--- layout: intro page_title: Jobs sidebar_title: Jobs description: '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 in the [job specification][jobspec]. They can either be specified in [HashiCorp Configuration Language][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 [`job init` command](/docs/commands/job/init) which generates a skeleton job file: ```shell-session $ nomad job init Example job file written to example.nomad ``` You can view the contents of this file by running `cat example.nomad`. 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 [`job run` command](/docs/commands/job/run). 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: ```shell-session $ nomad job run example.nomad ==> Monitoring evaluation "13ebb66d" Evaluation triggered by job "example" Allocation "883269bf" created: node "e42d6f19", group "cache" Evaluation within deployment: "b0a84e74" Evaluation status changed: "pending" -> "complete" ==> Evaluation "13ebb66d" 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](/docs/commands/status): ```shell-session $ nomad status example ID = example Name = example Submit Date = 10/31/17 22:58:40 UTC Type = service Priority = 50 Datacenters = dc1 Status = running Periodic = false Parameterized = false Summary Task Group Queued Starting Running Failed Complete Lost cache 0 0 1 0 0 0 Latest Deployment ID = b0a84e74 Status = successful Description = Deployment completed successfully Deployed Task Group Desired Placed Healthy Unhealthy cache 1 1 1 0 Allocations ID Node ID Task Group Version Desired Status Created Modified 8ba85cef 171a583b cache 0 run running 5m ago 5m ago ``` Here we can see that the result of our evaluation was the creation of an allocation that is now running on the local node. An allocation represents an instance of Task Group placed on a node. To inspect an allocation we use the [`alloc status` command](/docs/commands/alloc/status): ```shell-session $ nomad alloc status 8ba85cef ID = 8ba85cef Eval ID = 13ebb66d Name = example.cache[0] Node ID = e42d6f19 Job ID = example Job Version = 0 Client Status = running Client Description = Desired Status = run Desired Description = Created = 5m ago Modified = 5m ago Deployment ID = fa882a5b Deployment Health = healthy Task "redis" is "running" Task Resources CPU Memory Disk Addresses 8/500 MHz 6.3 MiB/256 MiB 300 MiB db: 127.0.0.1:22672 Task Events: Started At = 10/31/17 22:58:49 UTC Finished At = N/A Total Restarts = 0 Last Restart = N/A Recent Events: Time Type Description 10/31/17 22:58:49 UTC Started Task started by client 10/31/17 22:58:40 UTC Driver Downloading image redis:3.2 10/31/17 22:58:40 UTC Task Setup Building Task Directory 10/31/17 22:58:40 UTC Received Task received by client ``` We can see that Nomad reports the state of the allocation as well as its current resource usage. By supplying the `-stats` flag, more detailed resource usage statistics will be reported. To see the logs of a task, we can use the [`logs` command](/docs/commands/alloc/logs): ````shell-session $ nomad alloc logs 8ba85cef redis _._ _.-``__ ''-._ _.-`` `. `_. ''-._ Redis 3.2.1 (00000000/0) 64 bit .-`` .-```. ```\/ _.,_ ''-._ ( ' , .-` | `, ) Running in standalone mode |`-._`-...-` __...-.``-._|'` _.-'| Port: 6379 | `-._ `._ / _.-' | PID: 1 `-._ `-._ `-./ _.-' _.-' |`-._`-._ `-.__.-' _.-'_.-'| | `-._`-._ _.-'_.-' | http://redis.io `-._ `-._`-.__.-'_.-' _.-' |`-._`-._ `-.__.-' _.-'_.-'| | `-._`-._ _.-'_.-' | `-._ `-._`-.__.-'_.-' _.-' `-._ `-.__.-' _.-' `-._ _.-' `-.__.-' ... ```` ## 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 update the count and set it to 3: ``` # The "count" parameter specifies the number of the task groups that should # be running under this group. This value must be non-negative and defaults # to 1. count = 3 ``` Once you have finished modifying the job specification, use the [`job plan` command](/docs/commands/job/plan) to invoke a dry-run of the scheduler to see what would happen if you ran the updated job: ```shell-session $ nomad job plan example.nomad +/- Job: "example" +/- Task Group: "cache" (2 create, 1 in-place update) +/- Count: "1" => "3" (forces create) Task: "redis" Scheduler dry-run: - All tasks successfully allocated. Job Modify Index: 7 To submit the job with version verification run: nomad job run -check-index 7 example.nomad When running the job with the check-index flag, the job will only be run if the job modify index given matches the server-side version. If the index has changed, another