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api JSON Job Specification - HTTP API api-jobs Jobs can also be specified via the HTTP API using a JSON format. This guide discusses the job specification in JSON format.

JSON Job Specification

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 my-job.nomad

Syntax

Below is the JSON representation of the job outputed by $ nomad init:

{
    "Job": {
        "ID": "example",
        "Name": "example",
        "Type": "service",
        "Priority": 50,
        "Datacenters": [
            "dc1"
        ],
        "TaskGroups": [{
            "Name": "cache",
            "Count": 1,
            "Tasks": [{
                "Name": "redis",
                "Driver": "docker",
                "User": "",
                "Config": {
                    "image": "redis:3.2",
                    "port_map": [{
                        "db": 6379
                    }]
                },
                "Services": [{
                    "Id": "",
                    "Name": "global-redis-check",
                    "Tags": [
                        "global",
                        "cache"
                    ],
                    "PortLabel": "db",
                    "AddressMode": "",
                    "Checks": [{
                        "Id": "",
                        "Name": "alive",
                        "Type": "tcp",
                        "Command": "",
                        "Args": null,
                        "Path": "",
                        "Protocol": "",
                        "PortLabel": "",
                        "Interval": 10000000000,
                        "Timeout": 2000000000,
                        "InitialStatus": "",
                        "TLSSkipVerify": false
                    }]
                }],
                "Resources": {
                    "CPU": 500,
                    "MemoryMB": 256,
                    "Networks": [{
                        "Device": "",
                        "CIDR": "",
                        "IP": "",
                        "MBits": 10,
                        "DynamicPorts": [{
                            "Label": "db",
                            "Value": 0
                        }]
                    }]
                },
                "Leader": false
            }],
            "RestartPolicy": {
                "Interval": 300000000000,
                "Attempts": 10,
                "Delay": 25000000000,
                "Mode": "delay"
            },
            "EphemeralDisk": {
                "SizeMB": 300
            }
        }],
        "Update": {
            "MaxParallel": 1,
            "MinHealthyTime": 10000000000,
            "HealthyDeadline": 180000000000,
            "AutoRevert": false,
            "Canary": 0
        }
    }
}

The example JSON could be submitted as a job using the following:

$ curl -XPUT @d example.json http://127.0.0.1:4646/v1/job/example
{
  "EvalID": "5d6ded54-0b2a-8858-6583-be5f476dec9d",
  "EvalCreateIndex": 12,
  "JobModifyIndex": 11,
  "Warnings": "",
  "Index": 12,
  "LastContact": 0,
  "KnownLeader": false
}

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.

  • ParameterizedJob - Specifies the job as a parameterized job such that it can be dispatched against. The ParamaterizedJob object supports the following attributes:

    • MetaOptional - Specifies the set of metadata keys that may be provided when dispatching against the job as a string array.

    • MetaRequired - Specifies the set of metadata keys that must be provided when dispatching against the job as a string array.

    • Payload - Specifies the requirement of providing a payload when dispatching against the parameterized job. The options for this field are "optional", "required" and "forbidden". The default value is "optional".

  • Payload - The payload may not be set when submitting a job but may appear in a dispatched job. The Payload will be a base64 encoded string containing the payload that the job was dispatched with. The payload has a maximum size of 16 KiB.

  • 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 an update strategy to be applied to all task groups within the job. When specified both at the job level and the task group level, the update blocks are merged with the task group's taking precedence. For more details on the update stanza, please see below.

  • Periodic - Periodic allows the job to be scheduled at fixed times, dates or intervals. The periodic expression is always evaluated in the UTC timezone to ensure consistent evaluation when Nomad Servers span multiple time zones. The Periodic object is optional and supports the following attributes:

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

    • time_zone - Specifies the time zone to evaluate the next launch interval against. This is useful when wanting to account for day light savings in various time zones. The time zone must be parsable by Golang's LoadLocation. The default is UTC.

