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Alex Dadgar 1b6e772681 JSON page docs
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docs JSON Job Specification docs-jobspec-json-syntax Learn about the Job specification used to submit jobs to Nomad in JSON.

Job Specification

Jobs can be specified either in HCL or JSON. This guide covers the json syntax for submitting jobs to Nomad. A useful command for generating valid JSON versions of HCL jobs is nomad run -output <job.nomad> which will emit a JSON version of the job.

JSON Syntax

Below is an example of a json object that submits a Periodic job to Nomad:

{
"Job": {
      "Datacenters": [
        "dc1"
      ],
      "ID": "example1",
      "AllAtOnce": false,
      "Priority": 50,
      "Type": "batch",
      "Name": "example1",
      "Region": "global",
      "Constraints": [
        {
          "Operand": "=",
          "RTarget": "linux",
          "LTarget": "${attr.kernel.name}"
        }
      ],
      "TaskGroups": [
        {
          "Meta": null,
          "Tasks": [
            {
              "LogConfig": {
                "MaxFileSizeMB": 10,
                "MaxFiles": 10
              },
              "KillTimeout": 5000000000,
              "Name": "redis",
              "Driver": "docker",
              "Config": {
                "Command": "/bin/date",
                "port_map": [
                  {
                    "db": 6379
                  }
                ],
                "image": "redis:latest"
              },
              "Env": {
                  "foo": "bar"
              },
              "Services": [
                {
                  "Checks": [
                    {
                      "Timeout": 2000000000,
                      "Interval": 10000000000,
                      "Protocol": "",
                      "Path": "",
                      "Script": "",
                      "Type": "tcp",
                      "Name": "alive"
                    }
                  ],
                  "PortLabel": "db",
                  "Tags": [
                    "global",
                    "cache"
                  ],
                  "Name": "cache-redis"
                }
              ],
              "Constraints": null,
              "Resources": {
                "Networks": [
                  {
                    "DynamicPorts": [
                      {
                        "Value": 0,
                        "Label": "db"
                      }
                    ],
                  }
                ],
                "IOPS": 0,
                "DiskMB": 300,
                "MemoryMB": 256,
                "CPU": 500
              },
              "Meta": {
                  "foo": "bar",
                  "baz": "pipe"
              }
            }
          ],
          "RestartPolicy": {
            "Mode": "delay",
            "Delay": 25000000000,
            "Interval": 300000000000,
            "Attempts": 10
          },
          "Constraints": null,
          "Count": 1,
          "Name": "cache"
        }
      ],
      "Update": {
        "MaxParallel": 1,
        "Stagger": 10000000000
      },
      "Periodic": {
          "Enabled": true,
          "Spec": "* * * * *",
          "SpecType": "cron",
          "ProhibitOverlap": true
      },
      "Meta": {
          "foo": "bar",
          "baz": "pipe"
      }
    }
}

Syntax Reference

Following is a syntax reference for the possible keys that are supported and their default values if any for each type of object.

Job

The Job object supports the following keys:

  • AllAtOnce - Controls if the entire set of tasks in the job must be placed atomically or if they can be scheduled incrementally. This should only be used for special circumstances. Defaults to false.

  • Constraints - A list to define additional constraints where a job can be run. See the constraint reference for more details.

  • Datacenters - A list of datacenters in the region which are eligible for task placement. This must be provided, and does not have a default.

  • TaskGroups - A list to define additional task groups. See the task group reference for more details.

  • Meta - Annotates the job with opaque metadata.

  • Priority - Specifies the job priority which is used to prioritize scheduling and access to resources. Must be between 1 and 100 inclusively, and defaults to 50.

  • Region - The region to run the job in, defaults to "global".

  • Type - Specifies the job type and switches which scheduler is used. Nomad provides the service, system and batch schedulers, and defaults to service. To learn more about each scheduler type visit here

  • Update - Specifies the task's update strategy. When omitted, rolling updates are disabled. The Update object supports the following attributes:

    • MaxParallel - MaxParallel is given as an integer value and specifies the number of tasks that can be updated at the same time.

    • Stagger - Stagger introduces a delay between sets of task updates and is given as an as a time duration. The value of stagger has to be in nanoseconds.

    An example update block:

    "Update": {
    "MaxParallel" : 3,
    "Stagger" : 300000000
}

  • Periodic - Periodic allows the job to be scheduled at fixed times, dates or intervals. The Periodic object supports the following attributes:

    • Enabled - Enabled determines whether the periodic job will spawn child jobs.

    • SpecType - SpecType determines how Nomad is going to interpret the periodic expression. cron is the only supported SpecType currently.

    • Spec - A cron expression configuring the interval the job is launched at. Supports predefined expressions such as "@daily" and "@weekly" See here for full documentation of supported cron specs and the predefined expressions.

    • ProhibitOverlap - ProhibitOverlap can be set to true to enforce that the periodic job doesn't spawn a new instance of the job if any of the previous jobs are still running. It is defaulted to false.

    An example periodic block:

        "Periodic": {
        "Spec": "*/15 * * * * *"
        "SpecType": "cron",
        "Enabled": true,
        "ProhibitOverlap": true
    }

Task Group

TaskGroups is a list of Task Group, and each object supports the following attributes:

  • Count - Specifies the number of the task groups that should be running. Must be positive, defaults to one.

  • Constraints - This is a list of Constraint objects. See the constraint reference for more details.

  • RestartPolicy - Specifies the restart policy to be applied to tasks in this group. If omitted, a default policy for batch and non-batch jobs is used based on the job type. See the restart policy reference for more details.

