Expressions

Expressions is a powerful tool that allows formulating complex filters for playbook events. Playbook event filters use Common Expression Language (CEL).

The Common Expression Language (CEL) is a non-Turing complete language designed for simplicity, speed, safety, and portability. CEL's C-like syntax looks nearly identical to equivalent expressions in C++, Go, Java, and TypeScript.

Examples:

notify-with-filter.yaml
---
apiVersion: mission-control.flanksource.com/v1
kind: Playbook
metadata:
  name: notify-with-filter
spec:
  on:
    config:
      - event: created
  configs:
    - type: Kubernetes::Pod
  actions:
    - name: Send notification
      exec:
        script: notify-send "{{.config.name}} was created"
    - name: Bad script to create a failing action
      exec:
        script: non-existing-command
    - name: Send all success notification
      if: success() # this filter practically skips this action as the second action above always fails
      exec:
        script: notify-send "Everything went successfully"
    - name: Send notification regardless
      if: always()
      exec:
        script: notify-send "a config was created"

Conditionally running actions

Playbook actions can be selectively executed based on CEL expressions. These expressions must either return

• a boolean value (true indicating run the action & skip the action otherwise)
• or a special function among the ones listed below

Function	Description
always()	run no matter what; even if the playbook is cancelled/fails
failure()	run if any of the previous actions failed
skip()	skip running this action
success()	run only if all previous actions succeeded (default)
timeout()	run only if any of the previous actions timed out

Examples

• if: config.deleted_at ? true: false
• if: always()

Context

Expressions have access to the following variables and functions

Field	Description	Schema
.config	Config passed to the playbook	ConfigItem
.component	Component passed to the playbook	Component
.check	Canary Check passed to the playbook	Check
.params	User provided parameters to the playbook	map[string]string
.user.name	Name of the user who invoked the action	string
.user.email	Email of the user who invoked the action	string