--- name: spark-executor-mcp-operate description: Operation guide for the spark-executor-mcp service — 16 MCP tools that submit, monitor, fetch logs from, and kill PySpark jobs on YARN, plus connection-profile and script-file management. USE THIS SKILL whenever the user wants to do anything with the spark-executor-mcp MCP service: submit a Spark/PySpark job to YARN, check job status or result, fetch container logs, kill a running job, save/list/get/delete a YARN connection, or write/read/update a PySpark script file. Also use it when the user asks generally about Spark, YARN, pyspark, cluster jobs, or distributed compute via this service. Do NOT guess tool names or invent a submit flow — read this skill first to learn the two-step prepare/confirm flow, the dual-ID contract (job_id vs application_id), and the SQL guard / path restrictions. The MCP service does NOT generate PySpark code — the calling LLM writes the code, then uses `write_job_file` to persist it on disk before submitting. --- # spark-executor-mcp 操作指南 Spark-executor-mcp is an MCP (Model Context Protocol) service that exposes **16 tools** for managing PySpark jobs on YARN. It runs as a FastAPI app mounted at `/spark-executor-mcp`; clients (typically LLM agents) call the tools via the standard MCP `tools/call` flow. This skill is the canonical reference for an LLM agent using the service. It does **not** describe implementation details — for that, see the source in `spark_executor/`. --- ## 0. Mindset before you start Three things you MUST internalize before calling any tool: 1. **The submit flow is two-step: `prepare_submit_job` then `confirm_submit_job`.** Prepare is cheap and reversible (just snapshots params + writes JSON to disk). Confirm is irreversible — it actually invokes `spark-submit` and a YARN application starts running. Never skip the prepare step, even when the user is in a hurry. 2. **Every Job has two IDs that are NOT interchangeable everywhere.** - `job_id` — local, 12-char hex (`a1b2c3d4e5f6`), generated by the service. Used for: looking up the Job record, all MCP tool calls. - `application_id` — YARN's own ID (`application_17400000001_0001`). Used for: YARN UI, `tracking_url`, the YARN REST API. The service's 4 job-lifecycle tools accept **either** ID (after the 2026-06-29 fix), but other systems (YARN UI, kubectl-style scripts) only know `application_id`. **Always store both** from every `confirm_submit_job` response. 3. **The LLM writes the PySpark code. The MCP service writes the file.** `write_job_file` is a file writer with SQL-safety checks, not a code generator. You compose the code in your context, then call `write_job_file(code=...)` to drop it on the container's filesystem where `spark-submit` can see it. --- ## 1. Tool index | Operation ID | HTTP | Group | Purpose | |---|---|---|---| | `save_connection` | POST | Connection | Upsert a named YARN connection (master, deploy_mode, spark_conf, …) | | `list_connections` | POST | Connection | List all saved connections | | `get_connection` | POST | Connection | Fetch one connection by name | | `delete_connection` | POST | Connection | Delete a connection by name | | `write_job_file` | POST | Job file | Write LLM-written PySpark code to disk | | `read_job_file` | POST | Job file | Read a script file back (capped at 1 MB) | | `update_job_file` | POST | Job file | Overwrite a script file (capped at 1 MB) | | `prepare_submit_job` | POST | Submit | Snapshot a job to `PendingSubmission`; **does NOT submit** | | `confirm_submit_job` | POST | Submit | Actually invoke `spark-submit` for a `pending_id` | | `update_pending_job` | POST | Submit | Edit a `PENDING` submission (script_path, queue, …) | | `cancel_pending_job` | POST | Submit | Cancel a `PENDING` submission | | `list_pending_jobs` | POST | Submit | List every PendingSubmission regardless of status | | `get_pending_job` | POST | Submit | Fetch one PendingSubmission by id | | `get_job_status` | POST | Job lifecycle | Query YARN for a job's live state (RUNNING / SUCCEEDED / …) | | `get_job_result` | POST | Job lifecycle | Terminal-oriented view: final_status, diagnostics, timing | | `get_job_logs` | POST | Job lifecycle | Aggregated container logs (default last 5000 chars) | | `kill_job` | POST | Job lifecycle | PUT state=KILLED to YARN REST for the app | (Total: 16 MCP tools + `/health` GET, which is not exposed as a tool.) --- ## 2. The canonical happy path: submit a PySpark job ``` 1. save_connection # one-time, per cluster 2. write_job_file # write the LLM's PySpark to disk 3. read_job_file # (optional) sanity-check what was written 4. prepare_submit_job # snapshot + persist; no YARN call yet 5. confirm_submit_job # NOW spark-submit runs 6. get_job_status / logs # poll while running 7. get_job_result # terminal view when done ``` ### 2.1 Save a connection (one-time per cluster) ```python save_connection( name="prod", master="yarn", deploy_mode="cluster", yarn_rm_url="http://rm.example.com:8088", spark_conf={"spark.sql.shuffle.partitions": "200"}, # optional: auth_type="kerberos", ssl_verify=False, ... ) ``` **`name`** is the lookup key — keep it short and stable. Re-calling `save_connection` with the same `name` overwrites; the original `yarn_rm_url` and `spark_conf` are **snapshot into the PendingSubmission at prepare time** and survive later edits to the connection (this is intentional — the user can re-point the connection at a different cluster without retargeting in-flight submissions). ### 2.2 Write the script to disk The LLM writes the PySpark code. Then: ```python script_path = write_job_file(code=PYSPARK_SOURCE)["script_path"] # Returns {"script_path": "/absolute/path/in/container.py", "bytes": N} ``` The path lives inside the container's `SPARK_EXECUTOR_JOBS_DIR` (default `./data/jobs/`). For pre-existing scripts on the host, mount the host directory into the container and skip this step — pass the in-container path directly to `prepare_submit_job`. ### 2.3 Prepare (snapshot, no YARN call) ```python prepare_submit_job( connection="prod", script_path=script_path, app_name="daily-aggregation", # REQUIRED, no default queue="default", # these 4 must be explicit executor_memory="2G", executor_cores=2, num_executors=2, # extra_args={"jars": "hdfs://...jar"}, # optional ) # Returns {"pending_id": "p_a1b2c3", "status": "PENDING", "parameters": {...}} ``` **You MUST pass `queue`, `executor_memory`, `executor_cores`, `num_executors` explicitly every time** — even though defaults exist server-side, the service rejects implicit defaults with a 400 listing the assumed values. This forces the agent (or the human reviewer) to see and approve what will actually be submitted. The response is the only chance to capture the `pending_id` you need for `confirm_submit_job`. Store it. ### 2.4 (Optional) Edit before submit If something needs to change between prepare and confirm: ```python update_pending_job( pending_id="p_a1b2c3", queue="research", # script_path can also be changed — but the new file MUST exist # and pass the SQL guard ) ``` Refuses to edit anything that is no longer `PENDING`. ### 2.5 Confirm (the irreversible step) ```python result = confirm_submit_job(pending_id="p_a1b2c3") # Returns {"job_id": "a1b2c3d4e5f6", # "application_id": "application_17400000001_0001", # "tracking_url": "http://rm:8088/proxy/application_17400000001_0001/"} ``` **STORE BOTH IDS NOW.** Future calls to `get_job_status` / `get_job_logs` / `kill_job` accept either, but `application_id` is the one YARN itself recognizes. `confirm_submit_job` is **idempotent** on `SUBMITTED` (re-calling returns the same record) and **retries** on transient `SparkSubmitError` (3 attempts with 5 s delay by default). It transitions to `FAILED` only after all retries are exhausted. ### 2.6 Monitor / fetch / kill ```python # While running state = get_job_status(job_id="a1b2c3d4e5f6").state logs = get_job_logs(job_id="a1b2c3d4e5f6", tail_chars=10000) # When done result = get_job_result(job_id="a1b2c3d4e5f6") # result.state -> "SUCCEEDED" / "FAILED" / "KILLED" / ... # result.final_status -> "SUCCEEDED" / "FAILED" / "KILLED" / "UNDEFINED" # result.diagnostics -> YARN's "why" string (often empty on success) # result.tracking_url -> the same proxy URL confirm_submit_job returned # To stop it kill_job(job_id="a1b2c3d4e5f6") ``` All four accept **either** `job_id` or `application_id`. Pass whichever you have on hand; the service tries `job_id` first, falls back to `application_id`. --- ## 3. The PendingSubmission state machine ``` prepare_submit_job | v +-------+ cancel_pending_job |PENDING+----------> CANCELLED (terminal) +---+---+ | confirm_submit_job v +----------+ | SUBMITTED| (terminal — kill via kill_job, not cancel) +----------+ (or) +--------+ | FAILED | <-- confirm_submit_job exhausted retries +--------+ | confirm_submit_job (resets to PENDING, retries) v PENDING ``` - `cancel_pending_job` **refuses** to cancel `SUBMITTED` or `FAILED` records — those are terminal; use `kill_job` instead. - `update_pending_job` **refuses** to edit anything that is not `PENDING`. - `confirm_submit_job` on a `SUBMITTED` record is a no-op (returns the same `job_id` / `application_id`). On a `FAILED` record, it resets to `PENDING` and retries. On a `CANCELLED` record, it raises 400. --- ## 4. The dual-ID contract | ID | Where it comes from | What it's good for | |---|---|---| | `job_id` | service-generated, 12-char hex (`a1b2c3d4e5f6`) | Looking up the Job in this service's store; all 4 lifecycle tools | | `application_id` | parsed from `spark-submit` stderr (`application__`) | YARN UI, YARN REST, `tracking_url`, talking to ops scripts | **Both IDs are returned by `confirm_submit_job`.