    • 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 TaskGroup objects, each supports the following attributes:

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

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

  • Meta - A key-value map that annotates the task group with opaque metadata.

  • Name - The name of the task group. Must be specified.

  • 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.

  • EphemeralDisk - Specifies the group's ephemeral disk requirements. See the ephemeral disk reference for more details.

  • Update - Specifies an update strategy to be applied to all task groups within the job. When specified both at the job level and the task group level, the update blocks are merged with the task group's taking precedence. For more details on the update stanza, please see below.

  • Tasks - A list of Task object that are part of the task group.

Task

The Task object supports the following keys:

  • Artifacts - Artifacts is a list of Artifact objects which define artifacts to be downloaded before the task is run. See the artifacts 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.

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

  • DispatchPayload - Configures the task to have access to dispatch payloads. The DispatchPayload object supports the following attributes:

    • File - Specifies the file name to write the content of dispatch payload to. The file is written relative to the task's local directory.

  • 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.

  • 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}"
  }
}

  • 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. The default KillTimeout is 5 seconds.

  • leader - Specifies whether the task is the leader task of the task group. If set to true, when the leader task completes, all other tasks within the task group will be gracefully shutdown.

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

  • Meta - Annotates the task group with opaque metadata.

  • Name - The name of the task. This field is required.

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

  • Services - Services is a list of Service objects. Nomad integrates with Consul for service discovery. A Service object 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. Below is the fields in the Service object:

    • Name: An explicit name for the Service. Nomad will replace ${JOB}, ${TASKGROUP} and ${TASK} by the name of the job, task group or task, respectively. ${BASE} expands to the equivalent of ${JOB}-${TASKGROUP}-${TASK}, and is the default name for a Service. Each service defined for a given task must have a distinct name, so if a task has multiple services only one of them can use the default name and the others must be explicitly named. Names must adhere to RFC-1123 §2.1 and are limited to alphanumeric and hyphen characters (i.e. [a-z0-9\-]), and be less than 64 characters in length.

    • Tags: A list of string tags associated with this Service. String interpolation is supported in tags.

    • PortLabel: PortLabel is an optional string and is used to associate a port with the service. If specified, the port label must match one defined in the resources block. This could be a label of either a dynamic or a static port.

    • Checks: Checks is an array of check objects. A check object defines a health check associated with the service. Nomad supports the script, http and tcp Consul Checks. Script checks are not supported for the qemu driver since the Nomad client doesn't have access to the file system of a task using the Qemu driver.

      • Type: This indicates the check types supported by Nomad. Valid options are currently script, http and tcp.

      • Name: The name of the health check.

      • Interval: This indicates the frequency of the health checks that Consul will perform.

      • Timeout: This indicates how long Consul will wait for a health check query to succeed.

      • Path: The path of the HTTP endpoint which Consul will query to query the health of a service if the type of the check is http. Nomad will add the IP of the service and the port, users are only required to add the relative URL of the health check endpoint.

      • Protocol: This indicates the protocol for the HTTP checks. Valid options are http and https. We default it to http.

      • Command: This is the command that the Nomad client runs for doing script based health check.

      • Args: Additional arguments to the command for script based health checks.

    • TLSSkipVerify: If true, Consul will not attempt to verify the certificate when performing HTTPS checks. Requires Consul >= 0.7.2.

  • Templates - Specifies the set of Template objects to render for the task. Templates can be used to inject both static and dynamic configuration with data populated from environment variables, Consul and Vault.

  • User - Set the user that will run the task. It defaults to the same user the Nomad client is being run as. This can only be set on Linux platforms.

Resources

The Resources object supports the following keys:

  • CPU - The CPU required in MHz.

  • 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/Reserved ports. A network object allows the user to specify a list of DynamicPorts and ReservedPorts. 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.

