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How Brimble builds and runs Rust services, and how to set install, build, and start commands so your app actually starts. Detected via Cargo.toml at the project root (or root directory you set). Service type: Web service (or Worker if you choose that). Leave Install and Build empty. Brimble’s builder (Railpack) detects Rust and runs the right steps for you. What the builder does when install/build are empty:
  1. Installs the Rust toolchain.
  2. Compiles with cargo build --release (for workspaces: cargo build --release --package <pkg>).
  3. Copies the binary from Cargo’s output into bin/ (or your Output directory if set).
  4. Starts with ./bin/<app-name> (or ./<output-directory>/<app-name> if you set one).
<app-name> is the package name from Cargo.toml (e.g. ringroad → ./bin/ringroad).

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Output directory

Cargo still builds into target/release/ first. Output directory is where Brimble places the runnable binary in the final image — not a replacement for Cargo’s build cache path.

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Why not target/release?

cargo build --release writes the binary to target/release/<app-name>. That is Cargo’s normal output directory. The running image does not keep target/. Build caches use it; the final container does not ship it. So a start command like:
will fail with No such file or directory even when the build succeeded. The binary that is in the image lives at:

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Custom build command

If you need a custom Build (flags, features, workspace package), either:
  1. Set Output directory (e.g. bin) and a Start like ./bin/<app-name> — Brimble copies target/release/<app-name> into that directory for you, or
  2. Copy yourself in the build command:
Workspace package example:
Then set Start to ./bin/<app-name> (or match your output directory). A bare cargo build --release with no output directory and no cp leaves no runnable path in the image. The build can succeed and the container still cannot start.

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Install command

Optional. You can set cargo fetch if you want; it is not required when Build is empty.

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Listen on all interfaces

Your process must listen on 0.0.0.0 and the PORT env var Brimble injects (or the port you configure). Binding only to 127.0.0.1 will fail health checks. See Application failed to respond.

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Checklist

  • Prefer empty Build unless you have a reason to override.
  • Start is ./bin/<app-name>, not ./target/release/....
  • If Build is custom, it ends with a copy into bin/.
  • App binds to 0.0.0.0 and $PORT.
Last modified on July 14, 2026