create-dag

name	create-dag
description	Generates an Airflow DAG from the LLD artifact and pipeline configs. Reads the approved LLD from outputs/, applies DAG templates, and writes a production-ready DAG file to airflow/dags/. Also known as: dag generation, pipeline scaffolding, airflow pipeline creation. Input formats: LLD markdown, DAG config YAML. Output format: Python DAG file (.py). Use when the user asks to: - Create, generate, or scaffold an Airflow DAG - Translate an LLD into a runnable pipeline - Build a DAG for bronze/silver/gold layers
argument-hint	[lld-path]
allowed-tools	Read, Write, Edit, Grep, Glob, Bash, AskUserQuestion, Skill
context	fork

Create Airflow DAG

You are a senior Data Engineer specialising in Apache Airflow. Your job is to translate the approved Low-Level Design (LLD) artifact into a production-ready Airflow DAG.

Workspace Discovery

Before any file operation, run the discovery helper and substitute the returned tokens into every path this skill reads, writes, or edits:

python3 ${CLAUDE_PLUGIN_ROOT}/skills/validate-stories/scripts/status_rollup.py --mode discover

The JSON output supplies {workspace_root}, {project_root}, {project_name}, {stories_dir}, and {learnings_queue}. The plugin is project-agnostic — never hardcode project or chapter names in edits.

Coding Patterns & Libraries Handbook

Before generating a DAG, load the latest coding-patterns handbook:

PATTERNS_DIR=$(ls -d "{workspace_root}/inputs/code/v"* 2>/dev/null | sort -V | tail -1)
if [ -z "$PATTERNS_DIR" ] || [ ! -d "$PATTERNS_DIR" ]; then
  echo "CRITICAL: inputs/code/v*/ not found. Run /developer-plugin:refresh-libraries to initialize the library cache."
  exit 1
fi
LIBRARIES_FILE="$PATTERNS_DIR/LIBRARIES.md"

Required pattern docs for this skill:

• $PATTERNS_DIR/airflow-dag-pattern.md — factory, TaskGroup, SparkSubmitOperator defaults
• $PATTERNS_DIR/naming-conventions.md — DAG file name, task IDs
• $PATTERNS_DIR/LIBRARIES.md — pinned Airflow + provider versions

Library freshness check

LAST_VERIFIED=$(grep '^last_verified:' "$LIBRARIES_FILE" | awk '{print $2}')
TODAY=$(date -u +%Y-%m-%d)
AGE_DAYS=$(python3 -c "from datetime import date; print((date.fromisoformat('$TODAY') - date.fromisoformat('$LAST_VERIFIED')).days")

If AGE_DAYS > 30, pause and call AskUserQuestion with options Refresh now / Proceed with cached versions / Cancel. On Refresh, invoke /developer-plugin:refresh-libraries then resume.

References trailer (in output)

Emit a ### References section citing consumed pattern docs + LIBRARIES.md vintage. Add a stale-cache warning if the user proceeded with cached versions.

Phase 0.a — Argument Resolution (mandatory, runs first)

The Skill-tool argument frequently fails to reach forked subagents. Resolve the target via the shared resolver, which checks four sources in order: $SKILL_ARG → {workspace_root}/.skill-arg → conversational arg → auto-mode.

# Step 1: capture the user's conversational input. Substitute the
# bracketed text below with the EXACT message the user supplied after
# the skill name; if no message was supplied, leave it as an empty
# string. This is the ONLY substitution this skill requires.
CONV_ARG='<<EXACT_CONVERSATIONAL_TEXT_FROM_USER_OR_EMPTY_STRING>>'

# Step 2: run the shared resolver. It auto-discovers the workspace
# from $PWD, so no {workspace_root} substitution is required. Output is
# two lines on stdout: the resolved value, then the source token.
read -r RESOLVED_ARG RESOLVED_SOURCE < <(
  bash "${CLAUDE_PLUGIN_ROOT}/scripts/resolve_skill_arg.sh" "$CONV_ARG" \
    | paste -sd' ' -
)

Print this banner as the first line of skill output:

RESOLVED TARGET: <value> (source: <SKILL_ARG | .skill-arg | conversational | __AUTO__>)

If $RESOLVED_SOURCE == EMPTY, fall through to the skill's existing clarification step (typically AskUserQuestion). DO NOT ask the user before running this resolver.

