--- name: prefect-7049750f2663 description: >- Prefect is a Python workflow orchestration framework that turns functions into observable, retryable, schedulable data pipelines. Use when asked to "orchestrate a Python pipeline", "schedule a flow with cron", "add retries and caching to tasks", "deploy a Prefect flow", "run a worker" or "alert when a flow fails". Covers Prefect 3.x flows and tasks, cache policies, flow.serve, work pools with workers, the prefect deploy CLI, blocks, variables and failure hooks. license: Apache-2.0 compatibility: "Python 3.11-3.15; prefect 3.x (tested with 3.9.0); Linux, macOS, Windows" metadata: author: terminal-skills version: "1.1.0" category: data-ai tags: "prefect, workflow-orchestration, python, data-pipeline, scheduling" repository: https://github.com/PrefectHQ/prefect --- # Prefect ## Overview Prefect 3 turns Python functions into flows (`@flow`) made of tasks (`@task`), with retries, caching, logging, a UI and scheduled deployments. Two ways to run on a schedule: `flow.serve(...)` starts one long-running process that executes runs itself, and work pools plus workers (`prefect deploy` and `prefect worker start`) execute runs in managed infrastructure. Agents and `prefect.deployments.Deployment` from Prefect 2 are removed: importing `Deployment` raises an error. ## Instructions ### Install and run a server ```bash python3 -m venv .venv && source .venv/bin/activate pip install prefect httpx # needs Python 3.11 or newer prefect version prefect server start # UI and API at http://127.0.0.1:4200 # In another shell, point clients at it: prefect config set PREFECT_API_URL=http://127.0.0.1:4200/api ``` Running a flow without any server also works: Prefect starts a temporary local server for the run. For Prefect Cloud use `prefect cloud login`. ### Flows and tasks ```python # flows/orders_etl.py from datetime import timedelta import httpx from prefect import flow, task, get_run_logger from prefect.cache_policies import INPUTS from prefect.tasks import exponential_backoff @task(retries=3, retry_delay_seconds=exponential_backoff(backoff_factor=10), retry_jitter_factor=0.5, timeout_seconds=120) def fetch_orders(day: str) -> list[dict]: r = httpx.get("https://api.northwind-shop.dev/orders", params={"date": day}, timeout=30) r.raise_for_status() return r.json()["results"] @task(cache_policy=INPUTS, cache_expiration=timedelta(hours=1)) def to_cents(order: dict) -> dict: return {"id": order["id"], "cents": round(order["amount"] * 100)} @task def load(rows: list[dict]) -> int: get_run_logger().info("loading %d rows", len(rows)) return len(rows) @flow(name="orders-etl", log_prints=True) def orders_etl(day: str = "2026-10-23") -> int: orders = fetch_orders(day) rows = [f.result() for f in to_cents.map(orders)] # runs the tasks concurrently count = load(rows) print(f"loaded {count} rows") return count if __name__ == "__main__": orders_etl() ``` Key points: `retry_delay_seconds` takes a number, a list (one delay per retry) or `exponential_backoff(...)`. Caching is configured with `cache_policy` (`INPUTS`, `TASK_SOURCE`, `DEFAULT`, from `prefect.cache_policies`); the old `task_input_hash` import is deprecated. `task.submit(...)` and `task.map(...)` return futures; call `.result()` or `wait(futures)` from `prefect.futures`. Tasks and flows may be `async def`; use `await` or `asyncio.gather` inside an async flow. ### Schedule with `flow.serve` Simplest deployment: one Python process that stays running and executes scheduled and manual runs. ```python # flows/daily_report.py from prefect import flow @flow(log_prints=True) def daily_report(region: str = "emea"): print(f"report for {region}") if __name__ == "__main__": daily_report.serve(name="daily-report", cron="0 8 * * *", tags=["reporting"], parameters={"region": "emea"}) ``` Run `python flows/daily_report.py` (keep it alive with systemd or a container), then trigger a run manually: ```bash prefect deployment run "daily-report/daily-report" --param region=apac --watch prefect deployment ls ``` `serve` also accepts `interval` (seconds or `timedelta`), `rrule`, `schedules`, `paused` and `limit` (concurrent runs). ### Work pools, workers and `prefect deploy` Use this when runs must execute on separate infrastructure (Docker, Kubernetes, cloud). ```bash prefect work-pool create etl-process --type process prefect deploy flows/orders_etl.py:orders_etl --name etl-prod --pool etl-process --cron "*/30 * * * *" prefect worker start --pool etl-process prefect deployment run "orders-etl/etl-prod" --param day=2026-10-22 ``` `prefect deploy` also accepts `--interval`, `--tag`, `--param` and `--job-variable`, and can save the deployment definition to `prefect.yaml` (`prefect init` creates one); without that file it deploys straight from the command-line options. There is no default pool called `default-agent-pool`: create a pool first. Workers need access to the flow's source code, so use a shared path, a Git source (`flow.from_source(...).deploy(...)