diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
new file mode 100644
index 0000000..f5717f2
--- /dev/null
+++ b/.github/workflows/build.yml
@@ -0,0 +1,73 @@
+name: Build Docker image
+
+on:
+  push:
+    branches: [master]
+  workflow_dispatch:
+
+env:
+  REGISTRY: docker.io
+  IMAGE_NAME: ${{ github.repository }}
+
+permissions:
+  contents: read
+
+jobs:
+  build-group:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        target:
+          - ruby-0.x-2.0
+          - ruby-1.2-1.9
+          - ruby-2.1-2.4
+          - ruby-2.5-2.7
+          - ruby-3.0-3.2
+          - ruby-3.3-4.0
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKER_USER }}
+          password: ${{ secrets.DOCKER_PASS }}
+
+      - name: Build ${{ matrix.target }}
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          target: ${{ matrix.target }}
+          cache-from: |
+            type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:cache-${{ matrix.target }}
+          cache-to: |
+            type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:cache-${{ matrix.target }},mode=max
+
+  build-final:
+    needs: build-group
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKER_USER }}
+          password: ${{ secrets.DOCKER_PASS }}
+
+      - name: Build and push final image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          tags: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:latest
+          cache-from: |
+            type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:cache-ruby-0.x-2.0
+            type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:cache-ruby-1.2-1.9
+            type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:cache-ruby-2.1-2.4
+            type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:cache-ruby-2.5-2.7
+            type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:cache-ruby-3.0-3.2
+            type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:cache-ruby-3.3-4.0
diff --git a/Dockerfile b/Dockerfile
index b1b1de8..9c1e1d7 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,10 +4,14 @@ ARG variant=-slim
 ARG mirror=http://deb.debian.org/debian
 ARG system_ruby=ruby2.7
 
-# Build for 0.*, 1.0*, 1.1*, 1.8 and 1.8.5
-FROM debian:buster-slim
+# rake -j interpret non-numeric argument as number of CPUs plus 3.
+ARG j=numcpu_plus_alpha
+
+# =============================================================================
+# Base build environment: Debian Buster (for legacy Ruby versions)
+# =============================================================================
+FROM debian:buster-slim AS builder-buster
 ENV DEBIAN_FRONTEND=noninteractive
-ARG mirror
 
 RUN echo "deb http://archive.debian.org/debian/ buster main contrib non-free" > /etc/apt/sources.list && \
     echo "deb http://archive.debian.org/debian-security/ buster/updates main contrib non-free" >> /etc/apt/sources.list && \
@@ -17,7 +21,7 @@ RUN dpkg --add-architecture i386 \
   && echo "deb-src http://archive.debian.org/debian/ buster main" > /etc/apt/sources.list.d/deb-src.list \
   && echo 'Dpkg::Use-Pty "0";\nquiet "2";\nAPT::Install-Recommends "0";' > /etc/apt/apt.conf.d/99autopilot \
   && echo 'Acquire::HTTP::No-Cache "True";' > /etc/apt/apt.conf.d/99no-cache \
-  && apt-get update \
+  && apt-get update -o Acquire::Check-Valid-Until=false \
   && apt-get install \
       build-essential \
       gcc-multilib \
@@ -36,20 +40,25 @@ COPY lib/ruby_version.rb /all-ruby/lib/
 COPY patch /all-ruby/patch/
 RUN rake setup_build
 
-# rake -j interpret non-numeric argument as number of CPUs plus 3.
+# =============================================================================
+# Ruby 0.x, 1.0, 1.1, 1.8.0-1.8.5, 2.0.0 on Debian Buster
+# =============================================================================
+FROM builder-buster AS ruby-0.x-2.0
 ARG j=numcpu_plus_alpha
 
-COPY versions/0.* versions/1.* versions/2.0.0* /all-ruby/versions/
+COPY versions/0.* versions/1.0* versions/1.1* versions/1.8.0* versions/1.8.1* versions/1.8.2* versions/1.8.3* versions/1.8.4* versions/1.8.5* versions/2.0.0* /all-ruby/versions/
 RUN rake -j ${j} all-0 all-1.0 all-1.1a all-1.1b all-1.1c all-1.1d all-1.8 all-1.8.5
 RUN rake -j ${j} all-2.0.0
 