Workflow

Phase 0: Upstream Gate

Resolve upstream versions via the shared helper (uses outputs/dev-lock.yaml when present, otherwise falls back to latest v{N}):

eval "$(python3 ${CLAUDE_PLUGIN_ROOT}/scripts/resolve_versions.py --export)"
LATEST_LLD_DIR="${LATEST_LLD_DIR:-$(ls -d {workspace_root}/../chapter-4/outputs/lld/v* | sort -V | tail -1)}"

Read the latest LLD from $LATEST_LLD_DIR/ and verify Status: Approved. If not approved, stop and inform the user.

Phase 1: Read Inputs

• Latest LLD markdown from {workspace_root}/../chapter-4/outputs/lld/v*/
• DAG config from {project_root}/airflow/configs/ if present
• Existing DAGs in {project_root}/airflow/dags/ for patterns

Phase 2: Clarify

Use AskUserQuestion to confirm:

• Target Airflow version and executor (LocalExecutor / CeleryExecutor / KubernetesExecutor)
• Schedule interval
• Retry and SLA settings
• Connection IDs to use

Phase 3: Generate DAG

• Follow the task dependency graph defined in the LLD ## Pipeline DAG section
• Use TaskGroup to group bronze / silver / gold stages
• Parameterise connections and paths via Airflow Variables or a config YAML
• Include docstring referencing the LLD section and artifact version
• CRITICAL — env-driven paths in every generated DAG file:
  • configs_dir = os.environ.get("AIRFLOW_CONFIGS_DIR", "/opt/airflow/configs")
  • application = os.environ.get("<TYPE>_RUNNER_APP", "/opt/airflow/jobs/run_<task_type>.py") per task type from LLD §4.2
  • Never emit application="run_local.py" (relative — breaks under /opt/airflow/)
  • Never emit configs_dir="airflow/configs" (relative — same issue)
  • The validator (DAG-PATHS-001, DAG-PATHS-002) rejects either pattern.
  • Reference snippet: inputs/code/v1/scripts/dag_factory.py.snippet.

Phase 3b: Generate per-task entry wrappers (MANDATORY)

SparkSubmitOperator.application is a path to a .py file, not a -m module spec. Spokane learned this when its wrapper failed at runtime with PermissionError: '-m'. To prevent recurrence, this skill auto-generates per-task entry shims under <project_root>/airflow/jobs/run_<task_type>.py from inputs/code/v1/scripts/run_layer_entrypoint.py.j2, one shim per distinct task type listed in LLD §4.2 task inventory.

Generation steps:

1. Parse LLD §4.2 task inventory. Extract the distinct task-type set (e.g. for the patient_360 LLD: bronze_ingestion, bronze_recon, silver_dim, silver_fact, gold_aggregate). Group rows that share a Type column — emit one wrapper per type, not per-row.
2. For each task type, resolve the runner contract. Read LLD §5 task table to extract Module Path (the dotted runner module) and the argv signature (typical args: --config-path, --ds, sometimes --layer, --table, --configs-dir). The runner's entry function is main by convention; if the LLD §2.3 contract names it differently, use that.
3. Render the Jinja template with these variables and write to <project_root>/airflow/jobs/run_<task_type>.py:

   from jinja2 import Environment, FileSystemLoader
   env = Environment(loader=FileSystemLoader(f"{workspace_root}/inputs/code/v1/scripts"))
   tmpl = env.get_template("run_layer_entrypoint.py.j2")
   for task_type, spec in task_types.items():
       (jobs_dir / f"run_{task_type}.py").write_text(tmpl.render(
           project=project_name,
           task_type=task_type,
           runner_module=spec["module"],
           entry_function=spec.get("entry", "main"),
           argv_spec=spec["argv"],
       ))
   

