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Build Optimisations

FluentDo Agent is ~70% smaller than OSS Fluent Bit through strategic optimisations while maintaining security and performance.

Optimisation Techniques

1. Strategic Plugin Selection

17 vendor-specific and specialized plugins are disabled by default to reduce binary size and attack surface. See Security Documentation for the complete list of disabled plugins.

2. Compiler Optimisations

  • Size-optimised compilation (-Os) - Optimises for size over speed
  • Function/data sections (-ffunction-sections -fdata-sections) - Enables granular dead code elimination
  • Dead code elimination - Platform-specific:
  • Linux: -Wl,--gc-sections
  • macOS: -Wl,-dead_strip
  • Interprocedural optimisation (IPO/LTO) - Cross-function optimisation and inlining

3. Build System Configuration

  • Static binary preferred - FLB_SHARED_LIB=OFF eliminates shared library dependencies
  • Disabled development features:
  • Examples (FLB_EXAMPLES=OFF)
  • Stream processor (FLB_STREAM_PROCESSOR=OFF)
  • WASM runtime (FLB_WASM=OFF)
  • Zig integration (FLB_ZIG=OFF)
  • Go plugin support (FLB_PROXY_GO=OFF)
  • Debug chunk tracing (FLB_CHUNK_TRACE=OFF)

4. Docker Optimisations

  • Explicit CMAKE_BUILD_TYPE=Release for proper optimisations
  • Binary stripping post-compilation (strip bin/fluent-bit)
  • Minimal base image dependencies (removed libpq, systemd-libs, shadow-utils)

5. Platform-Specific Fixes

macOS ARM64 LuaJIT Fix

Addresses buildvm crashes on Apple Silicon by isolating LuaJIT compilation from global optimisation flags:

# Save and clear optimisation flags for LuaJIT
set(SAVED_CMAKE_C_FLAGS "${CMAKE_C_FLAGS}")
set(CMAKE_C_FLAGS "")
set(BUILDVM_COMPILER_FLAGS "-O0")
add_subdirectory("lib/luajit-cmake")
# Restore flags after LuaJIT build
set(CMAKE_C_FLAGS "${SAVED_CMAKE_C_FLAGS}")

Size Impact

Metric OSS Fluent Bit FluentDo Agent Reduction
Docker Image Size ~500MB ~150MB ~70%
Binary Size ~50-60MB ~15-20MB ~67%
Memory Usage ~50-70MB RSS ~20-30MB RSS ~57%

Trade-offs

Functionality vs Size

  • Disabled plugins must be explicitly enabled if needed
  • Vendor-specific integrations require recompilation

Performance Considerations

  • -Os may have minor performance impact vs -O2
  • IPO/LTO increases build time but improves runtime efficiency
  • Static linking increases binary size but simplifies deployment

Security Benefits

  • Reduced attack surface from disabled plugins
  • Smaller codebase easier to audit
  • Fewer dependencies reduce supply chain risks

Enabling Disabled Plugins

If you need plugins that are disabled by default, you can:

  1. Request a custom build from FluentDo support with specific plugins enabled
  2. Use OSS Fluent Bit if vendor-specific plugins are required
  3. Build from source with your required configuration