  • Tasks - It's a list of Task object, allows adding tasks as part of the group.

  • Meta - Annotates the task group with opaque metadata.

Task

The Task object supports the following keys:

  • Driver - Specifies the task driver that should be used to run the task. See the driver documentation for what is available. Examples include docker, qemu, java, and exec.

  • Constraints - This is a list of Constraint objects. See the constraint reference for more details.

  • Config - A map of key/value configuration passed into the driver to start the task. The details of configurations are specific to each driver.

  • Services - Nomad integrates with Consul for service discovery. A service block represents a routable and discoverable service on the network. Nomad automatically registers when a task is started and de-registers it when the task transitions to the dead state. Click here to learn more about services.

  • Env - A map of key/value representing environment variables that will be passed along to the running process. Nomad variables are interpreted when set in the environment variable values. See the table of interpreted variables here.

    For example the below environment map will be reinterpreted:

        "Env": {
        "NODE_CLASS" : "${nomad.class}"
    }

  • Resources - Provides the resource requirements of the task. See the resources reference for more details.

  • Meta - Annotates the task group with opaque metadata.

  • KillTimeout - KillTimeout is a time duration in nanoseconds. It can be used to configure the time between signaling a task it will be killed and actually killing it. Drivers first sends a task the SIGINT signal and then sends SIGTERM if the task doesn't die after the KillTimeout duration has elapsed.

  • LogConfig - This allows configuring log rotation for the stdout and stderr buffers of a Task. See the log rotation reference below for more details.

Resources

The Resources object supports the following keys:

  • CPU - The CPU required in MHz.

  • DiskMB - The disk required in MB.

  • IOPS - The number of IOPS required given as a weight between 10-1000.

  • MemoryMB - The memory required in MB.

  • Networks - A list of network objects.

The Network object supports the following keys:

  • MBits - The number of MBits in bandwidth required.

Nomad can allocate two types of ports to a task - Dynamic and Static ports. A network object allows the user to specify a list of DynamicPorts orj StaticPorts. Each object supports the following attributes:

  • Value - The port number for static ports. If the port is dynamic, then this attribute is ignored.
  • Label - The label to annotate a port so that it can be referred in the service discovery block or environment variables.

Restart Policy

The RestartPolicy object supports the following keys:

  • Attempts - attempts is the number of restarts allowed in an interval.

  • Interval - interval is a time duration that can be specified using the s, m, and h suffixes, such as 30s. The interval begins when the first task starts and ensures that only attempts number of restarts happens within it. If more than attempts number of failures happen, behavior is controlled by mode.

  • Delay - A duration to wait before restarting a task. It is specified in nanoseconds. A random jitter of up to 25% is added to the delay.

  • Mode - Controls the behavior when the task fails more than Attempts times in an interval. Possible values are listed below:

    • delay - delay will delay the next restart until the next Interval is reached.

    • fail - fail will not restart the task again.

Constraint

The Constraint object supports the following keys:

  • Attribute - Specifies the attribute to examine for the constraint. See the table of attributes here.

  • Operator - Specifies the comparison operator. Defaults to equality, and can be =, ==, is, !=, not, >, >=, <, <=. The ordering is compared lexically.

  • Value - Specifies the value to compare the attribute against. This can be a literal value or another attribute.

  • Version - Specifies a version constraint against the attribute. This sets the operator to version and the value to what is specified. This supports a comma separated list of constraints, including the pessimistic operator. See the go-version repository for examples.

  • Regexp - Specifies a regular expression constraint against the attribute. This sets the operator to "regexp" and the value to the regular expression.

  • DistinctHosts - DistinctHosts accepts a boolean true. The default is false.

    When DistinctHosts is true at the Job level, each instance of all task Groups specified in the job is placed on a separate host.

    When DistinctHosts is true at the task group level with count > 1, each instance of a task group is placed on a separate host. Different task groups in the same job may be co-scheduled.

    Tasks within a task group are always co-scheduled.

Log Rotation

The LogConfig object configures the log rotation policy for a task's stdout and stderr. The LogConfig object supports the following attributes:

  • MaxFiles - The maximum number of rotated files Nomad will retain for stdout and stderr, each tracked individually.

  • MaxFileSize - The size of each rotated file. The size is specified in MB.

If the amount of disk resource requested for the task is less than the total amount of disk space needed to retain the rotated set of files, Nomad will return a validation error when a job is submitted.

"LogConfig: {
    "MaxFiles": 3,
    "MaxFileSizeMB": 10
}

In the above example we have asked Nomad to retain 3 rotated files for both stderr and stdout and size of each file is 10MB. The minimum disk space that would be required for the task would be 60MB.

Artifact

Nomad downloads artifacts using go-getter. The go-getter library allows downloading of artifacts from various sources using a URL as the input source. The key/value pairs given in the options block map directly to parameters appended to the supplied source url. These are then used by go-getter to appropriately download the artifact. go-getter also has a CLI tool to validate its URL and can be used to check if the Nomad artifact is valid.

Nomad allows downloading http, https, and S3 artifacts. If these artifacts are archives (zip, tar.gz, bz2, etc.), these will be unarchived before the task is started.

The Artifact object maps supports the following keys:

  • GetterSource - The path to the artifact to download.

  • RelativeDest - The destination to download the artifact relative the task's directory.

  • GetterOptions - A map[string]string block of options for go-getter. An example is given below:

"GetterOptions": {
    "checksum": "md5:c4aa853ad2215426eb7d70a21922e794",

    "aws_access_key_id": "<id>",
    "aws_access_key_secret": "<secret>",
    "aws_access_token": "<token>"
}