Sub-DAG Composition

The call: step type executes another DAG as a sub-step within the current run.

Basic usage

name: full-pipeline
steps:
  - id: etl
    call:
      dag: daily-etl
      params:
        dept: "{{ .Params.department }}"
  - id: report
    script: reports/summary.R
    depends: [etl]

The daily-etl DAG runs to completion (or failure) as part of full-pipeline. If it fails, the etl step fails and downstream steps are blocked.

Parameter passing

Pass parameters from the parent DAG to the sub-DAG:

call:
  dag: model-pipeline
  params:
    dataset: "{{ .Params.dataset }}"
    algo: lm

These override the sub-DAG’s parameter defaults.

Output propagation

Outputs from the sub-DAG’s steps are available in the parent DAG via the standard DAGGLE_OUTPUT_* environment variables, namespaced by the calling step ID.

When to use call: vs on_dag triggers

	call: step	on_dag: trigger
Relationship	Parent controls child	Independent DAGs
Execution	Inline, blocks parent	Async, separate run
Failure	Fails the parent step	Does not affect upstream DAG
Scheduling	Part of parent’s run	Triggered by events
Use case	Modular pipeline composition	Loose coupling between workflows

Use call: when the sub-DAG is a logical part of the parent workflow. Use on_dag: triggers when DAGs are independent but sequenced.