chronos

How to use Chronos on DC/OS

Note: DC/OS now includes a built-in job scheduler, which is the preferable way to schedule batch jobs.

Chronos is still available on DC/OS, representing the original way to run batch jobs. It is a highly-available, distributed job scheduler, providing the a robust way to run batch jobs. Chronos schedules jobs across the DC/OS cluster and manages dependencies between jobs in an intelligent way.

• Estimated time for completion: 15 minutes
• Target audience:
• Data engineers
• Data scientists
• DevOps engineers
• Scope: Setup and usage of a batch scheduler for DC/OS.

Table of Contents:

• Prerequisites
• Install Chronos
• Create a scheduled job
• Uninstall Chronos

Prerequisites

• A running DC/OS 1.8 cluster with 1 nodes with at least 2GB of RAM and 1 CPU available in the cluster.
• DC/OS CLI installed.

Install Chronos

From the command line, enter this command:

$ dcos package install chronos
We recommend a minimum of one node with at least 1 CPU and 2GB of RAM available for the Chronos Service.
Continue installing? [yes/no] yes
Installing Marathon app for package [chronos] version [2.4.0]
Chronos DCOS Service has been successfully installed!

	Documentation: http://mesos.github.io/chronos
	Issues: https://github.com/mesos/chronos/issues

Note that you can specify a JSON configuration file along with the Chronos installation command to customize the setup, like so: dcos package install chronos --options=<config_file>. For more information, see the DC/OS CLI command reference.

Next, validate that Chronos is successfully installed. Go to the Services tab of the DC/OS UI and check if Chronos shows up in the list as Healthy:

In addition, run this command to view installed services:

$ dcos package list
NAME        VERSION  APP       COMMAND     DESCRIPTION
chronos     2.4.0    /chronos  ---         A fault tolerant job scheduler for Mesos which handles dependencies and ISO8601 based schedules.

Create a scheduled job

Open the Chronos UI from the DC/OS UI via the Open Service button and click the New Job link to bring up the form for creating jobs.

Next, fill in the following values in the form:

• NAME: "Date"
• DESCRIPTION: "Prints the current date"
• COMMAND: /bin/date
• OWNER(S): Enter your email address.
• SCHEDULE: Enter T10S in the P field

Note that Chronos uses ISO 8601 Interval Notation to describe job schedules, so T10S means run this job every 10 seconds.

Now click the Create button at the top of the form to submit the job.

Let's verify that our job ran successfully. Run the following CLI command to view all completed tasks:

$ dcos task --completed ct*
NAME              HOST        USER  STATE  ID
ChronosTask:Date  10.0.3.226  root    F    ct:1478092145000:0:Date:
ChronosTask:Date  10.0.3.229  root    F    ct:1478092135000:0:Date:
ChronosTask:Date  10.0.3.230  root    F    ct:1478091935000:0:Date:

Note that the --completed argument includes tasks that have completed their execution. Chronos uses the prefix ct for all its tasks, so ct* filters out Chronos tasks.

To view the output of a task, copy one of the values under the ID column in the output of the previous command and use it as the argument to dcos task log:

$ dcos task log --completed ct:1478092145000:0:Date:
Executing pre-exec command '{"arguments":["mesos-containerizer","mount","--help=false","--operation=make-rslave","--path=\/"],"shell":false,"value":"\/opt\/mesosphere\/packages\/mesos--55e36b7783f1549d26b7567b11090ff93b89487a\/libexec\/mesos\/mesos-containerizer"}'
Received SUBSCRIBED event
Subscribed executor on 10.0.3.226
Received LAUNCH event
Starting task ct:1478092145000:0:Date:
/opt/mesosphere/packages/mesos--55e36b7783f1549d26b7567b11090ff93b89487a/libexec/mesos/mesos-containerizer launch --command="{"environment":{"variables":[{"name":"mesos_task_id","value":"ct:1478092145000:0:Date:"},{"name":"CHRONOS_JOB_OWNER","value":"michael@dcos.io"},{"name":"CHRONOS_JOB_NAME","value":"Date"},{"name":"HOST","value":"10.0.3.226"},{"name":"CHRONOS_RESOURCE_MEM","value":"128.0"},{"name":"CHRONOS_RESOURCE_CPU","value":"0.1"},{"name":"CHRONOS_RESOURCE_DISK","value":"256.0"}]},"shell":true,"user":"root","value":"\/bin\/date"}" --help="false" --unshare_namespace_mnt="false"
Forked command at 7835
Wed Nov  2 13:09:06 UTC 2016
Command exited with status 0 (pid: 7835)

You can also see the status of the job you entered in the Chronos UI:

Uninstall Chronos

To uninstall Chronos enter the following command:

$ dcos package uninstall chronos

Finally, to get rid of all traces of Chronos in ZooKeeper, follow the steps outlined in the framework cleaner.