In large-scale product development in Rust, using modules (mod) to separate functionality makes it difficult to manage the responsibilities of each component. Cargo Workspace allows to manage multiple crates in a single place, making it easier to separate responsibility.

Especially when developing a backend product, each component responsibility may want to use different dependencies. Using Cargo Workspace to separate the crates also separates the Cargo.toml, making it easier to manage dependencies.

I would like to share best practices based on my experience of 3 years of continuous backend development of our own products. Examples of good and bad points are as follows.

• How to consist versions of dependencies in own crates (solved in workspace.dependencies in 1.64.0)
• How to handle common types
• It is easier to mock APIs of external services
• When using Procedural macro, it is necessary to separate the crates, but the crates can be in the same workspace
• It is good to match the prefix or suffix of each crate's name
• To publish to crates.io, cargo-release is useful.
• etc.