-RUN rm -rf Rakefile versions/ patch/
-RUN rm -rf DIST build/*/log build/*/ruby*/
-RUN rm -rf build/*/man build/*/share/man build/*/share/doc build/*/share/ri
-RUN rm -f build/*/lib/libruby-static.a
-RUN rm -f build/*/bin/gcc build/*/bin/cc
+RUN rm -rf Rakefile versions/ patch/ DIST build/*/log build/*/ruby*/ \
+      build/*/man build/*/share/man build/*/share/doc build/*/share/ri && \
+    rm -f build/*/lib/libruby-static.a build/*/bin/gcc build/*/bin/cc
+RUN find /build-all-ruby -type f \( -name ruby -o -name '*.so' \) -exec sh -c 'file $1 | grep -q "not stripped"' - '{}' \; -print0 | xargs -0 strip
 
-FROM ${os}:${version}${variant}
+# =============================================================================
+# Base build environment: Debian Bullseye (for modern Ruby versions)
+# =============================================================================
+FROM ${os}:${version}${variant} AS builder-bullseye
 ENV DEBIAN_FRONTEND=noninteractive
 ARG mirror
 ARG version
@@ -71,9 +80,6 @@ RUN dpkg --add-architecture i386 \
   && apt-get build-dep ${system_ruby} \
   && rm -rf /var/lib/apt/lists/*
 
-COPY --from=0 /build-all-ruby/ /build-all-ruby
-COPY --from=0 /all-ruby/ /all-ruby
-
 WORKDIR /all-ruby
 
 COPY Rakefile /all-ruby/
@@ -81,52 +87,96 @@ COPY lib/ruby_version.rb /all-ruby/lib/
 COPY patch /all-ruby/patch/
 RUN rake setup_build
 
-# rake -j interpret non-numeric argument as number of CPUs plus 3.
+# =============================================================================
+# Ruby 1.2-1.8.7, 1.9.x
+# =============================================================================
+FROM builder-bullseye AS ruby-1.2-1.9
 ARG j=numcpu_plus_alpha
 
-COPY versions/1.* versions/2.1* versions/2.2* versions/2.3* versions/2.4* versions/2.5* versions/2.6* versions/2.7* versions/3.0* /all-ruby/versions/
+COPY versions/1.2* versions/1.3* versions/1.4* versions/1.6* versions/1.8.6* versions/1.8.7* versions/1.9* /all-ruby/versions/
 RUN rake -j ${j} all-1.2 all-1.3 all-1.4 all-1.6 all-1.8.6 all-1.8.7
 RUN rake -j ${j} all-1.9.0 all-1.9.1 all-1.9.2
 RUN rake -j ${j} all-1.9.3
-RUN rake -j ${j} all-2.1
-RUN rake -j ${j} all-2.2
-RUN rake -j ${j} all-2.3
-RUN rake -j ${j} all-2.4
-RUN rake -j ${j} all-2.5
-RUN rake -j ${j} all-2.6
-RUN rake -j ${j} all-2.7
-RUN rake -j ${j} all-3.0
 
-COPY versions/3.1* /all-ruby/versions/
-RUN rake -j ${j} all-3.1
+RUN rm -rf Rakefile versions/ patch/ DIST build/*/log build/*/ruby*/ \
+      build/*/man build/*/share/man build/*/share/doc build/*/share/ri && \
+    rm -f build/*/lib/libruby-static.a build/*/bin/gcc build/*/bin/cc
+RUN find /build-all-ruby -type f \( -name ruby -o -name '*.so' \) -exec sh -c 'file $1 | grep -q "not stripped"' - '{}' \; -print0 | xargs -0 strip
 
-COPY versions/3.2* /all-ruby/versions/
-RUN rake -j ${j} all-3.2
+# =============================================================================
+# Ruby 2.1-2.4
+# =============================================================================
+FROM builder-bullseye AS ruby-2.1-2.4
+ARG j=numcpu_plus_alpha
 
-COPY versions/3.3* /all-ruby/versions/
-RUN rake -j ${j} all-3.3
+COPY versions/2.1* versions/2.2* versions/2.3* versions/2.4* /all-ruby/versions/
+RUN rake -j ${j} all-2.1 all-2.2 all-2.3 all-2.4
 
