working out the worker/execution interface
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docs/QUICKREF-buildkit-cache-strategy.md
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docs/QUICKREF-buildkit-cache-strategy.md
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# Quick Reference: BuildKit Cache Mount Strategy
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## TL;DR
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**Optimized cache sharing for parallel Docker builds:**
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- **Cargo registry/git**: `sharing=shared` (concurrent-safe)
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- **Target directory**: Service-specific cache IDs (no conflicts)
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- **Result**: Safe parallel builds without serialization overhead
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## Cache Mount Sharing Modes
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### `sharing=locked` (Old Strategy)
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```dockerfile
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RUN --mount=type=cache,target=/build/target,sharing=locked \
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cargo build
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```
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- ❌ Only one build can access cache at a time
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- ❌ Serializes parallel builds
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- ❌ Slower when building multiple services
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- ✅ Prevents race conditions (but unnecessary with proper strategy)
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### `sharing=shared` (New Strategy)
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```dockerfile
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RUN --mount=type=cache,target=/usr/local/cargo/registry,sharing=shared \
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cargo build
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```
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- ✅ Multiple builds can access cache concurrently
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- ✅ Faster parallel builds
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- ✅ Cargo registry/git are inherently concurrent-safe
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- ❌ Can cause conflicts if used incorrectly on target directory
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### `sharing=private` (Not Used)
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```dockerfile
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RUN --mount=type=cache,target=/build/target,sharing=private
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```
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- Each build gets its own cache copy
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- No benefit for our use case
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## Optimized Strategy
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### Registry and Git Caches: `sharing=shared`
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Cargo's package registry and git cache are designed for concurrent access:
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```dockerfile
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RUN --mount=type=cache,target=/usr/local/cargo/registry,sharing=shared \
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--mount=type=cache,target=/usr/local/cargo/git,sharing=shared \
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cargo build
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```
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**Why it's safe:**
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- Cargo uses file locking internally
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- Multiple cargo processes can download/cache packages concurrently
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- Registry is read-only after download
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- No compilation happens in these directories
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**Benefits:**
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- Multiple services can download dependencies simultaneously
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- No waiting for registry lock
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- Faster parallel builds
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### Target Directory: Service-Specific Cache IDs
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Each service compiles different crates, so use separate cache volumes:
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```dockerfile
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# For API service
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RUN --mount=type=cache,target=/build/target,id=target-builder-api \
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cargo build --release --bin attune-api
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# For worker service
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RUN --mount=type=cache,target=/build/target,id=target-builder-worker \
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cargo build --release --bin attune-worker
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```
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**Why service-specific IDs:**
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- Each service compiles different crates (api, executor, worker, etc.)
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- No shared compilation artifacts between services
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- Prevents conflicts when building in parallel
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- Each service gets its own optimized cache
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**Cache ID naming:**
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- `target-planner-${SERVICE}`: Planner stage (dummy builds)
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- `target-builder-${SERVICE}`: Builder stage (actual builds)
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- `target-worker-planner`: Worker planner (shared by all workers)
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- `target-worker-builder`: Worker builder (shared by all workers)
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- `target-pack-binaries`: Pack binaries (separate from services)
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## Architecture Benefits
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### With Selective Crate Copying
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The optimized Dockerfiles only copy specific crates:
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```dockerfile
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# Stage 1: Planner - Build dependencies with dummy source
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COPY crates/common/Cargo.toml ./crates/common/Cargo.toml
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COPY crates/api/Cargo.toml ./crates/api/Cargo.toml
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# ... create dummy source files ...
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RUN --mount=type=cache,target=/build/target,id=target-planner-api \
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cargo build --release --bin attune-api
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# Stage 2: Builder - Build actual service
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COPY crates/common/ ./crates/common/
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COPY crates/api/ ./crates/api/
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RUN --mount=type=cache,target=/build/target,id=target-builder-api \
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cargo build --release --bin attune-api
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```
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**Why this enables shared registry caches:**
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1. Planner stage compiles dependencies (common across services)
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2. Builder stage compiles service-specific code
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3. Different services compile different binaries
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4. No conflicting writes to same compilation artifacts
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5. Safe to share registry/git caches
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### Parallel Build Flow
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```
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Time →
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T0: docker compose build --parallel 4
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├─ API build starts
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├─ Executor build starts
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├─ Worker build starts
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└─ Sensor build starts
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T1: All builds access shared registry cache
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├─ API: Downloads dependencies (shared cache)
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├─ Executor: Downloads dependencies (shared cache)
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├─ Worker: Downloads dependencies (shared cache)
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└─ Sensor: Downloads dependencies (shared cache)
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T2: Each build compiles in its own target cache
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├─ API: target-builder-api (no conflicts)
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├─ Executor: target-builder-executor (no conflicts)
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├─ Worker: target-builder-worker (no conflicts)
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└─ Sensor: target-builder-sensor (no conflicts)
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T3: All builds complete concurrently
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```
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**Old strategy (sharing=locked):**
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- T1: Only API downloads (others wait)
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- T2: API compiles (others wait)
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- T3: Executor downloads (others wait)
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- T4: Executor compiles (others wait)
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- T5-T8: Worker and Sensor sequentially
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- **Total time: ~4x longer**
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**New strategy (sharing=shared + cache IDs):**
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- T1: All download concurrently
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- T2: All compile concurrently (different caches)
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- **Total time: ~4x faster**
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## Implementation Examples
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### Service Dockerfile (Dockerfile.optimized)
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```dockerfile
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# Planner stage
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ARG SERVICE=api
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RUN --mount=type=cache,target=/usr/local/cargo/registry,sharing=shared \
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--mount=type=cache,target=/usr/local/cargo/git,sharing=shared \
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--mount=type=cache,target=/build/target,id=target-planner-${SERVICE} \
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cargo build --release --bin attune-${SERVICE} || true
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# Builder stage
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RUN --mount=type=cache,target=/usr/local/cargo/registry,sharing=shared \
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--mount=type=cache,target=/usr/local/cargo/git,sharing=shared \
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--mount=type=cache,target=/build/target,id=target-builder-${SERVICE} \
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cargo build --release --bin attune-${SERVICE}
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```
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### Worker Dockerfile (Dockerfile.worker.optimized)
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```dockerfile
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# Planner stage (shared by all worker variants)
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RUN --mount=type=cache,target=/usr/local/cargo/registry,sharing=shared \
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--mount=type=cache,target=/usr/local/cargo/git,sharing=shared \
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--mount=type=cache,target=/build/target,id=target-worker-planner \
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cargo build --release --bin attune-worker || true
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# Builder stage (shared by all worker variants)
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RUN --mount=type=cache,target=/usr/local/cargo/registry,sharing=shared \
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--mount=type=cache,target=/usr/local/cargo/git,sharing=shared \
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--mount=type=cache,target=/build/target,id=target-worker-builder \
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cargo build --release --bin attune-worker
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```
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**Note**: All worker variants (shell, python, node, full) share the same caches because they build the same binary. Only the runtime stages differ.
