You can install cargo-chef
from crates.io with
cargo install cargo-chef
cargo-chef
exposes two commands: prepare
and cook
:
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).
The 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 --release
mode:
cargo chef cook --release --recipe-path recipe.json
You can leverage it in a Dockerfile:
FROM rust as planner
WORKDIR app
# We only pay the installation cost once,
# it will be cached from the second build onwards
RUN cargo install cargo-chef
COPY Cargo.toml Cargo.lock /app/
RUN cargo chef prepare --recipe-path recipe.json
FROM rust as cacher
WORKDIR app
RUN cargo install cargo-chef
COPY --from=planner /app/recipe.json recipe.json
RUN cargo chef cook --release --recipe-path recipe.json
FROM rust as builder
WORKDIR app
COPY . .
# Copy over the cached dependencies
COPY --from=cacher /app/target target
COPY --from=cacher /usr/local/cargo /usr/local/cargo
RUN cargo build --release --bin app
FROM rust as runtime
WORKDIR app
COPY --from=builder /app/target/release/app /usr/local/bin
ENTRYPOINT ["./usr/local/bin/app"]
We are using four stages: the first computes the recipe file, the second caches our dependencies, the third builds the binary and the fourth 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 cargo chef cook --release --recipe-path recipe.json
will be cached, massively speeding up your builds (up to 5x measured on some commercial projects).
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.toml
and 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
Dockerfile
using the "manual" approach - generate fewer intermediate Docker layers (for workspaces)
cargo cook
andcargo build
must be executed from the same working directory. If you examine the*.d
files undertarget/debug/deps
for one of your projects usingcat
you will notice that they contain absolute paths referring to the projecttarget
directory. If moved around,cargo
will not leverage them as cached dependencies;cargo build
will 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 oncargo
's repository);
cargo-chef
has not yet been tested extensively with projects leveraging build files.
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.