Cache sharing strategy

When implementing caching in build systems, carefully configure cache sharing behavior based on your concurrency requirements. Improper sharing settings can lead to build failures when multiple processes attempt to access the same cache simultaneously.

For Docker BuildKit cache mounts:

• Use sharing=shared (default) for caches with internal locking mechanisms or read-only access patterns
• Use sharing=locked when cache contents cannot handle concurrent writers
• Use sharing=private for isolated per-build caches that don’t benefit from sharing
• Consider using tmpfs mounts to exclude directories containing temporary or easily regenerated data

Example of proper cache configuration:

RUN \
  # Global cache that safely handles concurrent access
  --mount=type=cache,target=/var/lib/apt/lists,type=cache,sharing=shared \
  # Cache that needs exclusive access to prevent corruption
  --mount=type=cache,target="/root/.cache/rustup",id="rustup-toolchain",sharing=locked \
  # Project-specific build cache with isolated ID to prevent unintended sharing
  --mount=type=cache,target="target/",id="cargo-target-${APP_NAME}-${TARGETPLATFORM}",sharing=locked \
  # Exclude temporary directories from caching with tmpfs
  --mount=type=tmpfs,target="${CARGO_HOME}/registry/src" \
  --mount=type=tmpfs,target="${CARGO_HOME}/git/checkouts" \
  cargo build --release

Always consider the concurrency patterns of your build environment. Remember that caches with the same ID are shared across different builds, which can cause unexpected interactions between unrelated projects.