Cache module dependencies between container builds

Dockerfile

@@ -34,17 +34,18 @@ ENV CGO_ENABLED=0 \
     GOARM=${TARGETVARIANT} \
     LDFLAGS="-X ${PKG}/pkg/buildinfo.Version=${VERSION} -X ${PKG}/pkg/buildinfo.GitSHA=${GIT_SHA} -X ${PKG}/pkg/buildinfo.GitTreeState=${GIT_TREE_STATE} -X ${PKG}/pkg/buildinfo.ImageRegistry=${REGISTRY}"
 
+RUN mkdir -p /output/usr/bin
 WORKDIR /go/src/github.com/vmware-tanzu/velero
-
+COPY go.mod go.sum /go/src/github.com/vmware-tanzu/velero/
+# --mount=type=cache,target=/go/pkg/mod,id=vbb allows reuse of build cache across builds instead of invalidating whole cache when go.mod changes
+# id is to allow other stages to use the same cache path without conflicting with this stage.
+# velero-builder and restic-builder uses a different go.mod from each other. id helps to avoid sharing cache with velero-builder.
+RUN --mount=type=cache,target=/go/pkg/mod,id=vbb go mod download
 COPY . /go/src/github.com/vmware-tanzu/velero
-
-RUN mkdir -p /output/usr/bin && \
-    export GOARM=$( echo "${GOARM}" | cut -c2-) && \
-    go build -o /output/${BIN} \
-    -ldflags "${LDFLAGS}" ${PKG}/cmd/${BIN} && \
-    go build -o /output/velero-helper \
-    -ldflags "${LDFLAGS}" ${PKG}/cmd/velero-helper && \
-    go clean -modcache -cache
+RUN --mount=type=cache,target=/go/pkg/mod,id=vbb GOARM=$( echo "${GOARM}" | cut -c2-) go build -o /output/${BIN} \
+    -ldflags "${LDFLAGS}" ${PKG}/cmd/${BIN}
+RUN --mount=type=cache,target=/go/pkg/mod,id=vbb GOARM=$( echo "${GOARM}" | cut -c2-) go build -o /output/velero-helper \
+    -ldflags "${LDFLAGS}" ${PKG}/cmd/velero-helper
 
 # Restic binary build section
 FROM --platform=$BUILDPLATFORM golang:1.22-bookworm AS restic-builder
@@ -63,12 +64,30 @@ ENV CGO_ENABLED=0 \
     GOARCH=${TARGETARCH} \
     GOARM=${TARGETVARIANT}
 
-COPY . /go/src/github.com/vmware-tanzu/velero
-
-RUN mkdir -p /output/usr/bin && \
-    export GOARM=$(echo "${GOARM}" | cut -c2-) && \
-    /go/src/github.com/vmware-tanzu/velero/hack/build-restic.sh && \
-    go clean -modcache -cache
+# /output dir needed by last stage to copy even when BIN is not velero
+RUN mkdir -p /output/usr/bin && mkdir -p /build/restic
+WORKDIR /build/restic
+
+# cache go mod download before applying patches
+RUN --mount=type=cache,target=/go/pkg/mod,id=restic if [ "${BIN}" = "velero" ]; then \
+        git clone --single-branch -b v${RESTIC_VERSION} https://github.com/restic/restic.git . && \
+        go mod download; \
+    fi
+
+# invalidate cache if patch changes
+COPY hack/fix_restic_cve.txt /go/src/github.com/vmware-tanzu/velero/hack/
+
+# cache go mod download after applying patches
+RUN --mount=type=cache,target=/go/pkg/mod,id=restic if [ "${BIN}" = "velero" ]; then \
+        git apply /go/src/github.com/vmware-tanzu/velero/hack/fix_restic_cve.txt && \
+        go mod download; \
+    fi
+
+# arch specific build layer
+RUN --mount=type=cache,target=/go/pkg/mod,id=restic if [ "${BIN}" = "velero" ]; then \ 
+        GOARM=$(echo "${GOARM}" | cut -c2-) go run build.go --goos "${GOOS}" --goarch "${GOARCH}" --goarm "${GOARM}" -o /output/usr/bin/restic && \
+        chmod +x /output/usr/bin/restic; \
+    fi
 
 # Velero image packing section
 FROM paketobuildpacks/run-jammy-tiny:latest