Pass BUILD_TIME as build arg to Dockerfiles for better caching

Changed Dockerfiles to accept BUILD_TIME as a build argument instead of
generating it inside the Docker build. This allows better layer caching
since the timestamp no longer invalidates the build cache. Updated
build-all-images.sh and collector-build.sh to pass the timestamp.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Dockerfile

@@ -24,8 +24,8 @@ COPY . .
 RUN go mod tidy -e
 
 # Build the binary with proper tags for Alpine and inject build timestamp
-RUN BUILD_TIME=$(date -u +"%Y-%m-%dT%H:%M:%SZ") && \
-    CGO_ENABLED=1 GOOS=linux go build \
+ARG BUILD_TIME
+RUN CGO_ENABLED=1 GOOS=linux go build \
     -buildvcs=false \
     -tags "sqlite_omit_load_extension" \
     -ldflags "-X github.com/selfhosters-cc/container-census/internal/version.BuildTime=${BUILD_TIME}" \

Dockerfile.agent

@@ -24,8 +24,8 @@ COPY . .
 RUN go mod tidy -e
 
 # Build the agent binary with build time
-RUN BUILD_TIME=$(date -u +"%Y-%m-%dT%H:%M:%SZ") && \
-    CGO_ENABLED=0 GOOS=linux go build -buildvcs=false \
+ARG BUILD_TIME
+RUN CGO_ENABLED=0 GOOS=linux go build -buildvcs=false \
     -ldflags="-w -s -X github.com/selfhosters-cc/container-census/internal/version.BuildTime=${BUILD_TIME}" \
     -o census-agent ./cmd/agent
 

Dockerfile.telemetry-collector

@@ -22,8 +22,11 @@ COPY . .
 # Tidy if needed (rarely changes cache)
 RUN go mod tidy -e
 
-# Build the telemetry collector binary
-RUN CGO_ENABLED=0 GOOS=linux go build -buildvcs=false -ldflags="-w -s" -o telemetry-collector ./cmd/telemetry-collector
+# Build the telemetry collector binary with build time injection
+ARG BUILD_TIME
+RUN CGO_ENABLED=0 GOOS=linux go build -buildvcs=false \
+    -ldflags="-w -s -X github.com/selfhosters-cc/container-census/internal/version.BuildTime=${BUILD_TIME}" \
+    -o telemetry-collector ./cmd/telemetry-collector
 
 # Stage 2: Create minimal runtime image
 FROM alpine:3.21

scripts/build-all-images.sh

@@ -131,6 +131,10 @@ build_image() {
         build_args="--build-arg DOCKER_GID=999"
     fi
 
+    # Add BUILD_TIME for all images
+    local build_time=$(date -u +"%Y-%m-%dT%H:%M:%SZ")
+    build_args="$build_args --build-arg BUILD_TIME=$build_time"
+
     # Determine if this is a multi-platform build
     local platform_count=$(echo "$platforms" | tr ',' '\n' | wc -l)
     local load_flag=""
@@ -194,6 +198,10 @@ build_and_push() {
             build_args="--build-arg DOCKER_GID=999"
         fi
 
+        # Add BUILD_TIME for all images
+        local build_time=$(date -u +"%Y-%m-%dT%H:%M:%SZ")
+        build_args="$build_args --build-arg BUILD_TIME=$build_time"
+
         docker buildx build \
             --platform "$platforms" \
             $build_args \

scripts/collector-build.sh

@@ -6,7 +6,14 @@ set -e
 
 cd "$(dirname "$0")/.."
 
+# Get build timestamp in RFC3339 format
+BUILD_TIME=$(date -u +"%Y-%m-%dT%H:%M:%SZ")
+
 echo "Building telemetry collector..."
-CGO_ENABLED=1 go build -o /tmp/telemetry-collector ./cmd/telemetry-collector
+CGO_ENABLED=1 go build \
+  -ldflags "-X github.com/selfhosters-cc/container-census/internal/version.BuildTime=${BUILD_TIME}" \
+  -o /tmp/telemetry-collector \
+  ./cmd/telemetry-collector
 
 echo "Built: /tmp/telemetry-collector"
+ls -lh /tmp/telemetry-collector