Ephemeral Disk

The EphemeralDisk object supports the following keys:

  • Migrate - Specifies that the Nomad client should make a best-effort attempt to migrate the data from a remote machine if placement cannot be made on the original node. During data migration, the task will block starting until the data migration has completed. Value is a boolean and the default is false.

  • SizeMB - Specifies the size of the ephemeral disk in MB. Default is 300.

  • Sticky - Specifies that Nomad should make a best-effort attempt to place the updated allocation on the same machine. This will move the local/ and alloc/data directories to the new allocation. Value is a boolean and the default is false.

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 is specified in nanoseconds. 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 - Mode is given as a string and 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.

Update

Specifies the task group update strategy. When omitted, rolling updates are disabled. The update stanza can be specified at the job or task group level. When specified at the job, the update stanza is inherited by all task groups. When specified in both the job and in a task group, the stanzas are merged with the task group's taking precedence. 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.

  • HealthCheck - Specifies the mechanism in which allocations health is determined. The potential values are:

    • "checks" - Specifies that the allocation should be considered healthy when all of its tasks are running and their associated [checks][] are healthy, and unhealthy if any of the tasks fail or not all checks become healthy. This is a superset of "task_states" mode.

    • "task_states" - Specifies that the allocation should be considered healthy when all its tasks are running and unhealthy if tasks fail.

    • "manual" - Specifies that Nomad should not automatically determine health and that the operator will specify allocation health using the HTTP API.

  • MinHealthyTime - Specifies the minimum time the allocation must be in the healthy state before it is marked as healthy and unblocks further allocations from being updated. This is specified using a label suffix like "30s" or "15m".

  • HealthyDeadline - Specifies the deadline in which the allocation must be marked as healthy after which the allocation is automatically transitioned to unhealthy. This is specified using a label suffix like "2m" or "1h".

  • AutoRevert - Specifies if the job should auto-revert to the last stable job on deployment failure. A job is marked as stable if all the allocations as part of its deployment were marked healthy.

  • Canary - Specifies that changes to the job that would result in destructive updates should create the specified number of canaries without stopping any previous allocations. Once the operator determines the canaries are healthy, they can be promoted which unblocks a rolling update of the remaining allocations at a rate of max_parallel.

  • Stagger - Specifies the delay between migrating allocations off nodes marked for draining. This is specified using a label suffix like "30s" or "1h".

An example Update block:

{
  "Update": {
        "MaxParallel": 3,
        "HealthCheck": "checks",
        "MinHealthyTime": 15000000000,
        "HealthyDeadline": 180000000000,
        "AutoRevert": false,
        "Canary": 1
  }
}

Constraint

The Constraint object supports the following keys:

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

  • RTarget - Specifies the value to compare the attribute against. This can be a literal value, another attribute or a regular expression if the Operator is in "regexp" mode.

  • Operand - Specifies the test to be performed on the two targets. It takes on the following values:

    • regexp - Allows the RTarget to be a regular expression to be matched.

    • set_contains - Allows the RTarget to be a comma separated list of values that should be contained in the LTarget's value.

    • distinct_host - If set, the scheduler will not co-locate any task groups on the same machine. This can be specified as a job constraint which applies the constraint to all task groups in the job, or as a task group constraint which scopes the effect to just that group. The constraint may not be specified at the task level.

      Placing the constraint at both the job level and at the task group level is
redundant since when placed at the job level, the constraint will be applied
to all task groups. When specified, `LTarget` and `RTarget` should be
omitted.

    • distinct_property - If set, the scheduler selects nodes that have a distinct value of the specified property. The RTarget specifies how many allocations are allowed to share the value of a property. The RTarget must be 1 or greater and if omitted, defaults to 1. This can be specified as a job constraint which applies the constraint to all task groups in the job, or as a task group constraint which scopes the effect to just that group. The constraint may not be specified at the task level.

      Placing the constraint at both the job level and at the task group level is
redundant since when placed at the job level, the constraint will be applied
to all task groups. When specified, `LTarget` should be the property
that should be distinct and and `RTarget` should be omitted.

