cargo-chefwas initially developed for the deployment chapter of Zero to Production In Rust, a hands-on introduction to backend development using the Rust programming language.
Table of Contents
How To Install
You can install
cargo-chef from crates.io with
cargo install cargo-chef --locked
How to use
⚠️cargo-chef is not meant to be run locally
Its primary use-case is to speed up container builds by running BEFORE the actual source code is copied over. Don't run it on existing codebases to avoid having files being overwritten.
cargo-chef exposes two commands:
cargo chef --help
cargo-chef USAGE: cargo chef <SUBCOMMAND> SUBCOMMANDS: cook Re-hydrate the minimum project skeleton identified by `cargo chef prepare` and build it to cache dependencies prepare Analyze the current project to determine the minimum subset of files (Cargo.lock and Cargo.toml manifests) required to build it and cache dependencies
prepare examines your project and builds a recipe that captures the set of information required to build your dependencies.
cargo chef prepare --recipe-path recipe.json
Nothing too mysterious going on here, you can examine the
recipe.json file: it contains the skeleton of your project (e.g. all the
Cargo.toml files with their relative path, the
Cargo.lock file is available) plus a few additional pieces of information.
In particular it makes sure that all libraries and binaries are explicitly declared in their respective
Cargo.toml files even if they can be found at the canonical default location (
src/main.rs for a binary,
src/lib.rs for a library).
recipe.json is the equivalent of the Python
requirements.txt file - it is the only input required for
cargo chef cook, the command that will build out our dependencies:
cargo chef cook --recipe-path recipe.json
If you want to build in
cargo chef cook --release --recipe-path recipe.json
You can also choose to override which Rust toolchain should be used. E.g., to force the
cargo +nightly chef cook --recipe-path recipe.json
cargo-chef is designed to be leveraged in Dockerfiles:
FROM lukemathwalker/cargo-chef:latest-rust-1 AS chef WORKDIR /app FROM chef AS planner COPY . . RUN cargo chef prepare --recipe-path recipe.json FROM chef AS builder COPY --from=planner /app/recipe.json recipe.json # Build dependencies - this is the caching Docker layer! RUN cargo chef cook --release --recipe-path recipe.json # Build application COPY . . RUN cargo build --release --bin app # We do not need the Rust toolchain to run the binary! FROM debian:buster-slim AS runtime WORKDIR /app COPY --from=builder /app/target/release/app /usr/local/bin ENTRYPOINT ["/usr/local/bin/app"]
We are using three stages: the first computes the recipe file, the second caches our dependencies and builds the binary, the third is our runtime environment.
As long as your dependencies do not change the
recipe.json file will stay the same, therefore the outcome of
cargo chef cook --release --recipe-path recipe.json will be cached, massively speeding up your builds (up to 5x measured on some commercial projects).
lukemathwalker/cargo-chef as a pre-built Docker image equipped with both Rust and
The tagging scheme is
<cargo-chef version>-rust-<rust version>.
You can choose to get the latest version of either
rust by using:
cargo-chefwith specific Rust version);
0.1.22-rust-latest(use latest Rust with specific
cargo-chefversion). You can find all the available tags on Dockerhub.
⚠️You must use the same Rust version in all stages
If you use a different Rust version in one of the stages caching will not work as expected.
Without the pre-built image
If you do not want to use the
lukemathwalker/cargo-chef image, you can simply install the CLI within the Dockerfile:
FROM rust:1 AS chef # We only pay the installation cost once, # it will be cached from the second build onwards RUN cargo install cargo-chef WORKDIR app FROM chef AS planner COPY . . RUN cargo chef prepare --recipe-path recipe.json FROM chef AS builder COPY --from=planner /app/recipe.json recipe.json # Build dependencies - this is the caching Docker layer! RUN cargo chef cook --release --recipe-path recipe.json # Build application COPY . . RUN cargo build --release --bin app # We do not need the Rust toolchain to run the binary! FROM debian:buster-slim AS runtime WORKDIR app COPY --from=builder /app/target/release/app /usr/local/bin ENTRYPOINT ["/usr/local/bin/app"]
Running the binary in Alpine
If you want to run your application using the
alpine distribution you need to create a fully static binary.
The recommended approach is to build for the
x86_64-unknown-linux-musl target using
cargo-chef works for
x86_64-unknown-linux-musl, but we are cross-compiling - the target
toolchain must be explicitly specified.
A sample Dockerfile looks like this:
# Using the `rust-musl-builder` as base image, instead of # the official Rust toolchain FROM clux/muslrust:stable AS chef USER root RUN cargo install cargo-chef WORKDIR /app FROM chef AS planner COPY . . RUN cargo chef prepare --recipe-path recipe.json FROM chef AS builder COPY --from=planner /app/recipe.json recipe.json # Notice that we are specifying the --target flag! RUN cargo chef cook --release --target x86_64-unknown-linux-musl --recipe-path recipe.json COPY . . RUN cargo build --release --target x86_64-unknown-linux-musl --bin app FROM alpine AS runtime RUN addgroup -S myuser && adduser -S myuser -G myuser COPY --from=builder /app/target/x86_64-unknown-linux-musl/release/app /usr/local/bin/ USER myuser CMD ["/usr/local/bin/app"]
Benefits vs Limitations
cargo-chef has been tested on a few OpenSource projects and some of commercial projects, but our testing has definitely not exhausted the range of possibilities when it comes to
cargo build customisations and we are sure that there are a few rough edges that will have to be smoothed out - please file issues on GitHub.
A common alternative is to load a minimal
main.rs into a container with
Cargo.lock to build a Docker layer that consists of only your dependencies (more info here). This is fragile compared to
cargo-chef which will instead:
- automatically pick up all crates in a workspace (and new ones as they are added)
- keep working when files or crates are moved around, which would instead require manual edits to the
Dockerfileusing the "manual" approach
- generate fewer intermediate Docker layers (for workspaces)
Limitations and caveats:
cargo buildmust be executed from the same working directory. If you examine the
target/debug/depsfor one of your projects using
catyou will notice that they contain absolute paths referring to the project
targetdirectory. If moved around,
cargowill not leverage them as cached dependencies;
cargo buildwill build local dependencies (outside of the current project) from scratch, even if they are unchanged, due to the reliance of its fingerprinting logic on timestamps (see this long issue on
Licensed under either of Apache License, Version 2.0 or MIT license at your option. Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.