Learn how to submit jobs to Nomad

In Nomad, the description of the job and all its requirements are maintained in a single file called the "job file". This job file resides locally on disk and it is highly recommended that you check job files into source control.

The general flow for submitting a job in Nomad is:

1. Author a job file according to the job specification
2. Plan and review changes with a Nomad server
3. Submit the job file to a Nomad server
4. (Optional) Review job status and logs

Here is a very basic example to get you started.

Author a job file

Nomad attempts to strike a balance between ease and expressiveness in its job specification. Nomad also provides the nomad init command to generate sample job files. For more detailed information about the Nomad job specification, please consult the Nomad documentation.

Here is a sample job file which runs a small docker container web server to start with.

job "docs" {  datacenters = ["dc1"]   group "example" {    network {      port "http" {        static = "5678"      }    }    task "server" {      driver = "docker"       config {        image = "hashicorp/http-echo"        ports = ["http"]        args = [          "-listen",          ":5678",          "-text",          "hello world",        ]      }    }  }}

This job file exists on your local workstation in plain text. When you are satisfied with this job file, you will plan and review the scheduler decision. It is generally a best practice to commit job files to source control, especially if you are working in a team.

Plan the job

Once the job file is authored, you probably want to preview the changes Nomad will make when it runs. The nomad job plan command invokes a dry-run of the scheduler and output which scheduling decisions would take place.

$ nomad job plan docs.nomad.hcl+ Job: "docs"+ Task Group: "example" (1 create)  + Task: "server" (forces create) Scheduler dry-run:- All tasks successfully allocated. Job Modify Index: 0To submit the job with version verification run: nomad job run -check-index 0 docs.nomad.hcl When running the job with the check-index flag, the job will only be run if thejob modify index given matches the server-side version. If the index haschanged, another user has modified the job and the plan's results arepotentially invalid.

Note that no action was taken. This job is not running. This is a complete dry-run and no allocations have taken place.

Submit the job

Assuming the output of the plan looks acceptable, now ask Nomad to execute the job. This is done via the nomad job run command. You can optionally supply the modify index provided by the plan command to ensure no changes to this job have taken place between our plan and now.

$ nomad job run docs.nomad.hcl==> Monitoring evaluation "0d159869"    Evaluation triggered by job "docs"    Allocation "5cbf23a1" created: node "1e1aa1e0", group "example"    Evaluation status changed: "pending" -> "complete"==> Evaluation "0d159869" finished with status "complete"

Now that the job is scheduled, it may or may not be running. You need to inspect the allocation status and logs to make sure the job started correctly. The next section on inspecting state details ways to examine this job's state.

Update and plan the job

When making updates to the job, it is best to always run the plan command and then the run command. For example:

@@ -2,6 +2,8 @@ job "docs" {   datacenters = ["dc1"]    group "example" {+    count = "2"+     task "server" {       driver = "docker"

After saving these changes to disk, run the nomad job plan command:

$ nomad job plan docs.nomad.hcl+/- Job: "docs"+/- Task Group: "example" (1 create, 1 in-place update)  +/- Count: "1" => "2" (forces create)      Task: "server" Scheduler dry-run:- All tasks successfully allocated. Job Modify Index: 131To submit the job with version verification run: nomad job run -check-index 131 docs.nomad.hcl When running the job with the check-index flag, the job will only be run if thejob modify index given matches the server-side version. If the index haschanged, another user has modified the job and the plan's results arepotentially invalid.

Reserved port collisions

Because this job uses a static port, it is possible for some instances to not be placeable depending on the number of clients you have in your Nomad cluster. If your plan output contains:

Dimension "network: reserved port collision" exhausted on x nodes

This indicates that every feasible client in your cluster has or will have something placed at the requested port, leaving no place for some of these allocations to run. To resolve this, you need to reduce the requested count, add additional clients, or migrate from static ports to dynamic ports in your job specification.

Run the job

Now, assuming the output is okay, execute the nomad job run command. Including the check-index parameter ensures that the job was not changed between the plan and run phases.

$ nomad job run -check-index 131 docs.nomad.hcl==> Monitoring evaluation "42d788a3"    Evaluation triggered by job "docs"    Allocation "e7b8d4f5" created: node "012ea79b", group "example"    Allocation "5cbf23a1" modified: node "1e1aa1e0", group "example"    Evaluation status changed: "pending" -> "complete"==> Evaluation "42d788a3" finished with status "complete"

For more details on advanced job updating strategies such as canary builds and build-green deployments, consult the documentation on job update strategies.