cronalt

cronalt is a Golang job scheduling package that allows you to run jobs at a given interval.

• Scheduler runs in-process
• Runtime safety (avoids reflection)
• Pluggable and extensible

cronalt is inspired by gocron

Install using go modules

go get github.com/ahmedalhulaibi/cronalt@v1.0.0

Getting started

See internal/examples/basic directory for a simple example

Concepts

Job

The job is simply aware of the task it's provided. It is defined as an interface. Jobs can be extended/wrapped using a decorator to extend functionality.

Job Timer

A Job Timer informs the Scheduler how long to wait before triggering the next run for a given Job. The Job Timer is also defined as an interface to allow for irregular scheduling.

Scheduler

The Scheduler orchestrates all Jobs. It starts all the jobs and stops all the jobs. For each job, an individual goroutine is kicked off with its Job Timer informing the routine how the job should be scheduled.

How Do I...?

How do I lock a job in a distributed system (K8s, Nomad, etc.)?

Decorate your job with a locker implementation.

See internal/examples/redsync for an example.

Please beware that using Redis for locks as demonstrated in the example can lead to unintended consequences. This example is not tested in production. If you're worried about race conditions, consider redesigning your process such that it does not require a distributed lock.

Additional reading:

• How to do distributed locking by Martin Kleppmann
• Is Redlock safe? by Salvatore Sanfilippo
• redlock: unsafe at any time by Alisdair Sullivan

How do I handle an error if my job fails?

Decorate your job with an error handler implementation.

See internal/examples/errorhandler for an example.

How do I stop the scheduler if a job keeps failing?

Decorate all your jobs with a circuit breaker which cancels the parent context. This will stop the entire process, not just the individual routine.

See internal/examples/circuitbreaker for an example

How do I propagate custom fields in context?

Decorate your job with a context decorator.

See internal/examples/runid for an example

How do I dynamically add and remove jobs?

This is not supported out of the box.

See internal/examples/dynamicscheduling for an example of a dynamic scheduler built around cronalt.Scheduler.

How do I capture the number of times my job has run?

Decorate your job with a counter. See extensions/counter/counter.go for the job decorator.