Python + Poetry REST API with FastAPI, hosted on GCP

This template will get you ready to deploy a FastAPI app in Google Cloud with automatic API versioning by major release version and automatic custom domain mapping.

Major tags maintain separate API services in Cloud Run. For example, if my custom domain is, running the release GitHub action to create version v2.3.4 will update the v2 tag and automatically (re)-deploy to the service with the released code. The v1 service is unaffected, and there’s no need to keep v1-compatible code around in the default branch of your repo after bumping to v2. New v1 versions can be pushed separately to update that version using whatever workflow you want that produces a new v1.*.* semver tag, for example for bugfixes that affect the previous version. This keeps the maintenance cost of the code low while also ensuring old versions of the API are live and available to clients until they’re migrated to the newer versions.

Getting started from the template

  1. Rename the src/gcp_fastapi_poetry package.
  2. Globally replace (case-sensitive) instances of gcp-fastapi-poetry, gcp_fastapi_poetry, and GCP_FASTAPI_POETRY with your project and package name (including later in this list).
  3. Set your repo up on CodeCov and add a codecov token to your repo under the CODECOV_TOKEN secret.
  4. Create a new repo-scoped personal access token and add it as a DEPLOY_TOKEN repo secret. This is so we can maintain major version tags.
  5. Change your Cloud Run configuration in cloudbuild.yaml as appropriate. By default, it will deploy an API that can be invoked with no authentication.
  6. Configure a Cloud Build trigger in your GCP project to deploy from cloudbuild.yaml on a new tag that matches the regex ^(v(\d+))$, with a substituion variable _GCP_FASTAPI_POETRY_API_DOMAIN pointing to the (sub)-domain you want to host the API on. Make sure the cloudbuild service account has the required permissions (Cloud Build settings –> enable Cloud Run, Service Accounts, and Cloud Build) and is registered as an owner of your custom domain if required.
  7. Update as appropriate, making sure to retain the original copyright and permissions notices in your distribution according to the MIT license that this template is distributed under.
  8. Create and test your API. Your app under gcp_fastapi_poetry.api:app will be hosted on CloudRun when it’s deployed.
  9. When you’re ready to release the first version, run the release GitHub action with the “major” option to deploy v1 of your API! (or minor/patch to deploy v0)
  10. Remove this section from
  11. Happy hacking!

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Install Poetry and poetry install the project

Useful Commands

Note: if Poetry is managing a virtual environment for you, you may need to use poetry run poe instead of poe

  • poe autoformat – Autoformat code
  • poe lint – Linting
  • poe test – Run Tests
  • poe local-server – Run your API locally


Release a new version by manually running the release action on GitHub with a ‘major’, ‘minor’, or ‘patch’ version bump selected. This will create an push a new semver tag of the format v1.2.3, and also update the appropriate major version tag (v1, v2, …).

Updating the major version tags will cause Cloud Build to create or update that version’s deployment automatically and host it at e.g. v1.(your configured domain). You may need to configure your domain’s DNS if you’re creating an endpoint for a new major version and you use an external provider. See the domain mappings page linked here for instructions.


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