feat: Add custom Docker build for package registry

Dockerfile.custom-registry

@@ -0,0 +1,71 @@
+# This image contains the package-registry binary AND a pre-warmed set of packages.
+
+ARG GO_VERSION=1.25.7
+ARG BUILDER_IMAGE=golang
+ARG RUNNER_IMAGE=cgr.dev/chainguard/wolfi-base
+
+# STAGE 1: Build the 'distribution' tool
+FROM --platform=${BUILDPLATFORM:-linux} ${BUILDER_IMAGE}:${GO_VERSION} AS distribution-builder
+WORKDIR /src
+COPY . .
+ARG TARGETPLATFORM
+# Build the distribution binary inside its own directory
+RUN make -C cmd/distribution release-${TARGETPLATFORM:-linux/amd64}
+
+
+# STAGE 2: Run the 'distribution' tool to download packages
+FROM distribution-builder AS packager
+# Copy the custom configuration for the packages we want
+COPY ./cmd/distribution/examples/custom-packages.yaml .
+# Run the tool. It will create the packages in 'build/distribution/'
+RUN ./cmd/distribution/distribution ./cmd/distribution/examples/custom-packages.yaml
+
+
+# STAGE 3: Build the final 'package-registry' binary
+FROM --platform=${BUILDPLATFORM:-linux} ${BUILDER_IMAGE}:${GO_VERSION} AS registry-builder
+WORKDIR /src
+COPY . .
+ARG TARGETPLATFORM
+# Build the main package-registry binary from the root directory
+RUN make release-${TARGETPLATFORM:-linux/amd64}
+
+
+# STAGE 4: Final image assembly
+FROM ${RUNNER_IMAGE}
+
+# Get dependencies (same as original Dockerfile)
+# Mailcap is installed to get mime types information.
+RUN if grep -q "Red Hat" /etc/os-release ; then \
+    microdnf install -y mailcap zip rsync && \
+    microdnf clean all ; \
+  else \
+    apk update && \
+    apk add mailcap zip rsync curl && \
+    rm -rf /var/cache/apk/* ; \
+  fi
+
+WORKDIR /package-registry
+
+# Copy the main binary from the 'registry-builder' stage
+COPY --from=registry-builder /src/package-registry .
+
+# --- THIS IS THE KEY STEP ---
+# Copy the downloaded packages from the 'packager' stage into the final image
+# The registry is configured to look for packages in '/packages/package-registry/'
+COPY --from=packager /src/build/distribution/. /packages/package-registry/
+
+# Get in config which expects packages in /packages
+COPY config.docker.yml ./config.yml
+
+# Run as non-root user
+USER 1000
+
+# Start registry when container is run an expose it on port 8080
+EXPOSE 8080
+ENTRYPOINT ["./package-registry"]
+
+# Make sure it's accessible from outside the container
+ENV EPR_ADDRESS=0.0.0.0:8080
+
+HEALTHCHECK --interval=1s --retries=30 CMD curl --silent --fail localhost:8080/health || exit 1
+

README.md

@@ -165,6 +165,39 @@ If you want to run the most recent registry for development, run the main tag.
 
 These images contain only the package registry, they don't contain any package.
 
+#### Build a Custom Docker Package Registry Image
+
+The official Docker container for the Elastic Package Registry includes all available packages for every Kibana version. For development or specific deployments, you might want to build a custom, smaller container that only includes packages compatible with your target Kibana environment. This results in a much smaller image footprint.
+
+To build your own custom Elastic Package Registry container image, follow these steps:
+
+1.  **Define Your Package Set**: Create or modify the `cmd/distribution/examples/custom-packages.yaml` file to specify the desired package versions. You can filter by `kibana.version`, `spec.max`, and other criteria. All the available settings are documented in the distribution [README](./cmd/distribution/README.md)
+
+2.  **Build the Image**: Run the following command from the root of the repository to build your custom image.
+
+> **Note**: If you use a different configuration file than the default, remember to update the `Dockerfile.custom-registry` accordingly.
+
+```bash
+docker build --build-arg GO_VERSION="$(cat .go-version)" -f Dockerfile.custom-registry -t custom-package-registry .
+```
+
+**Example: Smaller Image Footprint**
+
+Here is an example of a custom image built with packages compatible with Kibana `>8.18.0` & `>9.0.0`. The resulting image is significantly smaller than the default one.
+
+```bash
+ docker images
+
+IMAGE                            ID             DISK USAGE   CONTENT SIZE   EXTRA
+custom-package-registry:latest   193b9b282bf2       1.61GB          631MB       
+```
+
+You can run your custom registry with the following command:
+
+```bash
+docker run --rm -it -p 8080:8080 custom-package-registry
+```
+
 ### Testing with Kibana
 
 The Docker image of Package Registry is just an empty distribution without any packages.

cmd/distribution/examples/custom-packages.yaml

@@ -0,0 +1,22 @@
+# Base address of the Package Registry
+address: "https://epr.elastic.co"
+
+# Queries are executed with each one of the parameters of the matrix.
+matrix:
+  - spec.max: 3.5
+  - prerelease: true
+    spec.max: 3.5
+
+# Queries to execute to discover packages >8.18.0 & >9.0.0.
+queries:
+  - kibana.version: 8.18.0
+    spec.max: 3.4
+  - kibana.version: 9.0.0
+    spec.min: 2.3
+    spec.max: 3.4
+
+
+actions:
+  - print:
+  - download:
+      destination: ./build/distribution