refactor: build binaries on the host to improve build/module cache reuse (#68)

Author: alecthomas

.dockerignore

@@ -1,6 +1,4 @@
-# Build artifacts
-dist/
-**/dist/
+# Build artifacts (dist/ is allowed for pre-built binaries)
 
 # Git
 .git/

Justfile

@@ -39,7 +39,8 @@ fmt:
 build GOOS=(GOOS) GOARCH=(GOARCH):
     #!/usr/bin/env bash
     mkdir -p {{ RELEASE }}
-    go build -trimpath -o {{ RELEASE }}/cachewd-{{ GOOS }}-{{ GOARCH }} \
+    CGO_ENABLED=0 GOOS={{ GOOS }} GOARCH={{ GOARCH }} \
+        go build -trimpath -o {{ RELEASE }}/cachewd-{{ GOOS }}-{{ GOARCH }} \
         -ldflags "-s -w -X main.version={{ VERSION }} -X main.gitCommit={{ GIT_COMMIT }}" \
         ./cmd/cachewd
     test "{{ GOOS }}-{{ GOARCH }}" = "$(go env GOOS)-$(go env GOARCH)" && (cd {{ RELEASE }} && ln -sf cachewd-{{ GOOS }}-{{ GOARCH }} cachewd)

docker/Dockerfile

@@ -1,51 +1,27 @@
-# Build stage
-FROM golang:1.25.5-alpine AS builder
+# Runtime image - binaries are pre-built on the host
+FROM alpine:3.21
 
-ARG VERSION=dev
-ARG GIT_COMMIT=unknown
-ARG TARGETOS
 ARG TARGETARCH
 
-WORKDIR /build
-
-# Install build dependencies
-RUN apk add --no-cache git ca-certificates tzdata
-
-# Copy go mod files first for better caching
-COPY go.mod go.sum ./
-RUN go mod download
-
-# Copy source code
-COPY . .
-
-# Build the binary
-RUN CGO_ENABLED=0 GOOS=${TARGETOS} GOARCH=${TARGETARCH} \
-    go build -trimpath -o cachewd \
-    -ldflags "-s -w -X main.version=${VERSION} -X main.gitCommit=${GIT_COMMIT}" \
-    ./cmd/cachewd
-
-# Runtime stage
-FROM alpine:3.21
-
 SHELL ["/bin/sh", "-o", "pipefail", "-c"]
 
 # Install runtime dependencies for git operations and TLS
 RUN apk add --no-cache ca-certificates git tzdata && \
-    addgroup -g 1000 cachew && \
-    adduser -D -u 1000 -G cachew cachew
+  addgroup -g 1000 cachew && \
+  adduser -D -u 1000 -G cachew cachew
 
 # Set working directory (config uses relative paths like ./state/cache)
 WORKDIR /app
 
-# Copy binary from builder
-COPY --from=builder /build/cachewd /usr/local/bin/cachewd
+# Copy pre-built binary from host (built by Justfile)
+COPY dist/cachewd-linux-${TARGETARCH} /usr/local/bin/cachewd
 
 # Copy default configuration file
 COPY cachew.hcl /app/cachew.hcl
 
 # Create state directory with proper permissions
 RUN mkdir -p /app/state/cache && \
-    chown -R cachew:cachew /app
+  chown -R cachew:cachew /app
 
 # Switch to non-root user
 USER cachew

docker/Justfile

@@ -7,9 +7,12 @@ TAG := `git rev-parse --short HEAD 2>/dev/null || echo "dev"`
 VERSION := `git describe --tags --always --dirty 2>/dev/null || echo "dev"`
 GIT_COMMIT := `git rev-parse HEAD 2>/dev/null || echo "unknown"`
 DOCKERFILE := ROOT + "/docker/Dockerfile"
+RELEASE := ROOT + "/dist"
 
 # Build Docker image for local development
 build:
+    @echo "Building Linux binary for current architecture..."
+    @just -f {{ ROOT }}/Justfile build linux
     @echo "Building Docker image..."
     @docker build -f {{ DOCKERFILE }} \
         --build-arg VERSION={{ VERSION }} \
@@ -20,6 +23,9 @@ build:
 
 # Build multi-arch Docker image (builds for amd64 + arm64, stays in cache)
 build-multi:
+    @echo "Building Linux binaries for amd64 and arm64..."
+    @just -f {{ ROOT }}/Justfile build linux amd64
+    @just -f {{ ROOT }}/Justfile build linux arm64
     @docker buildx create --use --driver docker-container --driver-opt image=moby/buildkit:v0.17.3 --name multi-arch-cachew 2>/dev/null || docker buildx use multi-arch-cachew
     @echo "Building multi-arch image..."
     @docker buildx build \