Optimize Docker build with bind mounts (#208)

* Optimize Docker build with bind mounts

This commit further optimize the Docker builds on top of PR #92 with:

1. Add .dockerignore file to exclude non-source code files [1].

2. Use Alpine image variant for build stage to reduce download size.
   golang:1.23.7-alpine is 200 MB smaller than golang:1.23.7 [2][3].

3. Replace COPY instruction with RUN --mount=type=bind. Bind mounts do
   not add unnecessary layers to the cache [4][5].

[1]: https://docs.docker.com/build-cloud/optimization/#dockerignore-files
[2]: https://hub.docker.com/layers/library/golang/1.23.7-alpine/images/sha256-333d4ba78773b3a3ae9cf2cff8962df56effc5c9481faa355f211abf2baf175c
[3]: https://hub.docker.com/layers/library/golang/1.23.7/images/sha256-2087a99c3235972660b3d35c1564d9d1a3f639dcace9c790acbabc7e938d1570
[4]: https://docs.docker.com/build/building/best-practices/#add-or-copy
[5]: https://docs.docker.com/build/cache/optimize/#use-bind-mounts

Signed-off-by: Eng Zer Jun <[email protected]>

* Remove `go mod download` step

`go build` will automatically download module dependencies. In many
cases, that is a much smaller set of modules than what is downloaded by
`go mod download`.

Size of GOMODCACHE with `go mod download:

	$ go clean -i -r -cache -modcache
	$ go mod download
	$ du -sh ~/go/pkg/mod
	186M	/home/jun/go/pkg/mod

Size of GOMODCACHE with `go build`:

	$ go clean -i -r -cache -modcache
	$ CGO_ENABLED=0 go build -ldflags="-s -w" cmd/github-mcp-server/main.go
	go: downloading github.com/spf13/viper v1.20.1
	go: downloading github.com/mark3labs/mcp-go v0.18.0
	go: downloading github.com/google/go-github/v69 v69.2.0
	go: downloading github.com/sirupsen/logrus v1.9.3
	go: downloading github.com/spf13/cobra v1.9.1
	go: downloading golang.org/x/sys v0.31.0
	go: downloading github.com/spf13/afero v1.14.0
	go: downloading github.com/fsnotify/fsnotify v1.8.0
	go: downloading github.com/spf13/cast v1.7.1
	go: downloading github.com/go-viper/mapstructure/v2 v2.2.1
	go: downloading github.com/subosito/gotenv v1.6.0
	go: downloading gopkg.in/yaml.v3 v3.0.1
	go: downloading github.com/spf13/pflag v1.0.6
	go: downloading github.com/pelletier/go-toml/v2 v2.2.3
	go: downloading github.com/sagikazarmark/locafero v0.9.0
	go: downloading golang.org/x/text v0.23.0
	go: downloading github.com/google/uuid v1.6.0
	go: downloading github.com/yosida95/uritemplate/v3 v3.0.2
	go: downloading github.com/sourcegraph/conc v0.3.0
	go: downloading github.com/google/go-querystring v1.1.0
	$ du -sh ~/go/pkg/mod
	80M	/home/jun/go/pkg/mod

Reference: https://stackoverflow.com/a/68172023/7902371
Signed-off-by: Eng Zer Jun <[email protected]>

Author: Juneezee

.dockerignore

@@ -0,0 +1,11 @@
+.github
+.vscode
+script
+third-party
+.dockerignore
+.gitignore
+**/*.yml
+**/*.yaml
+**/*.md
+**/*_test.go
+LICENSE

Dockerfile

@@ -1,27 +1,26 @@
+FROM golang:1.24.2-alpine AS build
 ARG VERSION="dev"
 
-FROM golang:1.24.2 AS build
-# allow this step access to build arg
-ARG VERSION
 # Set the working directory
 WORKDIR /build
 
-RUN go env -w GOMODCACHE=/root/.cache/go-build
+# Install git
+RUN --mount=type=cache,target=/var/cache/apk \
+    apk add git
 
-# Install dependencies
-COPY go.mod go.sum ./
-RUN --mount=type=cache,target=/root/.cache/go-build go mod download
-
-COPY . ./
 # Build the server
-RUN --mount=type=cache,target=/root/.cache/go-build CGO_ENABLED=0 go build -ldflags="-s -w -X main.version=${VERSION} -X main.commit=$(git rev-parse HEAD) -X main.date=$(date -u +%Y-%m-%dT%H:%M:%SZ)" \
-    -o github-mcp-server cmd/github-mcp-server/main.go
+# go build automatically download required module dependencies to /go/pkg/mod
+RUN --mount=type=cache,target=/go/pkg/mod \
+    --mount=type=cache,target=/root/.cache/go-build \
+    --mount=type=bind,target=. \
+    CGO_ENABLED=0 go build -ldflags="-s -w -X main.version=${VERSION} -X main.commit=$(git rev-parse HEAD) -X main.date=$(date -u +%Y-%m-%dT%H:%M:%SZ)" \
+    -o /bin/github-mcp-server cmd/github-mcp-server/main.go
 
 # Make a stage to run the app
 FROM gcr.io/distroless/base-debian12
 # Set the working directory
 WORKDIR /server
 # Copy the binary from the build stage
-COPY --from=build /build/github-mcp-server .
+COPY --from=build /bin/github-mcp-server .
 # Command to run the server
 CMD ["./github-mcp-server", "stdio"]