4. Emit env-var bindings in the airflow service of _infra/docker/docker-compose.yml. Each generated wrapper gets a <TYPE>_RUNNER_APP=/opt/airflow/jobs/run_<task_type>.py line in environment: so the DAG factory's application=os.environ["<TYPE>_RUNNER_APP"] lookup resolves at runtime. The current cookiecutter ships with BRONZE_RUNNER_APP and BRONZE_RECON_APP pre-wired; add others here when LLD §4.2 introduces new task types.
5. DAG factory consumes the env vars. Generated DAG files MUST resolve application from the <TYPE>_RUNNER_APP env var (not hardcode the path). See inputs/code/v1/scripts/dag_factory.py.snippet:_spark_task for the reference pattern.

Worked example — Bronze, two task types:

LLD §4.2 row	task_type	Wrapper file	Runner module	Compose env var
ingest_* (13 rows)	bronze_ingestion	airflow/jobs/run_bronze_ingestion.py	patient_360.bronze.ingestion_runner	BRONZE_RUNNER_APP
reconciliation_bronze	bronze_recon	airflow/jobs/run_bronze_recon.py	patient_360.bronze.reconciliation	BRONZE_RECON_APP

The DAG factory's _spark_task("ingest_patients", "bronze", "synthea_patients") call resolves application to os.environ["BRONZE_RUNNER_APP"] → /opt/airflow/jobs/run_bronze_ingestion.py → which imports patient_360.bronze.ingestion_runner.main(args).

Phase 4: Write Output

Save to {project_root}/airflow/dags/{dag_id}.py

Phase 5: Validate

Invoke /developer-plugin:validate-dag on the generated file. Fix any CRITICAL issues before finishing.

Phase 6: Verification Compliance Self-Check (MANDATORY before reporting OK)

The story's ## Verification block is the contract. After every prior phase has emitted its files, run the AC verifier against the target story and refuse to declare OK if any mechanical verifier still fails.

python3 ${CLAUDE_PLUGIN_ROOT}/../scripts/verify_acs.py STORY-NN-NNN --json

(For batch / multi-story dispatch, run once per story.)

Parse the JSON output. For each AC in acs[]:

• status == "FAIL" and at least one check has a non-manual kind that failed → emit one CRITICAL line per failing check: CRITICAL STORY-NN-NNN AC<N>: <check.spec> — <check.detail> Then stop. Do NOT mark the plan task done. Do NOT print the OK trailer. The orchestrator's Phase 2 Step 3.5 reads this and halts the story.
• status == "FAIL" but every failing check is manual: → INFO only (manual checks can't fail mechanically; treat as author note).
• status == "PASS" / INDETERMINATE → continue.
• has_verification == false → emit one WARNING line STORY-NN-NNN: no Verification block — generation completed without AC compliance check. Then continue.

This phase is the only place this skill flips its overall result from OK to FAILED. Skills that ignore it leave gaps the orchestrator cannot see.

Learnings & Corrections

Active Learnings

• L-001 (2026-05-11): Always: In Airflow 3.x, resolve the active DAG via airflow.sdk.definitions._internal.contextmanager.DagContext.get_current() and pass explicitly to factories rather than relying on contextual binding.
• L-002 (2026-05-12): Always: Dev DAG defaults: max_active_tasks=1 and catchup=False. Document that production raises these only after the SE stats table has been seeded by at least one successful run.
• L-003 (2026-05-12): Always: Any task that touches Spark must use SparkSubmitOperator (own JVM). PythonOperator with build_spark_session inside the callable is forbidden under Airflow 3.x.
• L-004 (2026-05-12): Always: Use 2-part FQNs (schema.table) throughout when spark_catalog is the default catalog. The catalog name (unity/spark_catalog) never appears in writer or query code; it is only relevant for catalog config.