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Overview

You can run a Scheduler alongside with the Server to process tasks periodically. Scheduler enqueues tasks at regular intervals, that are then executed by available worker servers in the cluster.

You have to ensure only a single scheduler is running for a schedule at a time, otherwise you’d end up with duplicate tasks. Using a centralized approach means the schedule doesn’t have to be synchronized, and the service can operate without using locks.

If you need to dynamically add and remove periodic tasks, use PeriodicTaskManager instead of using Scheduler directly. See this wiki page for more details.

Time Zones

The periodic task schedules uses the UTC time zone by default, but you can change the time zone used using the SchedulerOpts.

// Example of using America/Los_Angeles timezone instead of the default UTC timezone.
loc, err := time.LoadLocation("America/Los_Angeles")
if err != nil {
    panic(err)
}
scheduler := asynq.NewScheduler(
    redisConnOpt, 
    &asynq.SchedulerOpts{
        Location: loc,
    },
)

Entries

To enqueue a task periodically you have to register an entry with the scheduler.

scheduler := asynq.NewScheduler(redisConnOpt, nil)

task := asynq.NewTask("example_task", nil)

// You can use cron spec string to specify the schedule. 
entryID, err := scheduler.Register("* * * * *", task)
if err != nil {
    log.Fatal(err)
}
log.Printf("registered an entry: %q\n", entryID)

// You can use "@every <duration>" to specify the interval.
entryID, err = scheduler.Register("@every 30s", task)
if err != nil {
    log.Fatal(err)
}
log.Printf("registered an entry: %q\n", entryID)

// You can also pass options.
entryID, err = scheduler.Register("@every 24h", task, asynq.Queue("myqueue"))
if err != nil {
    log.Fatal(err)
}
log.Printf("registered an entry: %q\n", entryID)

Run the Scheduler

To start the scheduler, call Run on the scheduler.

scheduler := asynq.NewScheduler(redisConnOpt, nil)

// ... Register tasks

if err := scheduler.Run(); err != nil {
    log.Fatal(err)
}

The call to Run will wait for TERM or INT signal (e.g. Ctrl-C keypress).

Error Handling

You can provide a function to handle an error if the scheduler could not enqueue a task.

func handleEnqueueError(task *asynq.Task, opts []asynq.Option, err error) {
    // your error handling logic
}

scheduler := asynq.NewScheduler(
    redisConnOpt, 
    &asynq.SchedulerOpts{
        EnqueueErrorHandler: handleEnqueueError,
    },
)

Inspection via CLI

The CLI has a subcommand cron to inspect scheduler entries.

To see all entries from the currently running scheduler, you can run:

asynq cron ls

This command will output a list of entries each with its IDs, Schedule Spec, Next enqueue time, Previous enqueue time.

You can also see a history of each entry by running:

asynq cron history <entryID>