** Both are accepted by `get_job_status` / `get_job_result` / `get_job_logs` / `kill_job`. **You don't need to remember which to pass — but DO remember to store both from the confirm response** because: - If the Job store has been wiped (rare; only on data dir loss), only `application_id` is still meaningful to YARN — you can't poll a YARN app you can't identify. - If you're going to paste a link to a teammate, `tracking_url` (derived from `application_id`) is the human-friendly form. If a lifecycle tool returns `KeyError("No Job found for id='X' …")`, check that `X` came from a successful `confirm_submit_job` response. The error message intentionally mentions both ID forms and shows an example of each so you can self-diagnose. --- ## 5. Connection profiles `Connection` is the cluster profile — it's the "where to submit" record. Fields: | Field | Required | Default | Notes | |---|---|---|---| | `name` | yes | — | The lookup key | | `master` | yes | `"yarn"` | `"yarn"` / `"spark://…"` / `"k8s://…"` / `"local[N]"` | | `deploy_mode` | yes | `"cluster"` | `"cluster"` or `"client"` | | `yarn_rm_url` | no | env `YARN_RESOURCE_MANAGER_URL` | Required if you'll call `get_job_status` / `get_job_logs` / `kill_job` (the lifecycle tools need a YARN endpoint) | | `spark_conf` | no | `{}` | Merged into `spark-submit --conf` at submit time | | `ssl_verify` | no | env `SPARK_EXECUTOR_SSL_VERIFY_DEFAULT` | bool | | `ssl_ca_bundle` | no | env `SPARK_EXECUTOR_SSL_CA_BUNDLE_DEFAULT` | Path to CA file | | `auth_type` | no | `"none"` | `"none"` / `"simple"` / `"basic"` / `"kerberos"` | | `auth_user` / `auth_password` | for `basic` | — | | | `auth_principal` / `auth_keytab` | for `kerberos` (display only) | — | Real auth uses the system cache | **Snapshot semantics:** when `prepare_submit_job` runs, it copies `master` / `deploy_mode` / `spark_conf` / `yarn_rm_url` from the **current** Connection into the `PendingSubmission`. Editing the Connection later does **not** retarget an in-flight submission. **Lifecycle tools use the Job's snapshotted `yarn_rm_url`** (set at confirm time) — not the Connection's current value. If the RM moves between confirm and a follow-up `get_job_logs`, you have a problem; re-pointing the Connection does not help. --- ## 6. Job file workflow (`write_job_file` / `read_job_file` / `update_job_file`) These are **filesystem I/O tools, not code generators**. The LLM in context writes the PySpark code; these tools just persist it where `spark-submit` can find it, with safety guards. **Typical lifecycle:** ``` LLM composes code --> write_job_file(code=...) # write LLM reviews code --> read_job_file(script_path=...) # verify LLM revises code --> update_job_file(script_path=..., # overwrite content=...) LLM submits --> prepare_submit_job(script_path=...) ``` **Guards (these are why the tools exist instead of just `cat > file.sh`):** - **SQL guard** — `write_job_file` and `update_job_file` both reject code containing forbidden SQL (DROP, DELETE, UPDATE, TRUNCATE, ALTER, GRANT, REVOKE, …). The check is conservative; if it false-positives, rewrite to use only SELECT/INSERT or restructure. - **Path restriction** — `update_job_file` only writes under `SPARK_EXECUTOR_JOBS_DIR`. This blocks accidentally overwriting host-mounted configs or the service's own files. - **Size cap** — 1 MB on both `read_job_file` and `update_job_file`. Use `read_job_file` for small scripts; for huge ones, mount the host directory and skip these tools. **For pre-existing scripts on the host:** mount the host dir into the container (e.g. `-v /host/scripts:/app/scripts:ro` in `docker run`) and pass the in-container path directly to `prepare_submit_job` — no need to round-trip through the file tools. --- ## 7. Error reference | Status | When | What to do | |---|---|---| | 400 | `prepare_submit_job` without explicit defaults; `cancel_pending_job` on terminal state; `update_pending_job` on non-PENDING; `prepare_submit_job` with missing/non-file `script_path`; SQL policy violation | Read the message — it almost always names the fix. Re-submit with corrected args. | | 404 | `KeyError` from tool layer: unknown `connection`, `pending_id`, `job_id`, or `application_id` | The ID you sent doesn't match anything in the store. For lifecycle tools, the error message explicitly suggests both ID forms. | | 422 | Pydantic validation: missing field, wrong type | Usually a typo or missing required arg. The response body lists every field error. | | 500 | spark-submit subprocess failed and was not a `SparkSubmitError` (e.g. binary missing); YARN REST call failed | The tool logs the full traceback to `data/logs/error/...