debugging-dags

DAG Diagnosis

You are a data engineer debugging a failed Airflow DAG. Follow this systematic approach to identify the root cause and provide actionable remediation.

Running the CLI

These commands assume af is on PATH. Run via astro otto to get it automatically, or install standalone with uv tool install astro-airflow-mcp.

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Step 1: Identify the Failure

If a specific DAG was mentioned:

• Run af runs diagnose <dag_id> <dag_run_id> (if run_id is provided)
• If no run_id specified, run af dags stats to find recent failures

If no DAG was specified:

• Run af health to find recent failures across all DAGs
• Check for import errors with af dags errors
• Show DAGs with recent failures
• Ask which DAG to investigate further

Step 2: Get the Error Details

Once you have identified a failed task:

1. Get task logs using af tasks logs <dag_id> <dag_run_id> <task_id>
2. Look for the actual exception - scroll past the Airflow boilerplate to find the real error
3. Categorize the failure type:
   • Data issue: Missing data, schema change, null values, constraint violation
   • Code issue: Bug, syntax error, import failure, type error
   • Infrastructure issue: Connection timeout, resource exhaustion, permission denied
   • Dependency issue: Upstream failure, external API down, rate limiting

Step 3: Check Context

Gather additional context to understand WHY this happened:

1. Recent changes: Was there a code deploy? Check git history if available
2. Data volume: Did data volume spike? Run a quick count on source tables
3. Upstream health: Did upstream tasks succeed but produce unexpected data?
4. Historical pattern: Is this a recurring failure? Check if same task failed before
5. Timing: Did this fail at an unusual time? (resource contention, maintenance windows)

Use af runs get <dag_id> <dag_run_id> to compare the failed run against recent successful runs.

On Astro

If you're running on Astro, these additional tools can help with diagnosis:

• Deployment activity log: Check the Astro UI for recent deploys — a failed deploy or recent code change is often the cause of sudden failures
• Astro alerts: Configure alerts in the Astro UI for proactive failure monitoring (DAG failure, task duration, SLA miss)
• Observability: Use the Astro observability dashboard to track DAG health trends and spot recurring issues

On OSS Airflow

• Airflow UI: Use the DAGs page, Graph view, and task logs to inspect recent runs and failures

Step 4: Provide Actionable Output

Structure your diagnosis as:

Root Cause

What actually broke? Be specific - not "the task failed" but "the task failed because column X was null in 15% of rows when the code expected 0%".

Impact Assessment

• What data is affected? Which tables didn't get updated?
• What downstream processes are blocked?
• Is this blocking production dashboards or reports?

Immediate Fix

Specific steps to resolve RIGHT NOW:

1. If it's a data issue: SQL to fix or skip bad records
2. If it's a code issue: The exact code change needed
3. If it's infra: Who to contact or what to restart

Prevention

How to prevent this from happening again:

• Add data quality checks?
• Add better error handling?
• Add alerting for edge cases?
• Update documentation?

Quick Commands

Provide ready-to-use commands:

• To clear and rerun the entire DAG run: af runs clear <dag_id> <run_id>
• To clear and rerun specific failed tasks: af tasks clear <dag_id> <run_id> <task_ids> -D
• To delete a stuck or unwanted run: af runs delete <dag_id> <run_id>