feat: simple example of Dockerfile w/ multi-stage build

Author: KEINOS

Diff for: .github/workflows/docker.yaml

@@ -0,0 +1,22 @@
+name: dockerfile
+
+on:
+  workflow_dispatch:
+  push:
+    tags:
+      - 'v*'
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  dockerfile:
+    name: Run Dockerfiles in examples
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Run example - simple
+        run: |
+          cd ./_example/simple
+          docker build -t simple .
+          docker run simple | grep 99\ こんにちわ世界099

Diff for: _example/simple/Dockerfile

@@ -0,0 +1,45 @@
+# =============================================================================
+#  Multi-stage Dockerfile Example
+# =============================================================================
+#  This is a simple Dockerfile that will build an image of scratch-base image.
+#  Usage:
+#    docker build -t simple:local . && docker run --rm simple:local
+# =============================================================================
+
+# -----------------------------------------------------------------------------
+#  Build Stage
+# -----------------------------------------------------------------------------
+FROM golang:alpine AS build
+
+# Important:
+#   Because this is a CGO enabled package, you are required to set it as 1.
+ENV CGO_ENABLED=1
+
+RUN apk add --no-cache \
+    # Important: required for go-sqlite3
+    gcc \
+    # Required for Alpine
+    musl-dev
+
+WORKDIR /workspace
+
+COPY . /workspace/
+
+RUN \
+    go mod init github.com/mattn/sample && \
+    go mod tidy && \
+    go install -ldflags="-s -w -extldflags \"-static\"" ./simple.go
+
+RUN \
+    # Smoke test
+    set -o pipefail; \
+    /go/bin/simple | grep 99\ こんにちわ世界099
+
+# -----------------------------------------------------------------------------
+#  Main Stage
+# -----------------------------------------------------------------------------
+FROM scratch
+
+COPY --from=build /go/bin/simple /usr/local/bin/simple
+
+ENTRYPOINT [ "/usr/local/bin/simple" ]