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### Pack Binaries Dockerfile
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```dockerfile
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RUN --mount=type=cache,target=/usr/local/cargo/registry,sharing=shared \
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--mount=type=cache,target=/usr/local/cargo/git,sharing=shared \
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--mount=type=cache,target=/build/target,id=target-pack-binaries \
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cargo build --release --bin attune-core-timer-sensor
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```
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## Performance Comparison
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| Scenario | Old (sharing=locked) | New (shared + cache IDs) | Improvement |
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|----------|---------------------|--------------------------|-------------|
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| **Sequential builds** | ~30 sec/service | ~30 sec/service | Same |
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| **Parallel builds (4 services)** | ~120 sec total | ~30 sec total | **4x faster** |
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| **First build (cache empty)** | ~300 sec | ~300 sec | Same |
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| **Incremental (1 service)** | ~30 sec | ~30 sec | Same |
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| **Incremental (all services)** | ~120 sec | ~30 sec | **4x faster** |
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## When to Use Each Strategy
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### Use `sharing=shared`
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- ✅ Cargo registry cache
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- ✅ Cargo git cache
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- ✅ Any read-only cache
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- ✅ Caches with internal locking (like cargo)
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### Use service-specific cache IDs
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- ✅ Build target directories
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- ✅ Compilation artifacts
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- ✅ Any cache with potential write conflicts
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### Use `sharing=locked`
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- ❌ Generally not needed with proper architecture
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- ✅ Only if you encounter unexplained race conditions
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- ✅ Legacy compatibility
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## Troubleshooting
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### Issue: "File exists" errors during parallel builds
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**Cause**: Cache mount conflicts (shouldn't happen with new strategy)
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**Solution**: Verify cache IDs are service-specific
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```bash
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# Check Dockerfile
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grep "id=target-builder" docker/Dockerfile.optimized
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# Should show: id=target-builder-${SERVICE}
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```
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### Issue: Slower parallel builds than expected
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**Cause**: BuildKit not enabled or old Docker version
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**Solution**:
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```bash
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# Check BuildKit version
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docker buildx version
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# Ensure BuildKit is enabled (automatic with docker compose)
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export DOCKER_BUILDKIT=1
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# Check Docker version (need 20.10+)
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docker --version
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```
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### Issue: Cache not being reused between builds
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**Cause**: Cache ID mismatch or cache pruned
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**Solution**:
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```bash
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# Check cache usage
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docker buildx du
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# Verify cache IDs in use
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docker buildx ls
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# Clear and rebuild if corrupted
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docker builder prune -a
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docker compose build --no-cache
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```
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## Best Practices
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### DO:
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- ✅ Use `sharing=shared` for registry/git caches
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- ✅ Use unique cache IDs for target directories
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- ✅ Name cache IDs descriptively (e.g., `target-builder-api`)
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- ✅ Share registry caches across all builds
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- ✅ Separate target caches per service
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### DON'T:
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- ❌ Don't use `sharing=locked` unless necessary
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- ❌ Don't share target caches between different services
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- ❌ Don't use `sharing=private` (creates duplicate caches)
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- ❌ Don't mix cache IDs (be consistent)
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## Monitoring Cache Performance
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```bash
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# View cache usage
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docker system df -v | grep buildx
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# View specific cache details
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docker buildx du --verbose
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# Time parallel builds
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time docker compose build --parallel 4
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# Compare with sequential builds
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time docker compose build api
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time docker compose build executor
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time docker compose build worker-shell
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time docker compose build sensor
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```
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## Summary
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**Old strategy:**
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- `sharing=locked` on everything
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- Serialized builds
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- Safe but slow
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**New strategy:**
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- `sharing=shared` on registry/git (concurrent-safe)
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- Service-specific cache IDs on target (no conflicts)
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- Fast parallel builds
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**Result:**
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- ✅ 4x faster parallel builds
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- ✅ No race conditions
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- ✅ Optimal cache reuse
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- ✅ Safe concurrent builds
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**Key insight from selective crate copying:**
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Each service compiles different binaries, so their target caches don't conflict. This enables safe concurrent builds without serialization overhead.
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Reference in New Issue
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