Job Specs

Overview

Job specs are saved in the job specs directory (e.g. specs/{spec-id}/spec.yml). At runtime, Jobson uses the job spec to figure out a job’s:

  • name: and description:
  • expectedInputs: from clients
  • execution: of the application:, once the inputs are provided
  • execution: arguments:, which may include some of the inputs
  • execution: dependencies:, such as scripts or data files that should be copied into the runtime working directory
  • expectedOutputs: from the application, which Jobson should persist

A basic example of a job spec would be:

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---

name: Demo Job Spec

description: >

  A demo job spec generated when creating a new Jobson deployment. Try it out!

expectedInputs:

- id: firstName
  type: string
  name: First Name
  description: Your first name
  default: Jeff

execution:

  dependencies:
  - source: demo-script.sh
    target: demo-script.sh

  application: bash
  arguments:
  - demo-script.sh
  - ${inputs.firstName}

expectedOutputs:

- id: output-from-script.jpg
  path: output
  name: Output from Script
  description: An output generated by the runtime script
  mimeType: image/jpeg
  metadata:
    embed: true

This example specifies:

  • A job with a human-readable name: of Demo   Job Spec (and description:).
  • That expects clients to provide a single string input called firstName, which defaults to Jeff if clients don’t provide it
  • That, once it receives the inputs:
  • Copies demo-script.sh from the job spec’s directory to demo-script.sh in the job’s working directory
  • Executes bash with demo-script.sh and ${inputs.firstName} with two
  • arguments: - demo-script.sh: The script bash should run -
  • ${inputs.firstName}: The firstName provided as an input -
  • Before executing, Jobson should copy demo-script.sh from the job
  • spec folder to the job’s working directory -

This specifies a job that takes a single string input (firstName) and runs a bash script (demo-script.sh). The bash script is copied from the spec directory (dependencies: source: demo-script.sh) into the job’s working directory (dependencies: target: demo-script.sh). Once the script runs, it produces a file called output, which has an image/jpeg MIME type and should be persisted as ${request.id}.jpg by Jobson.

Creating a Job Spec

The Jobson command-line interface comes with a basic spec generator for creating a bareboes spec:

$ jobson generate spec new-spec

This creates a job spec with an ID of new-spec at jobs/new-spec/spec.yml.

spec.yml Schema

Job specs are standard YAML files that should appear at the correct path (e.g. jobs/{job-id}/spec.yml). This section describes what can be put into the spec.yml files.

name

Name of the Job Spec.

description

Detailed Description of the Job Spec

expectedInputs

What Input Data Should be Provided to Execute a Job

execution

What Executes Once the Input Data is Received.

expectedOutputs

What is Produced by Execution (and should be persisted by Jobson).

TODO: Work in progress. Need documentation about supported data types, scripting functions, etc.

Template Strings

Template strings, such as ${request.id} allow developers to add runtime evaluation to their job specs. For example, template strings allow runtime input arguments to be used as application arguments:

execution:
  application: bash
  arguments:
  - ${inputs.firstName}

This is the main way of passing client inputs into an application at runtime.

Template strings are ordinary strings with support for special expressions between ${ and }. Jobson interprets those expressions at runtime, evaluating them against an environment containing data (e.g. inputs, request) and functions (e.g. toJSON, toFile).

Template strings have access to the following:

String toJSON(Object arg)

A function that takes an input (e.g. request, request.id, 'string literal') and returns a JSON representation of the input. Object-/Hash-like arguments are converted into a JSON object, strings are converted into a JSON string, numbers into JSON numbers, etc.

String toFile(String content)

A function that takes a string input (e.g. request.id, toJSON(request)), write the input to a file, and returns an absolute path to that file.

String join(String delimiter, StringArray strings)

A function that takes a delimiter (e.g. ',') and a StringArray (usually, from a Jobson string[] expectedInput) and returns a string that contains each element in the StringArray joined with the delimiter.

String toString(Object arg)

A function that takes an argument (e.g. request.firstName) and returns a string representation of that arugment. Note: internally, this uses the Java .toString method on the argument, which may produce non-obvious results with complex arguments.

Object request

A reference to the request that initiated the job. Useful fields in the request are:

  • String id: The job’s ID (e.g. 57s9fmopb)
  • String owner: The client that initaited the job request (e.g. foouser)
  • String name: The name the client given the job
  • Map<JobExpectedInputId, JobInput> inputs: The inputs given for the job.
  • Each input is accessible via the dot accessor (e.g. request.inputs.firstName).
  • The Map is serializable as JSON (e.g. toJSON(request.inputs)).
  • JobSpec spec: The job spec the job was submitted against

Object inputs

Shortcut for request.inputs.

String outputDir

The output directory for the job. At time of writing, this is always the same as the job’s working directory.