` in Python) or a built image. Read logs with `prefect flow-run logs ` and list runs with `prefect flow-run ls`. ### Secrets, variables and failure alerts ```python # flows/with_config.py from prefect import flow from prefect.blocks.system import Secret from prefect.blocks.notifications import SlackWebhook from prefect.variables import Variable def alert_slack(flow, flow_run, state): SlackWebhook.load("ops-alerts").notify(f"Flow {flow.name} run {flow_run.name} ended {state.type.value}") @flow(on_failure=[alert_slack]) def sync_stripe(): api_key = Secret.load("stripe-api-key").get() batch_size = Variable.get("stripe_batch_size", default="500") ... ``` Create the blocks once, in the UI (Blocks page) or in Python (`Secret(value=os.environ["STRIPE_API_KEY"]).save("stripe-api-key")`). `on_failure` and `on_completion` are hook lists on flows and tasks; `on_crashed` and `on_cancellation` exist on flows only. Automations in the UI (trigger: flow run failed, action: send notification) work without code. Integration blocks such as SQLAlchemy live in separate packages (`pip install prefect-sqlalchemy`, then `prefect block register -m prefect_sqlalchemy`). ## Examples ### Example 1: "Run my ETL every 30 minutes and retry the API call" Save `flows/orders_etl.py` from above, start `prefect server start`, then `python -c "from flows.orders_etl import orders_etl; orders_etl.serve(name='etl-prod', cron='*/30 * * * *')"` from the project root. The UI shows a scheduled run every half hour; a failed `fetch_orders` is retried up to three times with growing delays before the flow run is marked Failed. ### Example 2: "Page the team when the nightly job fails" Create a `SlackWebhook` block named `ops-alerts` in the UI with the webhook URL, add the `on_failure=[alert_slack]` hook from the previous section, deploy with `prefect deploy ... --cron "0 2 * * *"`. When a run fails, the hook posts the flow and run name to Slack. ## Guidelines - Pin the major version (`prefect>=3,<4`); Prefect 2 code using agents, `Deployment.build_from_flow` or `task_input_hash` as the main cache needs migration. - Keep secrets in Secret blocks or environment variables, never in flow parameters, which appear in the UI. - Bind the server to `127.0.0.1` (the default for local use) unless it sits behind authentication; the open-source server has no built-in login. - Make tasks idempotent: a retry or a re-run repeats side effects such as inserts. - Do not put large datasets through task return values; write to storage and pass paths. - Workers pick up runs only for the pool they poll; a run stuck in Late or Pending usually means no worker is running for that pool. --- Source attribution: TerminalSkills Original project: https://github.com/TerminalSkills/skills/blob/3bfbf7f76459d89422eddc0e5f572ad0e6c393c9/skills/prefect/SKILL.md License: Apache-2.0 License information: https://www.apache.org/licenses/LICENSE-2.0 Original upstream instructions; downloaded from Mega AI Hub. ## Upstream license notice Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. Definitions. "License" shall mean the terms and conditions for use, reproduction, and distribution as defined by Sections 1 through 9 of this document. "Licensor" shall mean the copyright owner or entity authorized by the copyright owner that is granting the License. "Legal Entity" shall mean the union of the acting entity and all other entities that control, are controlled by, or are under common control with that entity. For the purposes of this definition, "control" means (i) the power, direct or indirect, to cause the direction or management of such entity, whether by contract or otherwise, or (ii) ownership of fifty percent (50%) or more of the outstanding shares, or (iii) beneficial ownership of such entity. "You" (or "Your") shall mean an individual or Legal Entity exercising permissions granted by this License. "Source" form shall mean the preferred form for making modifications, including but not limited to software source code, documentation source, and configuration files. "Object" form shall mean any form resulting from mechanical transformation or translation of a Source form, including but not limited to compiled object code, generated documentation, and conversions to other media types. "Work" shall mean the work of authorship, whether in Source or Object form, made available under the License, as indicated by a copyright notice that is included in or attached to the work (an example is provided in the Appendix below). "Derivative Works" shall mean any work, whether in Source or Object form, that is based on (or derived from) the Work and for which the editorial revisions, annotations, elaborations, or other modifications represent, as a whole, an original work of authorship. For the purposes of this License, Derivative Works shall not include works that remain separable from, or merely link (or bind by name) to the interfaces of, the Work and Derivative Works thereof. "Contribution" shall mean any work of authorship, including the original version of the Work and any modifications or additions to that Work or Derivative Works thereof, that is intentionally submitted to the Licensor for inclusion in the Work by the copyright owner or by an individual or Legal Entity authorized to submit on behalf of the copyright owner. For the purposes of this definition, "submitted" means any form of electronic, verbal, or written communication sent to the Licensor or its representatives, including but not limited to communication on electronic mailing lists, source code control systems, and issue tracking systems that are managed by, or on behalf of, the Licensor for the purpose of discussing and improving the Work, but excluding communication that is conspicuously marked or otherwise designated in writing by the copyright owner as "Not a Contribution." "Contributor" shall mean Licensor and any individual or Legal Entity on behalf of whom a Contribution has been received by the Licensor and subsequently incorporated within the Work. 2. Grant of Copyright