user has modified the job and the plan's results are potentially invalid. ``` We can see that the scheduler detected the change in count and informs us that it will cause 2 new instances to be created. The in-place update that will occur is to push the updated job specification to the existing allocation and will not cause any service interruption. We can then run the job with the run command the `plan` emitted. By running with the `-check-index` flag, Nomad checks that the job has not been modified since the plan was run. This is useful if multiple people are interacting with the job at the same time to ensure the job hasn't changed before you apply your modifications. ```shell-session $ nomad job run -check-index 7 example.nomad ==> Monitoring evaluation "93d16471" Evaluation triggered by job "example" Evaluation within deployment: "0d06e1b6" Allocation "3249e320" created: node "e42d6f19", group "cache" Allocation "453b210f" created: node "e42d6f19", group "cache" Allocation "883269bf" modified: node "e42d6f19", group "cache" Evaluation status changed: "pending" -> "complete" ==> Evaluation "93d16471" 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:3.2" to "redis:4.0": ``` # Configure Docker driver with the image config { image = "redis:4.0" } ``` We can run `plan` again to see what will happen if we submit this change: ```text +/- Job: "example" +/- Task Group: "cache" (1 create/destroy update, 2 ignore) +/- Task: "redis" (forces create/destroy update) +/- Config { +/- image: "redis:3.2" => "redis:4.0" port_map[0][db]: "6379" } Scheduler dry-run: - All tasks successfully allocated. Job Modify Index: 1127 To submit the job with version verification run: nomad job run -check-index 1127 example.nomad When running the job with the check-index flag, the job will only be run if the job modify index given matches the server-side version. If the index has changed, another user has modified the job and the plan's results are potentially invalid. ``` The plan output shows us that one allocation will be updated and that the other two will be ignored. This is due to the `max_parallel` setting in the `update` stanza, which is set to 1 to instruct Nomad to perform only a single change at a time. Once ready, use `run` to push the updated specification: ```shell-session $ nomad job run example.nomad ==> Monitoring evaluation "293b313a" Evaluation triggered by job "example" Evaluation within deployment: "f4047b3a" Allocation "27bd4a41" created: node "e42d6f19", group "cache" Evaluation status changed: "pending" -> "complete" ==> Evaluation "293b313a" finished with status "complete" ``` After running, the rolling upgrade can be followed by running `nomad status` and watching the deployed count. We can see that Nomad handled the update in three phases, only updating a single allocation in each phase and waiting for it to be healthy for `min_healthy_time` of 10 seconds before moving on to the next. 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 [`job stop` command](/docs/commands/job/stop): ```shell-session $ nomad job stop example ==> Monitoring evaluation "6d4cd6ca" Evaluation triggered by job "example" Evaluation within deployment: "f4047b3a" Evaluation status changed: "pending" -> "complete" ==> Evaluation "6d4cd6ca" finished with status "complete" ``` When we stop a job, it creates an evaluation which is used to stop all the existing allocations. If we now query the job status, we can see it is now marked as `dead (stopped)`, indicating that the job has been stopped and Nomad is no longer running it: ```shell-session $ nomad status example ID = example Name = example Submit Date = 11/01/17 17:30:40 UTC Type = service Priority = 50 Datacenters = dc1 Status = dead (stopped) Periodic = false Parameterized = false Summary Task Group Queued Starting Running Failed Complete Lost cache 0 0 0 0 6 0 Latest Deployment ID = f4047b3a Status = successful Description = Deployment completed successfully Deployed Task Group Desired Placed Healthy Unhealthy cache 3 3 3 0 Allocations ID Node ID Task Group Version Desired Status Created Modified 8ace140d 2cfe061e cache 2 stop complete 5m ago 5m ago 8af5330a 2cfe061e cache 2 stop complete 6m ago 6m ago df50c3ae 2cfe061e cache 2 stop complete 6m ago 6m ago ``` 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](/intro/getting-started/cluster) [jobspec]: /docs/job-specification 'Nomad Job Specification' [hcl]: https://github.com/hashicorp/hcl 'HashiCorp Configuration Language'