.

## Acknowledgements

- [Sidekiq](https://github.com/mperham/sidekiq) : Many of the design ideas are taken from sidekiq and its Web UI
- [RQ](https://github.com/rq/rq) : Client APIs are inspired by rq library.
- [Cobra](https://github.com/spf13/cobra) : Asynq CLI is built with cobra

## License

Asynq is released under the MIT license. See [LICENSE](https://github.com/hibiken/asynq/blob/master/LICENSE).
