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| 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 "3d823c52-929a-fa8b-c50d-1ac4d00cf6b7"
Evaluation triggered by job "example"
Allocation "85b839d7-f67a-72a4-5a13-104020ae4807" created: node "2512929f-5b7c-a959-dfd9-bf8a8eb022a6", group "cache"
Evaluation status changed: "pending" -> "complete"
==> Evaluation "3d823c52-929a-fa8b-c50d-1ac4d00cf6b7" 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 = <none>
==> Evaluations
ID Priority TriggeredBy Status
3d823c52-929a-fa8b-c50d-1ac4d00cf6b7 50 job-register complete
==> Allocations
ID EvalID NodeID TaskGroup Desired Status
85b839d7-f67a-72a4-5a13-104020ae4807 3d823c52-929a-fa8b-c50d-1ac4d00cf6b7 2512929f-5b7c-a959-dfd9-bf8a8eb022a6 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 groups.
# 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 "ec199c63-2022-f5c7-328d-1cf85e61bf66"
Evaluation triggered by job "example"
Allocation "21551679-5224-cb6b-80a2-d0b091612d2e" created: node "2512929f-5b7c-a959-dfd9-bf8a8eb022a6", group "cache"
Allocation "b1be1410-a01c-20ad-80ff-96750ec0f1da" created: node "2512929f-5b7c-a959-dfd9-bf8a8eb022a6", group "cache"
Allocation "ed32a35d-8086-3f04-e299-4432e562cbf2" created: node "2512929f-5b7c-a959-dfd9-bf8a8eb022a6", group "cache"
Evaluation status changed: "pending" -> "complete"
==> Evaluation "ec199c63-2022-f5c7-328d-1cf85e61bf66" 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, lets 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 "d34d37f4-19b1-f4c0-b2da-c949e6ade82d"
Evaluation triggered by job "example"
Allocation "5614feb0-212d-21e5-ccfb-56a394fc41d5" created: node "2512929f-5b7c-a959-dfd9-bf8a8eb022a6", group "cache"
Allocation "bf7e3ad5-b217-14fe-f3f8-2b83af9dbb42" created: node "2512929f-5b7c-a959-dfd9-bf8a8eb022a6", group "cache"
Allocation "e3978af2-f61e-c601-7aa1-90aea9b23cf6" created: node "2512929f-5b7c-a959-dfd9-bf8a8eb022a6", group "cache"
Evaluation status changed: "pending" -> "complete"
==> Evaluation "d34d37f4-19b1-f4c0-b2da-c949e6ade82d" finished with status "complete"
We can see that Nomad handled the updated in three phases, each time only updating a single task group at a time. 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 "bb407de4-02cb-f009-d986-646d6c11366d"
Evaluation triggered by job "example"
Evaluation status changed: "pending" -> "complete"
==> Evaluation "bb407de4-02cb-f009-d986-646d6c11366d" 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
Error querying job: Unexpected response code: 404 (job not 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