open-nomad/website/source/intro/getting-started/jobs.html.md

layout	page_title	sidebar_current	description
intro	Jobs	getting-started-jobs	Learn how to submit, modify and stop jobs in Nomad.

Jobs

Jobs are the primary configuration that users interact with when using Nomad. A job is a declarative specification of tasks that Nomad should run. Jobs have a globally unique name, one or many task groups, which are themselves collections of one or many tasks.

The format of the jobs is documented here. They can either be specified in HCL or JSON, however we recommend only using JSON when the configuration is generated by a machine.

Running a Job

To get started, we will use the init command which generates a skeleton job file:

$ nomad init
Example job file written to example.nomad

$ cat example.nomad

# There can only be a single job definition per file.
# Create a job with ID and Name 'example'
job "example" {
	# Run the job in the global region, which is the default.
	# region = "global"
...

In this example job file, we have declared a single task 'redis' which is using the Docker driver to run the task. The primary way you interact with Nomad is with the run command. The run command takes a job file and registers it with Nomad. This is used both to register new jobs and to update existing jobs.

We can register our example job now:

$ nomad run example.nomad
==> Monitoring evaluation "26cfc69e"
    Evaluation triggered by job "example"
    Allocation "8ba85cef" created: node "171a583b", group "cache"
    Evaluation status changed: "pending" -> "complete"
==> Evaluation "26cfc69e" finished with status "complete"

Anytime a job is updated, Nomad creates an evaluation to determine what actions need to take place. In this case, because this is a new job, Nomad has determined that an allocation should be created and has scheduled it on our local agent.

To inspect the status of our job we use the status command:

$ nomad status example
ID          = example
Name        = example
Type        = service
Priority    = 50
Datacenters = dc1
Status      = running
Periodic    = false

==> Evaluations
ID        Priority  Triggered By  Status
26cfc69e  50        job-register  complete

==> Allocations
ID        Eval ID   Node ID   Task Group  Desired  Status
8ba85cef  26cfc69e  171a583b  cache       run      running

Here we can see that our evaluation that was created has completed, and that it resulted in the creation of an allocation that is now running on the local node.

Modifying a Job

The definition of a job is not static, and is meant to be updated over time. You may update a job to change the docker container, to update the application version, or to change the count of a task group to scale with load.

For now, edit the example.nomad file to uncomment the count and set it to 3:

# Control the number of instances of this group.
# Defaults to 1
count = 3

Once you have finished modifying the job specification, use nomad run to push the updated version of the job:

$ nomad run example.nomad
==> Monitoring evaluation "127a49d0"
    Evaluation triggered by job "example"
    Allocation "8ab24eef" created: node "171a583b", group "cache"
    Allocation "f6c29874" created: node "171a583b", group "cache"
    Allocation "8ba85cef" modified: node "171a583b", group "cache"
    Evaluation status changed: "pending" -> "complete"
==> Evaluation "127a49d0" finished with status "complete"

Because we set the count of the task group to three, Nomad created two additional allocations to get to the desired state. It is idempotent to run the same job specification again and no new allocations will be created.

Now, let's try to do an application update. In this case, we will simply change the version of redis we want to run. Edit the example.nomad file and change the Docker image from "redis:latest" to "redis:2.8":

# Configure Docker driver with the image
config {
    image = "redis:2.8"
}

This time we have not changed the number of task groups we want running, but we've changed the task itself. This requires stopping the old tasks and starting new tasks. Our example job is configured to do a rolling update via the stagger attribute, doing a single update every 10 seconds. Use run to push the updated specification now:

$ nomad run example.nomad
==> Monitoring evaluation "ebcc3e14"
    Evaluation triggered by job "example"
    Allocation "9a3743f4" created: node "171a583b", group "cache"
    Evaluation status changed: "pending" -> "complete"
==> Evaluation "ebcc3e14" finished with status "complete"
==> Monitoring evaluation "b508d8f0"
    Evaluation triggered by job "example"
    Allocation "926e5876" created: node "171a583b", group "cache"
    Evaluation status changed: "pending" -> "complete"
==> Evaluation "b508d8f0" finished with status "complete"
==> Monitoring next evaluation "ea78c05a" in 10s
==> Monitoring evaluation "ea78c05a"
    Evaluation triggered by job "example"
    Allocation "3c8589d5" created: node "171a583b", group "cache"
    Evaluation status changed: "pending" -> "complete"
==> Evaluation "ea78c05a" finished with status "complete"

We can see that Nomad handled the update in three phases, only updating a single task group in each phase. The update strategy can be configured, but rolling updates makes it easy to upgrade an application at large scale.

Stopping a Job

So far we've created, run and modified a job. The final step in a job lifecycle is stopping the job. This is done with the stop command:

$ nomad stop example
==> Monitoring evaluation "fd03c9f8"
    Evaluation triggered by job "example"
    Evaluation status changed: "pending" -> "complete"
==> Evaluation "fd03c9f8" finished with status "complete"

When we stop a job, it creates an evaluation which is used to stop all the existing allocations. This also deletes the job definition out of Nomad. If we try to query the job status, we can see it is no longer registered:

$ nomad status example
No job(s) with prefix or id "example" found

If we wanted to start the job again, we could simply run it again.

Next Steps

Users of Nomad primarily interact with jobs, and we've now seen how to create and scale our job, perform an application update, and do a job tear down. Next we will add another Nomad client to create our first cluster