grontab

damdo/grontab

🕒 🔄 lib for parallel & persistent job scheduling and running, like crontab but for Go

grontab provides a simple way to time schedule *nix commands the same way we are all accustomed to do in crontab, thanks to the stable robfig/cron golang library.

It works as a normal golang package and provides persistency of the scheduled jobs across restarts thanks to a local k/v storage built with the lightning fast coreos/bbolt

FEATURES:

• crontab syntax : stable crontab like syntax for scheduling
• parallel/non parallel : jobs execution in parallel or not at the same schedule
• persistency : jobs persist across restarts
• consistency : jobs consistency and duplicate avoidance due to lightning fast ACID transactions in bbolt
• safe and tested : comes with high test coverage and it has been already used in production for several services and considered safe

It doesn't want to replace crontab in its day to day usefulness but it does want to provide some advantages in certain situations like: integration in the language, easy to use APIs, programmble capabilities, optional job parallelism execution

Install

go get github.com/damdo/grontab

Note that the vendor folder is here for stability. Remove the folder if you already have the dependencies in your GOPATH.

Usage

tl;dr;

package main

import (
        "log"
        "os"
        "os/signal"
        "github.com/damdo/grontab"
)

func main() {
    // create a new grontab configuration
    newConfig := grontab.Config{
            BucketName:         "jobs",
            PersistencePath:    "./db.db",
            DisableParallelism: false,
            HideBanner:         false,
            TurnOffLogs:        false,
    }

    // initialize grontab with the new configuration
    err := grontab.Init(newConfig)
    if err != nil {
            log.Fatal(err)
    }

    // create a new grontab job
    newJob := grontab.Job{Task: "ping -c 4 8.8.8.8", Enabled: true}

    // a new grontab job to be executed at the specified schedule
    idPing, err := grontab.Add("00 00 06 * * *", newJob)
    if err != nil {
            log.Println(err)
    }

    // start grontab
    grontab.Start()

    // update the existing idPing job with a new schedule and a new command task
    err = grontab.Update("*/10 * * * * *", grontab.Job{ID: idPing, Task: "echo 'ciaone'", Enabled: true})
    if err != nil {
    	log.Println(err)
    }

    // // optionally remove the existing job
    // err = grontab.Remove(idPing)
    // if err != nil {
    //     log.Println(err)
    // }

    // this is needed to keep awake the execution
    sig := make(chan os.Signal)
    signal.Notify(sig, os.Interrupt, os.Kill)
    <-sig
}

1) import

The first step is to import the package

import(
    "github.com/damdo/grontab"
)

2) grontab.Init()

Then grontab has to be initialized, with the Init() command, specifing the desired configuration. Boolean parameters have default value to false. The configuration lives in a grontab.Config that takes various parameters:

• PersistencePath: will be the path of the storage file
• BucketName: will be the data collection name
• DisableParallelism: allow to choose if jobs at the same schedule will run in parallel or sequentially
• HideBanner: allow to choose if the grontab banner will be shown at runtime
• TurnOffLogs: allow to choose if the grontab logs will be shown at runtime

Once the config is defined, it should be passed to Init() to complete the initialization

newConfig := grontab.Config{
    BucketName: "jobs",
    PersistencePath: "./db.db",
    DisableParallelism: false,
    HideBanner: false,
    TurnOffLogs: false,
}

err := grontab.Init(newConfig)

if err != nil {
    log.Fatal(err)
}

3) grontab.Start()

The next step can be to spin up the grontab engine to start processing the schedule. Start(), however, can be invoked at anytime, even after the Add()'s commands, provided that grontab as been Initialized.

grontab.Start()

4) grontab.Add()

One of the possibilities after the Init() (and optionally after Start()) is the Add() command. This command is meant to be used to add a new entry in grontab, a new schedule. It takes as parameters:

1. a crontab like schedule string, syntax here
2. a grontab.Job which takes:
   • Task: a unix command string
   • Enabled: a true/false boolean flag to enable/disable the execution of the task

newJob := grontab.Job{Task: "ping -c 4 8.8.8.8", Enabled: true}
idPing, err := grontab.Add("00 00 06 * * *", newJob)

if err != nil {
    log.Println(err)
}
log.Println(idPing)

5) grontab.Update()

One of the possibilities after the Init() (and optionally after Start()) is the Update() command. This command is meant to be used to update tasks already present in grontab. It takes as parameters:

1. optionally an updated crontab like schedule string, syntax here
2. a grontab.Job which takes:
   • ID: the id of the job to be updated string (MANDATORY)
   • Task: the updated unix command string (OPTIONAL)
   • Enabled: the updated true/false boolean flag to enable/disable the execution of the task (OPTIONAL)

newJob := grontab.Job{Task: "ping -c 4 8.8.8.8", Enabled: true}
idPing, err := grontab.Add("00 00 06 * * *", newJob)
if err != nil {
    log.Println(err)
}

// VALID
// in this case both the schedule and the command/task of the job will be updated
err = grontab.Update("00 10 07 * 1 *", grontab.Job{ID: idPing, Task: "echo 'ciaone'", Enabled: true})
if err != nil {
	log.Println(err)
}

// VALID
// in this case the schedule of the job will be updated
err = grontab.Update("00 12 08 * 1 *", grontab.Job{ID: idPing})
if err != nil {
	log.Println(err)
}

// VALID
// in this case the schedule of the job and the Enabled status will be updated
err = grontab.Update("00 12 08 * 1 *", grontab.Job{ID: idPing, Enabled: false})
if err != nil {
	log.Println(err)
}

// INVALID
// the Update is invalid because the job ID is missing
err = grontab.Update("00 12 08 * 1 *", grontab.Job{Enabled: false})
if err != nil {
	log.Println(err)
}

6) grontab.Remove()

One of the possibilities after the Init() (and optionally after Start()) is the Remove() command. This command is meant to be used to remove an entry in grontab. It takes as parameter:

1. ID of the job to be removed

newJob := grontab.Job{Task: "ping -c 4 8.8.8.8", Enabled: true}
idPing, err := grontab.Add("00 00 06 * * *", newJob)
if err != nil {
    log.Println(err)
}

err := grontab.Remove(idPing)
if err != nil {
    log.Println(err)
}

7) grontab.Stop()

The Stop() command is meant to be used to stop the started grontab engine. It should be run only after Init() and Start() have been invoked.

grontab.Stop()

8) grontab.List()

The List() command is meant to be used to list the schedules and jobs already in the grontab engine. It should be run only after Init() have been invoked.

occurrencies := grontab.List()

Credits

• @asdine for github.com/asdine/storm
• @etcd-io for github.com/etcd-io/bbolt
• @damdo for github.com/damdo/randid
• @fatih for github.com/fatih/color
• @davecheney for github.com/pkg/errors
• @robfig and @wgliang for github.com/wgliang/cron

License

• This project uses third party libraries that are distributed under their own terms. See 3RD-PARTY
• For the rest of it the MIT License (MIT) applies. See LICENSE for more details