flyctl [build] accepts Dockerfile URLs
Introduced 2026-07-27 · score 0.97
HOW TO USE IT
When `[build].dockerfile` is hosted remotely, set it to the Dockerfile URL and deploy from the repository root; flyctl keeps the project root as the default build context. The URL is downloaded when a Dockerfile builder needs it and the same copy is reused throughout the deploy.
[build]
dockerfile = "<Dockerfile URL>"
flyctl deployWHY THIS HELPS
Deploy a repository whose `[build] dockerfile` is hosted remotely while retaining the local build context.
BEFORE THIS CHANGE
Set `[build] dockerfile` to a local path for Dockerfile builds.
REQUIREMENTS AND LIMITATIONS
- Version: v0.4.75
- [build].dockerfile: Accepts a relative Dockerfile path or a URL; defaults to `Dockerfile` in the application root. It does not change the Docker context, which defaults to the project root.
- Prerequisite: Install flyctl and sign in to a Fly account before deploying.
- The URL is fetched only when a Dockerfile builder needs it.
- Downloads have a 30 second timeout and a 10 MiB limit.
- The downloaded file is stored in a private temporary directory that is cleaned up before deploy continues.
- Redirects drop query-bearing Referer headers and refuse HTTPS-to-HTTP downgrades.
- Local Dockerfiles and non-Dockerfile builds are unchanged.
FIRST-PARTY EVIDENCE
- https://github.com/superfly/flyctl/releases/tag/v0.4.75
- https://github.com/superfly/flyctl/pull/5021
- https://github.com/superfly/docs/blob/main/reference/configuration.html.markerb
- https://github.com/superfly/flyctl
Check the installed version and the source before using it. Entry JSON