Conditional step execution

You can use the when key to control whether or not Relay executes a step.

If the when key is present in a step definition, Relay determines whether the step should execute by evaluating its content. The when key is a single boolean expression or an array of boolean expressions that are combined using the && operator. If the key evalutes to true, Relay executes the step. Otherwise, the step is skipped.

Note that there is no type coercion applied to when values. If the content cannot be evaluated to a boolean, the step will produce an error and your workflow run will fail.

steps:
- name: example
  image: alpine
  when: ${parameters.env == 'development'}

In this example, Relay only executes the example step if the env parameter is development.

Writing conditions

Relay's template engine includes a comprehensive set of boolean and comparison operators that can be used to produce values for when keys.

Example of a workflow with conditional execution

Consider a scenario where you have two environments, development and production. You want to deploy a monitoring system only against production. In the following workflow, the deploy-monitoring step uses when along with the != operator to make sure that Relay only deploys the monitoring system when env is not development.

Similarly, in this scenario, you want to send a notification to Slack when you deploy to production. The slack-notify step uses when together with the == operator to ensure that Relay only notifies Slack when env is production.

description: Deploy a thing to environments then conditionally notify slack

parameters:
  channel:
    description: Slack channel (include preceding hashtag)
  env:
    description: the environment to deploy to
    default: development

steps:
- name: deploy-monitoring
  image: alpine:latest
  input:
  - echo "Deploying monitoring to system"
  when: ${parameters.env != 'development'}

- name: slack-notify
  image: relaysh/slack-step-message-send
  spec:
    apitoken: ${secrets.'slack-token'}
    channel: ${parameters.channel}
    message: "production was deployed"
  dependsOn:
  - deploy-monitoring
  when: ${parameters.env == 'production'}