License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare Derivative Works of, publicly display, publicly perform, sublicense, and distribute the Work and such Derivative Works in Source or Object form. 3. Grant of Patent License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use, offer to sell, sell, import, and otherwise transfer the Work, where such license applies only to those patent claims licensable by such Contributor that are necessarily infringed by their Contribution(s) alone or by combination of their Contribution(s) with the Work to which such Contribution(s) was submitted. If You institute patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Work or a Contribution incorporated within the Work constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed. 4. Redistribution. You may reproduce and distribute copies of the Work or Derivative Works thereof in any medium, with or without modifications, and in Source or Object form, provided that You meet the following conditions: (a) You must give any other recipients of the Work or Derivative Works a copy of this License; and (b) You must cause any modified files to carry prominent notices stating that You changed the files; and (c) You must retain, in the Source form of any Derivative Works that You distribute, all copyright, patent, trademark, and attribution notices from the Source form of the Work, excluding those notices that do not pertain to any part of the Derivative Works; and (d) If the Work includes a "NOTICE" text file as part of its distribution, then any Derivative Works that You distribute must include a readable copy of the attribution notices contained within such NOTICE file, excluding any notices that do not pertain to any part of the Derivative Works, in at least one of the following places: within a NOTICE text file distributed as part of the Derivative Works; within the Source form or documentation, if provided along with the Derivative Works; or, within a display generated by the Derivative Works, if and wherever such third-party notices normally appear. The contents of the NOTICE file are for informational purposes only and do not modify the License. You may add Your own attribution notices within Derivative Works that You distribute, alongside or as an addendum to the NOTICE text from the Work, provided that such additional attribution notices cannot be construed as modifying the License. You may add Your own copyright statement to Your modifications and may provide additional or different license terms and conditions for use, reproduction, or distribution of Your modifications, or for any such Derivative Works as a whole, provided Your use, reproduction, and distribution of the Work otherwise complies with the conditions stated in this License. 5. Submission of Contributions. Unless You explicitly state otherwise, any Contribution intentionally submitted for inclusion in the Work by You to the Licensor shall be under the terms and conditions of this License, without any additional terms or conditions. Notwithstanding the above, nothing herein shall supersede or modify the terms of any separate license agreement you may have executed with Licensor regarding such Contributions. 6. Trademarks. This License does not grant permission to use the trade names, trademarks, service marks, or product names of the Licensor, except as required for reasonable and customary use in describing the origin of the Work and reproducing the content of the NOTICE file. 7. Disclaimer of Warranty. Unless required by applicable law or agreed to in writing, Licensor provides the Work (and each Contributor provides its Contributions) on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. You are solely responsible for determining the appropriateness of using or redistributing the Work and assume any risks associated with Your exercise of permissions under this License. 8. Limitation of Liability. In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall any Contributor be liable to You for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising as a result of this License or out of the use or inability to use the Work (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if such Contributor has been advised of the possibility of such damages. 9. Accepting Warranty or Additional Liability. While redistributing the Work or Derivative Works thereof, You may choose to offer, and charge a fee for, acceptance of support, warranty, indemnity, or other liability obligations and/or rights consistent with this License. However, in accepting such obligations, You may act only on Your own behalf and on Your sole responsibility, not on behalf of any other Contributor, and only if You agree to indemnify, defend, and hold each Contributor harmless for any liability incurred by, or claims asserted against, such Contributor by reason of your accepting any such warranty or additional liability. END OF TERMS AND CONDITIONS Copyright 2025 Terminal Skills Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. # Mega AI Hub resource metadata Creator / publisher: TerminalSkills Original project: https://github.com/TerminalSkills/skills/blob/3bfbf7f76459d89422eddc0e5f572ad0e6c393c9/skills/prefect/SKILL.md Attribution basis: Source repository record Fields of work: Development & Engineering, Product Management Roles: Data Engineer, ML / AI Engineer, Product Manager Specialties: API, Backend Tools: Prefect Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: 99ee697abc90db068f99cb0d2e75d8253abc2340d60d7dad990ed42a1b492e2c