    • Comparison Operators - =, ==, is, !=, not, >, >=, <, <=. The ordering is compared lexically.

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.

  • MaxFileSizeMB - 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 10 MB. The minimum disk space that would be required for the task would be 60 MB.

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 supports the following keys:

  • GetterSource - The path to the artifact to download.

  • RelativeDest - An optional path to download the artifact into relative to the root of the task's directory. If omitted, it will default to local/.

  • GetterOptions - A map[string]string block of options for go-getter. Full documentation of supported options are available here. An example is given below:

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

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

An example of downloading and unzipping an archive is as simple as:

{
  "Artifacts": [
    {
      "GetterSource": "https://example.com/my.zip",
      "GetterOptions": {
        "checksum": "md5:7f4b3e3b4dd5150d4e5aaaa5efada4c3"
      }
    }
  ]
}

S3 examples

S3 has several different types of addressing and more detail can be found here

S3 region specific endpoints can be found here

Path based style:

{
  "Artifacts": [
    {
      "GetterSource": "https://s3-us-west-2.amazonaws.com/my-bucket-example/my_app.tar.gz",
    }
  ]
}

or to override automatic detection in the URL, use the S3-specific syntax

{
  "Artifacts": [
    {
      "GetterSource": "s3::https://s3-eu-west-1.amazonaws.com/my-bucket-example/my_app.tar.gz",
    }
  ]
}

Virtual hosted based style

{
  "Artifacts": [
    {
      "GetterSource": "my-bucket-example.s3-eu-west-1.amazonaws.com/my_app.tar.gz",
    }
  ]
}

Template

The Template block instantiates an instance of a template renderer. This creates a convenient way to ship configuration files that are populated from environment variables, Consul data, Vault secrets, or just general configurations within a Nomad task.

Nomad utilizes a tool called Consul Template. Since Nomad v0.5.3, the template can reference Nomad's runtime environment variables. For a full list of the API template functions, please refer to the Consul Template README.

Template object supports following attributes:

  • ChangeMode - Specifies the behavior Nomad should take if the rendered template changes. The default value is "restart". The possible values are:

    • "noop" - take no action (continue running the task)
    • "restart" - restart the task
    • "signal" - send a configurable signal to the task

  • ChangeSignal - Specifies the signal to send to the task as a string like "SIGUSR1" or "SIGINT". This option is required if the ChangeMode is signal.

  • DestPath - Specifies the location where the resulting template should be rendered, relative to the task directory.

  • EmbeddedTmpl - Specifies the raw template to execute. One of SourcePath or EmbeddedTmpl must be specified, but not both. This is useful for smaller templates, but we recommend using SourcePath for larger templates.

  • Envvars - Specifies the template should be read back as environment variables for the task.

  • LeftDelim - Specifies the left delimiter to use in the template. The default is "{{" for some templates, it may be easier to use a different delimiter that does not conflict with the output file itself.

  • Perms - Specifies the rendered template's permissions. File permissions are given as octal of the Unix file permissions rwxrwxrwx.

  • RightDelim - Specifies the right delimiter to use in the template. The default is "}}" for some templates, it may be easier to use a different delimiter that does not conflict with the output file itself.

  • SourcePath - Specifies the path to the template to be rendered. SourcePath is mutually exclusive with EmbeddedTmpl attribute. The source can be fetched using an Artifact resource. The template must exist on the machine prior to starting the task; it is not possible to reference a template inside of a Docker container, for example.

  • Splay - Specifies a random amount of time to wait between 0 ms and the given splay value before invoking the change mode. Should be specified in nanoseconds.

{
  "Templates": [
    {
      "SourcePath": "local/config.conf.tpl",
      "DestPath": "local/config.conf",
      "EmbeddedTmpl": "",
      "ChangeMode": "signal",
      "ChangeSignal": "SIGUSR1",
      "Splay": 5000000000
    }
  ]
}