[Rust][FFI] Build FFI library for Linux musl targets

Add x86_64-unknown-linux-musl and aarch64-unknown-linux-musl matrix rows
to release-ffi.yml, cross-compiled with cargo-zigbuild on the existing
linux-ubuntu-latest runners. Uses RUSTFLAGS=-C target-feature=-crt-static
so the libs link musl dynamically, correct for Alpine hosts. Document the
musl cross-compile in the FFI README. Mirrors the JNI musl support from #347.

Fixes #411

Signed-off-by: Zlata Stefanovic <zlata.stefanovic@databricks.com>

Author: zlata-stefanovic-db

.github/workflows/release-ffi.yml

@@ -22,6 +22,20 @@ jobs:
             dynamic_lib: libzerobus_ffi.so
             artifact_dir: linux-aarch64
             cross: true
+          - runner: { group: databricks-protected-runner-group, labels: linux-ubuntu-latest }
+            target: x86_64-unknown-linux-musl
+            static_lib: libzerobus_ffi.a
+            dynamic_lib: libzerobus_ffi.so
+            artifact_dir: linux-musl-x86_64
+            cross: false
+            zigbuild: true
+          - runner: { group: databricks-protected-runner-group, labels: linux-ubuntu-latest }
+            target: aarch64-unknown-linux-musl
+            static_lib: libzerobus_ffi.a
+            dynamic_lib: libzerobus_ffi.so
+            artifact_dir: linux-musl-aarch64
+            cross: false
+            zigbuild: true
           - runner: { group: databricks-protected-runner-group, labels: windows-server-latest }
             target: x86_64-pc-windows-msvc
             static_lib: zerobus_ffi.lib
@@ -69,9 +83,26 @@ jobs:
         with:
           targets: ${{ matrix.target }}
 
+      - name: Install Zig (musl cross-builds)
+        if: matrix.zigbuild
+        uses: mlugg/setup-zig@a67e68dc5c8281d9608136d3d7ca1b282213e4ac # v2.0.1
+        with:
+          version: 0.13.0
+
+      - name: Install cargo-zigbuild (musl cross-builds)
+        if: matrix.zigbuild
+        run: cargo install cargo-zigbuild --locked --version 0.19.8
+
       - name: Build FFI library
+        if: '!matrix.zigbuild'
         run: cargo build --release -p zerobus-ffi --target ${{ matrix.target }}
 
+      - name: Build FFI library (zigbuild)
+        if: matrix.zigbuild
+        env:
+          RUSTFLAGS: -C target-feature=-crt-static
+        run: cargo zigbuild --release -p zerobus-ffi --target ${{ matrix.target }}
+
       - name: Prepare artifacts
         shell: bash
         run: |

rust/ffi/NEXT_CHANGELOG.md

@@ -6,6 +6,8 @@
 
 ### New Features and Improvements
 
+- Build the FFI library for Linux musl targets (`x86_64-unknown-linux-musl`, `aarch64-unknown-linux-musl`), enabling C/C++ and Go-on-Alpine consumers to link `libzerobus_ffi.a` / `libzerobus_ffi.so` on musl-based (Alpine) containers. Artifacts ship in the `linux-musl-x86_64` / `linux-musl-aarch64` directories. Mirrors the JNI musl support added in #347.
+
 ### Bug Fixes
 
 ### Documentation

rust/ffi/README.md

@@ -22,6 +22,16 @@ cargo build -p zerobus-ffi --release
 rustup target add aarch64-unknown-linux-gnu
 cargo build -p zerobus-ffi --release --target aarch64-unknown-linux-gnu
 
+# Linux musl (Alpine), x86_64 and ARM64 — cross-compiled with cargo-zigbuild.
+# Built with -C target-feature=-crt-static so the libs link musl dynamically,
+# which is correct for dynamically-linked Alpine hosts.
+cargo install cargo-zigbuild
+rustup target add x86_64-unknown-linux-musl aarch64-unknown-linux-musl
+RUSTFLAGS="-C target-feature=-crt-static" \
+  cargo zigbuild -p zerobus-ffi --release --target x86_64-unknown-linux-musl
+RUSTFLAGS="-C target-feature=-crt-static" \
+  cargo zigbuild -p zerobus-ffi --release --target aarch64-unknown-linux-musl
+
 # macOS ARM64 (Apple Silicon)
 rustup target add aarch64-apple-darwin
 cargo build -p zerobus-ffi --release --target aarch64-apple-darwin