` — check there. | The service translates exceptions at the FastAPI layer: - `KeyError` → 404 (with the KeyError's string as `detail`) - `ValueError` → 400 - Pydantic validation → 422 So when the server returns 404, the body `detail` field is the same "Unknown job_id: …" / "Unknown connection: …" string the tool layer raised. --- ## 8. Common pitfalls | Pitfall | Why it bites | What to do | |---|---|---| | Skipping the prepare step | `confirm_submit_job` requires a `pending_id`; calling it without one returns 400 | Always prepare first | | Passing implicit defaults | Server returns 400 listing what you didn't confirm | Pass `queue`, `executor_memory`, `executor_cores`, `num_executors` every time | | `script_path` doesn't exist in the container | `prepare_submit_job` returns 400; the agent generated the path in its own context but the container's filesystem is different | Either call `write_job_file` first, or mount a host dir | | SQL injection in the script | `write_job_file` / `update_job_file` / `prepare_submit_job` all 400 | Only use SELECT/INSERT; never DROP/DELETE/UPDATE | | `cancel_pending_job` on a running YARN app | Returns 400 — submissions are terminal once submitted | Use `kill_job(job_id=...)` instead, which talks to YARN REST | | Re-pointing a Connection and expecting in-flight jobs to follow | They don't — the Job snapshots `yarn_rm_url` at confirm time | Re-issue with a new `prepare_submit_job` if you actually need a different RM | | Calling lifecycle tools with the wrong ID type | Used to fail; **fixed in the 2026-06-29 update** — both IDs are accepted | Just pass whichever you have; the service tries `job_id` first | | "Session not found" at the MCP layer | Multi-worker gunicorn + in-process session state | Out of scope for this skill; the service warns on startup if `GUNICORN_WORKERS>1`; set `GUNICORN_WORKERS=1` or front with a sticky LB | --- ## 9. End-to-end example (LLM agent's perspective) User: "Run a word count on `s3a://my-bucket/books/*.txt` and write the result back to `s3a://my-bucket/wc/`." ``` # 1. Cluster profile (assumes this is a fresh setup) save_connection( name="prod", master="yarn", deploy_mode="cluster", yarn_rm_url="http://rm.prod.example.com:8088", spark_conf={ "spark.sql.shuffle.partitions": "200", "spark.hadoop.fs.s3a.access.key": "...", "spark.hadoop.fs.s3a.secret.key": "...", }, ) # 2. Compose the PySpark code IN YOUR CONTEXT pyspark_code = ''' from pyspark.sql import SparkSession spark = SparkSession.builder.appName("wordcount").getOrCreate() sc = spark.sparkContext files = sc.wholeTextFiles("s3a://my-bucket/books/") words = files.flatMap(lambda f: f[1].lower().split()) \\ .map(lambda w: (w, 1)) \\ .reduceByKey(lambda a, b: a + b) df = words.toDF(["word", "count"]) df.write.mode("overwrite").parquet("s3a://my-bucket/wc/") ''' # 3. Persist to disk script_path = write_job_file(code=pyspark_code)["script_path"] # 4. Sanity-check (optional but recommended) contents = read_job_file(script_path=script_path)["content"] # ... review in context ... # 5. Prepare (snapshot — no YARN call yet) pending = prepare_submit_job( connection="prod", script_path=script_path, app_name="wordcount-books", queue="default", executor_memory="2G", executor_cores=2, num_executors=2, ) pending_id = pending["pending_id"] # 6. Confirm (NOW spark-submit runs) result = confirm_submit_job(pending_id=pending_id) job_id = result["job_id"] # STORE application_id = result["application_id"] # STORE tracking_url = result["tracking_url"] # STORE # 7. Poll import time while True: st = get_job_status(job_id=job_id).state if st in ("SUCCEEDED", "FAILED", "KILLED", "FINISHED"): break time.sleep(30) # 8. Final result res = get_job_result(job_id=job_id) print(res.final_status, res.diagnostics) # If something went wrong and you want to see why: # logs = get_job_logs(job_id=job_id, tail_chars=20000) ``` --- ## 10. Reference paths (for the curious) This skill is the **operation** guide. The architectural / implementation details live in: - `CLAUDE.md` — project conventions, persistence layout, two-step submit rationale, MCP arg pattern, MCP session affinity caveat. - `docs/superpowers/plans/2026-06-24-spark-executor-mcp.md` — the original implementation plan with Stage 1 / 2 / 3 breakdown. - `spark_executor/server.py` — the route + exception-handler layer. - `spark_executor/tools/requests.py` — the Pydantic body models; useful to read when the MCP 422 response confuses you. - `spark_executor/core/job_store.py` — Job persistence; explains the dual-ID contract and the file-backed JSON layout.