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Workflows

Workflows allow us to chain actions together, implement conditional logic and branching, and turn actions into composable automations.

Workflows are actions too! They simply use a different runner_type: mistral-v2.

We'll demonstrate workflows by creating one that retrieves the NASA APOD picture URL then publish this URL to a RabbitMQ Queue.

Create workflow action metadata

The workflow action's metadata file is just like any other action metadata file. It has runner_type: mistral-v2, input parameters just like the a Python action, and entry_point set to the path of workflow definition YAML file (relative to the pack's actions/ directory)

Edit /opt/stackstorm/packs/tutorial/actions/nasa_apod_rabbitmq_publish.yaml and insert the following content:

---
name: nasa_apod_rabbitmq_publish
pack: tutorial
description: "Queries NASA's APOD (Astronomy Picture Of the Day) API to get the link to the picture of the day, then publishes that link to a RabbitMQ queue"
runner_type: "mistral-v2"
enabled: true
entry_point: workflows/nasa_apod_rabbitmq_publish.yaml
parameters:
  date:
    type: string
    description: "The date [YYYY-MM-DD] of the APOD image to retrieve."
  message:
    type: string
    description: "Extra message to publish with the URL"
  host:
    type: string
    default: "127.0.0.1"
  exchange:
    type: string
    default: "demo"
    description: "Name of the RabbitMQ exchange"
  exchange_type:
    type: string
    default: "topic"
    description: "Type of the RabbitMQ exchange"
  routing_key:
    type: string
    default: "demokey"
    description: "Name of the RabbitMQ routing key"

NOTE If you're struggling and just need the answer, simply copy the file from our answers directory:

cp /opt/stackstorm/packs/tutorial/etc/answers/actions/nasa_apod_rabbitmq_publish.yaml /opt/stackstorm/packs/tutorial/actions/nasa_apod_rabbitmq_publish.yaml

We need to tell StackStorm about our new action metadata file:

st2ctl reload --register-actions

Create the workflow

StackStorm has several different Workflow engines including ActionChain, Mistral, and the upcoming Orchestra. We're going to be using Mistral for this example.

In our workflow we want to call tutorial.nasa_apod to retrieve our image URL. Next we'll publish this as a message to RabbitMQ using the twitter.update_status action.

Note The name of the workflow within the workflow file, MUST be the same as the name of the StackStorm pack.action:

Edit /opt/stackstorm/packs/tutorial/actions/workflows/nasa_apod_rabbitmq_publish.yaml

Content:

version: '2.0'

tutorial.nasa_apod_rabbitmq_publish:
  type: direct
  input:
    - date
    - message
    - host
    - exchange
    - exchange_type
    - routing_key

  tasks:
    get_apod_url:
      action: tutorial.nasa_apod
      input:
        date: "{{ _.date }}"
      publish:
        apod_url: "{{ task('get_apod_url').result.result.url }}"
      on-success:
        - publish_to_rabbitmq

    publish_to_rabbitmq:
      action: rabbitmq.publish_message
      input:
        host: "{{ _.host }}"
        exchange: "{{ _.exchange }}"
        exchange_type: "{{ _.exchange_type }}"
        routing_key: "{{ _.routing_key }}"
        message: "{{ _.apod_url }}{%if _.message %} {{ _.message }}{% endif %}"

NOTE If you're struggling and just need the answer, simply copy the file from our answers directory:

cp /opt/stackstorm/packs/tutorial/etc/answers/actions/workflows/nasa_apod_rabbitmq_publish.yaml /opt/stackstorm/packs/tutorial/actions/workflows/nasa_apod_rabbitmq_publish.yaml

Test

Run our action, creating a new message!

st2 run tutorial.nasa_apod_rabbitmq_publish date="2018-07-04"

Read from the queue to see if our message was delivered:

rabbitmqadmin get queue=demoqueue count=99