Improve Dockerfile (#207)

.dockerignore

@@ -0,0 +1,9 @@
+**/.dockerignore
+**/.github
+**/.gitignore
+**/.vscode
+**/compose*
+**/Dockerfile*
+LICENSE
+README.md
+todoapp

Dockerfile

@@ -1,12 +1,29 @@
-FROM cgr.dev/chainguard/go:latest as builder
+# syntax=docker/dockerfile:1
 
-WORKDIR /app
-COPY . .
-RUN CGO_ENABLED=0 go build -o todoapp ./cmd/todoapp
+FROM cgr.dev/chainguard/go:latest as build
+
+WORKDIR /src
+
+# Download dependencies as a separate step to take advantage of Docker's caching.
+# Leverage a cache mount to /go/pkg/mod/ to speed up subsequent builds.
+# Leverage bind mounts to go.sum and go.mod to avoid having to copy them into
+# the container.
+RUN --mount=type=cache,target=/go/pkg/mod/ \
+    --mount=type=bind,source=go.sum,target=go.sum \
+    --mount=type=bind,source=go.mod,target=go.mod \
+    go mod download -x
+
+# Build the application.
+# Leverage a cache mount to /go/pkg/mod/ to speed up subsequent builds.
+# Leverage a bind mount to the current directory to avoid having to copy the
+# source code into the container.
+RUN --mount=type=cache,target=/go/pkg/mod/ \
+    --mount=type=bind,target=. \
+    CGO_ENABLED=0 go build -o /bin/server ./cmd/todoapp
 
 FROM cgr.dev/chainguard/static:latest
 
+COPY --from=build /bin/server /bin/
 EXPOSE 8080
-COPY --from=builder /app/todoapp /todoapp
 
-ENTRYPOINT ["/todoapp"]
+ENTRYPOINT [ "/bin/server" ]