Docker Container Cron Alternative With Jobber.

AWS = Amazon Web Services, GCE = Google Cloud Engine

blacklabelops/cron-cloud

In short, you can define periodic tasks for an arbitrary number of jobs.

Example:

$ docker run -d \
    --name jobber \
    -e "JOB_NAME1=TestEcho" \
    -e "JOB_COMMAND1=echo hello world" \
    blacklabelops/jobber

Will print "hello world" to console every second.

The environment variables are numerated. Just add the number behind the environment variable and the container will create a job definition for Jobber!

This way the container can handle an arbitrary number of jobs without file handling or cumbersome syntax!

Example with two tasks:

$ docker run -d \
    --name jobber \
    -e "JOB_NAME1=TestEcho" \
    -e "JOB_COMMAND1=echo hello world" \
    -e "JOB_NAME2=TestEcho" \
    -e "JOB_COMMAND2=echo hello moon" \
    blacklabelops/jobber

First job will print "hello world" and then second job will print "hello moon" to console every second.

Every job definition is specified by up to four environment variables:

• JOB_NAME: The identifier for the job, must not contain empty spaces!
• JOB_COMMAND: The bash command to be executed.
• JOB_TIME: The cron schedule for the job. See Documentation
• JOB_ON_ERROR: How Jobber should act on errors. Values: Stop, Backoff, Continue (Default). See Documentation

Full example:

$ docker run -d \
    --name jobber \
    -e "JOB_NAME1=TestEcho" \
    -e "JOB_COMMAND1=echo hello world" \
    -e "JOB_TIME1=1" \
    -e "JOB_ON_ERROR1=Backoff" \
    blacklabelops/jobber

Will print "hello world" in 1 second of every minute.

When it comes to the cron string then Jobber is a little bit different. If you do not define any time then the resulting cron table will be

* * * * * *

and the job will be executed every second.

You can also define just one number "1". This will be interpreted as

1 * * * * *

so you can see that you have to specify the time string from the back and the rest will be filled up by Jobber.

As a reminder, cron timetable is like follows:

1. Token: Second
2. Token: Minute
3. Token: Hour
4. Token: Day of Month
5. Token: Month
6. Token: Day of Week

Vagrant is fabulous tool for pulling and spinning up virtual machines like docker with containers. I can configure my development and test environment and simply pull it online. And so can you! Install Vagrant and Virtualbox and spin it up. Change into the project folder and build the project on the spot!

$ vagrant up
$ vagrant ssh
[vagrant@localhost ~]$ cd /vagrant
[vagrant@localhost ~]$ docker-compose up

Type "docker logs jobber" in order to check the invocation.

Vagrant does not leave any docker artifacts on your beloved desktop and the vagrant image can simply be destroyed and repulled if anything goes wrong. Test my project to your heart's content!

First install:

• Vagrant
• Virtualbox

• Jobber
• Docker Homepage
• Docker Userguide