Parallel Execution

Parallel Execution

Run multiple steps concurrently using parallel: blocks. Steps inside a parallel block execute simultaneously, and their outputs merge back for subsequent sequential steps.

Syntax

steps:
  - name: build_all
    parallel:
      - name: build_frontend
        func: shell
        do: |
          echo "Building frontend..."
          echo "FRONTEND_RESULT=success"
        outputs:
          result: '{{ result.output | regexFind "FRONTEND_RESULT=(.+)" }}'

      - name: build_backend
        func: shell
        do: |
          echo "Building backend..."
          echo "BACKEND_RESULT=success"
        outputs:
          result: '{{ result.output | regexFind "BACKEND_RESULT=(.+)" }}'

  - name: deploy
    func: shell
    do: |
      echo "Frontend: {{ steps.build_frontend.result }}"
      echo "Backend: {{ steps.build_backend.result }}"

How It Works

1. Steps inside parallel: launch concurrently (one goroutine per step)
2. Each parallel step gets an isolated copy of the variable context
3. The parallel block waits for all children to complete
4. Outputs from all children merge into the main context
5. Sequential steps after the block can reference any parallel step’s outputs

Error Handling

If any parallel step fails, the entire block fails. All steps run to completion — failures are collected and reported after all finish.

Constraints

• Parallel steps should be independent — they cannot reference each other’s outputs
• Each step gets a snapshot of variables from before the block — mutations don’t cross between parallel steps
• Nested parallel blocks are supported but use with caution
• Step names must be unique across the entire task (including inside parallel blocks)

Use Cases

• Build multiple artifacts simultaneously
• Run health checks on multiple services at once
• Execute independent validation steps in parallel
• Fan-out operations across multiple targets