build: use scratch base image and add Docker CI workflow

Switch Dockerfile from alpine to scratch with static Go binary.
Add GitHub Actions workflow to build and push to Docker Hub.

Author: outofcoffee

.github/workflows/docker.yaml

@@ -0,0 +1,37 @@
+name: Docker
+
+on:
+  push:
+    branches:
+      - develop
+    tags:
+      - 'v*'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_TOKEN }}
+
+      - name: Set Docker tag
+        id: tag
+        run: |
+          if [[ "${GITHUB_REF}" == refs/tags/v* ]]; then
+            echo "tag=${GITHUB_REF_NAME#v}" >> "$GITHUB_OUTPUT"
+          else
+            echo "tag=beta" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          tags: impostermocks/cli:${{ steps.tag.outputs.tag }}

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.23-alpine AS builder
+FROM golang:1.25-alpine AS builder
 
 WORKDIR /app
 
@@ -9,23 +9,25 @@ RUN go mod download
 # Copy source code
 COPY . .
 
-# Build the binary
-RUN go build -tags lambda.norpc -o imposter-cli
+# Build a statically linked binary
+RUN CGO_ENABLED=0 go build -tags lambda.norpc -ldflags="-s -w" -o imposter-cli
 
-# Final stage
-FROM alpine:latest
-
-RUN apk --no-cache add ca-certificates curl openjdk17-jre docker-cli
+# Create an empty directory to use in the scratch stage
+RUN mkdir /empty
 
-WORKDIR /app
+# Final stage
+FROM scratch
 
-# Copy the binary from builder stage
+COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
 COPY --from=builder /app/imposter-cli /usr/local/bin/imposter
+COPY --from=builder /empty /mocks
+COPY --from=builder /empty /tmp
+
+WORKDIR /mocks
 
-# Create directory for output
-RUN mkdir -p /output
+ENV IMPOSTER_ENGINE=golang
 
 EXPOSE 8080
 
-# Default command shows help
-CMD ["imposter", "--help"]
+ENTRYPOINT ["imposter"]
+CMD ["--help"]

docs/docker.md

@@ -0,0 +1,31 @@
+# Docker
+
+You can run the Imposter CLI as a Docker container, without installing it locally.
+
+The container image is available at [`impostermocks/cli`](https://hub.docker.com/r/impostermocks/cli) on Docker Hub.
+
+## Start mocks
+
+To start a mock server using configuration in your current directory:
+
+```shell
+docker run --rm -v $PWD:/mocks -p 8080:8080 impostermocks/cli up
+```
+
+Your mock will be available at http://localhost:8080.
+
+## Scaffold configuration
+
+To generate mock configuration files in your current directory:
+
+```shell
+docker run --rm -v $PWD:/mocks impostermocks/cli scaffold
+```
+
+## Other commands
+
+You can pass any CLI command and flags after the image name:
+
+```shell
+docker run --rm -v $PWD:/mocks impostermocks/cli --help
+```