Core Concepts

Essential concepts for working with Dagu.

DAG (Directed Acyclic Graph)

A DAG defines your workflow as a graph of dependencies:

• Directed: Steps execute in a specific order
• Acyclic: No circular dependencies allowed
• Graph: Steps connected by dependency relationships

Workflow Components

Steps

The basic unit of execution. Each step runs a command:

steps:
  - curl -O https://example.com/data.csv  # Download data
  - python analyze.py data.csv           # Process data

Dependencies

By default, steps run sequentially. Use depends for parallel execution:

steps:
  - name: A
    command: echo "First"
    
  - name: B
    command: echo "Second (after A)"
    
  - name: C
    command: echo "Parallel with B"
    depends: A  # Only depends on A, runs parallel to B
    
  - name: D
    command: echo "After both B and C"
    depends: [B, C]

Parameters

params:
  - ENV: dev
  - REGION: us-east-1

steps:
  - echo "Deploying to ${ENV} in ${REGION}"

Override at runtime:

dagu start workflow.yaml -- ENV=prod REGION=eu-west-1

Variables

Pass data between steps using output:

steps:
  - command: date +%Y%m%d
    output: TODAY
  - tar -czf backup_${TODAY}.tar.gz /data

Status Management

Execution States

• queued: DAG is waiting to be executed
• running: DAG is currently executing
• success: All steps completed successfully
• partial_success: Some steps failed but execution continued (via continueOn)
• failed: DAG execution failed
• cancelled: DAG was manually cancelled

Status Transitions

Step Status

• pending: Step is waiting for dependencies
• running: Step is executing
• success: Step completed successfully
• failed: Step execution failed
• cancelled: Step was cancelled
• skipped: Step was skipped (precondition not met)

Status Hooks

handlerOn:
  success:
    command: notify-team.sh "Workflow completed"
  failure:
    command: alert-oncall.sh "Workflow failed"
  partial_success:
    command: log-partial.sh "Some steps failed"

Executors

Shell (Default)

Runs commands in the system shell:

steps:
  - command: echo "Hello"
    shell: bash  # or sh, zsh

See Shell Executor for more details.

Docker

Execute in containers:

container:
  image: python:3.11
  workingDir: /app
  volumes:
    - /app/data:/data
steps:
  - python script.py

See Docker Executor for more details.

SSH

Run on remote machines:

ssh:
  user: ubuntu
  host: server.example.com
  key: ~/.ssh/id_rsa

steps:
  - echo "Running remote script"

See SSH Executor for more details.

HTTP

Make API calls:

steps:
  - executor:
      type: http
      config:
        method: POST
        url: https://api.example.com/trigger
        headers:
          Authorization: Bearer ${API_TOKEN}

See HTTP Executor for more details.

Scheduling

Cron-based scheduling:

schedule: "0 2 * * *"  # Daily at 2 AM

Multiple schedules:

schedule:
  - "0 9 * * MON-FRI"  # Weekdays at 9 AM
  - "0 14 * * SAT,SUN" # Weekends at 2 PM

Start/stop schedules:

schedule:
  start: "0 8 * * *"   # Start at 8 AM
  stop: "0 18 * * *"   # Stop at 6 PM

See Scheduling for more details.

Lifecycle Handlers

Execute commands on workflow events:

handlerOn:
  success:
    command: echo "Workflow succeeded"
    
  failure:
    command: |
      echo "Workflow failed" | mail -s "Alert" [email protected]
      
  cancel:
    command: echo "Cleaning up resources"
    
  exit:
    command: echo "Always runs"

See Also

• Writing Workflows - Create your own workflows
• Examples - Ready-to-use patterns
• CLI Reference - Command-line usage