Reducing Binary Size

Q: Does LTO help size?

Yes, merges and dead-strips unused functions across crates.

Q: Why is tokio big?

Enable only needed features: rt-multi-thread, macros, not full unless required.

Q: clap size?

Use clap 4 with derive and disable unused string features; consider argh for tiny CLIs.

Q: serde in binary?

Necessary for JSON APIs; avoid deriving on every internal type if not serialized.

Q: strip vs split debuginfo?

strip for minimal artifact; split for crash reporting with external symbols.

Q: WASM binary size?

wasm-pack build --release + wasm-opt; avoid pulling full std when possible.

Q: musl static size?

Larger than dynamic glibc sometimes; trade portability vs MB.

Q: Count monomorphization?

cargo bloat shows instantiations; reduce generic types in hot crate surface.

Q: Docker distroless?

Small runtime image complements stripped Rust binary; still minimize binary itself.

Rust binaries can grow large from monomorphization and debug symbols. Strip symbols, tune opt-level, disable unused features, and use panic = abort for smaller deploy artifacts.

Recipe

[profile.release]
opt-level = "z"
lto = true
panic = "abort"
strip = "symbols"

cargo bloat --release --crates

When to reach for this: CLI distribution, embedded targets, WASM bundles, and container image slimming.

Working Example

[profile.release]
opt-level = "z"
lto = true
codegen-units = 1
panic = "abort"
strip = "symbols"
 
[features]
default = []

cargo build --release
ls -lh target/release/myapp
cargo bloat --release -n 30

What this demonstrates:

opt-level = "z" optimizes for size over speed
Feature-minimal default reduces compiled code
cargo bloat shows largest functions/crates
strip removes symbol tables from shipped binary

Deep Dive

Size Levers

Lever	Effect
Fewer features on deps	Less code linked
`panic = abort`	No unwinding tables
`strip`	Smaller on disk
Dynamic linking (platform)	Rare in Rust servers
`upx` compression	Last resort, AV issues

WASM Size

[profile.release]
opt-level = "s"

Run wasm-opt -Oz after build for WASM targets.

Gotchas

Size opt without perf check - latency regression in API. Fix: benchmark critical paths after size tuning.
Keeping all default features - pulls tokio full when only rt needed. Fix: default-features = false.
Many generic instantiations - duplicate code. Fix: type erasure on cold paths only.
Debug symbols in Docker - huge layers. Fix: strip in final stage or separate debug symbol package.
abort panics in library - consumers cannot catch. Fix: apps choose panic = abort; libs usually unwind.

Alternatives

Alternative	Use When	Don't Use When
`opt-level = "s"`	Balance size/speed	Extreme size need
`split-debuginfo`	Keep symbols off binary	Need single-file debug
Static musl binary	Portable CLI	glibc DNS nuances

FAQs

How big is too big?

Context-dependent: CLI < few MB ideal; server less critical than container count of deps.

Does LTO help size?

Yes, merges and dead-strips unused functions across crates.

Why is tokio big?

Enable only needed features: rt-multi-thread, macros, not full unless required.

clap size?

Use clap 4 with derive and disable unused string features; consider argh for tiny CLIs.

serde in binary?

Necessary for JSON APIs; avoid deriving on every internal type if not serialized.

strip vs split debuginfo?

strip for minimal artifact; split for crash reporting with external symbols.

WASM binary size?

wasm-pack build --release + wasm-opt; avoid pulling full std when possible.

musl static size?

Larger than dynamic glibc sometimes; trade portability vs MB.

Count monomorphization?

cargo bloat shows instantiations; reduce generic types in hot crate surface.

Docker distroless?

Small runtime image complements stripped Rust binary; still minimize binary itself.

The Cargo Book - Official guide and reference for Cargo.
rustc Book - Compiler flags, internals overview, and usage.
Embedded Rust Book - Official guide for bare-metal / embedded development.
Programming Rust: Fast, Safe Systems Development (Amazon) - Blandy, Orendorff, Tindall.
Mastering Rust: From Beginner to Advanced Level (Leanpub) - Leanpub.

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.

Recipe

[profile.release]
opt-level = "z"
lto = true
panic = "abort"
strip = "symbols"

cargo bloat --release --crates

When to reach for this: CLI distribution, embedded targets, WASM bundles, and container image slimming.

Working Example

[profile.release]
opt-level = "z"
lto = true
codegen-units = 1
panic = "abort"
strip = "symbols"
 
[features]
default = []

cargo build --release
ls -lh target/release/myapp
cargo bloat --release -n 30

What this demonstrates:

opt-level = "z" optimizes for size over speed
Feature-minimal default reduces compiled code
cargo bloat shows largest functions/crates
strip removes symbol tables from shipped binary

Deep Dive

Size Levers

Lever	Effect
Fewer features on deps	Less code linked
`panic = abort`	No unwinding tables
`strip`	Smaller on disk
Dynamic linking (platform)	Rare in Rust servers
`upx` compression	Last resort, AV issues

WASM Size

[profile.release]
opt-level = "s"

Run wasm-opt -Oz after build for WASM targets.

Gotchas

Size opt without perf check - latency regression in API. Fix: benchmark critical paths after size tuning.
Keeping all default features - pulls tokio full when only rt needed. Fix: default-features = false.
Many generic instantiations - duplicate code. Fix: type erasure on cold paths only.
Debug symbols in Docker - huge layers. Fix: strip in final stage or separate debug symbol package.
abort panics in library - consumers cannot catch. Fix: apps choose panic = abort; libs usually unwind.

Alternatives

Alternative	Use When	Don't Use When
`opt-level = "s"`	Balance size/speed	Extreme size need
`split-debuginfo`	Keep symbols off binary	Need single-file debug
Static musl binary	Portable CLI	glibc DNS nuances

FAQs

How big is too big?

Context-dependent: CLI < few MB ideal; server less critical than container count of deps.

Does LTO help size?

Yes, merges and dead-strips unused functions across crates.

Why is tokio big?

Enable only needed features: rt-multi-thread, macros, not full unless required.

clap size?

Use clap 4 with derive and disable unused string features; consider argh for tiny CLIs.

serde in binary?

Necessary for JSON APIs; avoid deriving on every internal type if not serialized.

strip vs split debuginfo?

strip for minimal artifact; split for crash reporting with external symbols.

WASM binary size?

wasm-pack build --release + wasm-opt; avoid pulling full std when possible.

musl static size?

Larger than dynamic glibc sometimes; trade portability vs MB.

Count monomorphization?

cargo bloat shows instantiations; reduce generic types in hot crate surface.

Docker distroless?

Small runtime image complements stripped Rust binary; still minimize binary itself.

The Cargo Book - Official guide and reference for Cargo.
rustc Book - Compiler flags, internals overview, and usage.
Embedded Rust Book - Official guide for bare-metal / embedded development.
Programming Rust: Fast, Safe Systems Development (Amazon) - Blandy, Orendorff, Tindall.
Mastering Rust: From Beginner to Advanced Level (Leanpub) - Leanpub.

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.

Reducing Binary Size

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Reducing Binary Size