-COPY versions/3.4* /all-ruby/versions/
-RUN rake -j ${j} all-3.4
+RUN rm -rf Rakefile versions/ patch/ DIST build/*/log build/*/ruby*/ \
+      build/*/man build/*/share/man build/*/share/doc build/*/share/ri && \
+    rm -f build/*/lib/libruby-static.a build/*/bin/gcc build/*/bin/cc
+RUN find /build-all-ruby -type f \( -name ruby -o -name '*.so' \) -exec sh -c 'file $1 | grep -q "not stripped"' - '{}' \; -print0 | xargs -0 strip
 
-COPY versions/3.5* /all-ruby/versions/
-RUN rake -j ${j} 3.5.0-preview1
+# =============================================================================
+# Ruby 2.5-2.7
+# =============================================================================
+FROM builder-bullseye AS ruby-2.5-2.7
+ARG j=numcpu_plus_alpha
 
-COPY versions/4.0* /all-ruby/versions/
-RUN rake -j ${j} all-4.0
+COPY versions/2.5* versions/2.6* versions/2.7* /all-ruby/versions/
+RUN rake -j ${j} all-2.5 all-2.6 all-2.7
 
-COPY lib/* /all-ruby/lib/
-COPY all-ruby /all-ruby/
+RUN rm -rf Rakefile versions/ patch/ DIST build/*/log build/*/ruby*/ \
+      build/*/man build/*/share/man build/*/share/doc build/*/share/ri && \
+    rm -f build/*/lib/libruby-static.a build/*/bin/gcc build/*/bin/cc
+RUN find /build-all-ruby -type f \( -name ruby -o -name '*.so' \) -exec sh -c 'file $1 | grep -q "not stripped"' - '{}' \; -print0 | xargs -0 strip
+
+# =============================================================================
+# Ruby 3.0-3.2
+# =============================================================================
+FROM builder-bullseye AS ruby-3.0-3.2
+ARG j=numcpu_plus_alpha
 
-RUN rm -rf Rakefile versions/ patch/
-RUN rm -rf DIST build/*/log build/*/ruby*/
-RUN rm -rf build/*/man build/*/share/man build/*/share/doc build/*/share/ri
-RUN rm -f build/*/lib/libruby-static.a
-RUN rm -f build/*/bin/gcc build/*/bin/cc
+COPY versions/3.0* versions/3.1* versions/3.2* /all-ruby/versions/
+RUN rake -j ${j} all-3.0 all-3.1 all-3.2
 
+RUN rm -rf Rakefile versions/ patch/ DIST build/*/log build/*/ruby*/ \
+      build/*/man build/*/share/man build/*/share/doc build/*/share/ri && \
+    rm -f build/*/lib/libruby-static.a build/*/bin/gcc build/*/bin/cc
 RUN find /build-all-ruby -type f \( -name ruby -o -name '*.so' \) -exec sh -c 'file $1 | grep -q "not stripped"' - '{}' \; -print0 | xargs -0 strip
+
+# =============================================================================
+# Ruby 3.3-4.0
+# =============================================================================
+FROM builder-bullseye AS ruby-3.3-4.0
+ARG j=numcpu_plus_alpha
+
+COPY versions/3.3* versions/3.4* versions/3.5* versions/4.0* /all-ruby/versions/
+RUN rake -j ${j} all-3.3 all-3.4 3.5.0-preview1 all-4.0
+
+RUN rm -rf Rakefile versions/ patch/ DIST build/*/log build/*/ruby*/ \
+      build/*/man build/*/share/man build/*/share/doc build/*/share/ri && \
+    rm -f build/*/lib/libruby-static.a build/*/bin/gcc build/*/bin/cc
+RUN find /build-all-ruby -type f \( -name ruby -o -name '*.so' \) -exec sh -c 'file $1 | grep -q "not stripped"' - '{}' \; -print0 | xargs -0 strip
+
+# =============================================================================
+# Aggregator: Combine all build outputs and deduplicate with rdfind
+# (rdfind is already installed in builder-bullseye)
+# =============================================================================
+FROM builder-bullseye AS aggregator
+
+COPY --from=ruby-0.x-2.0 /build-all-ruby/ /build-all-ruby/
+COPY --from=ruby-1.2-1.9 /build-all-ruby/ /build-all-ruby/
+COPY --from=ruby-2.1-2.4 /build-all-ruby/ /build-all-ruby/
+COPY --from=ruby-2.5-2.7 /build-all-ruby/ /build-all-ruby/
+COPY --from=ruby-3.0-3.2 /build-all-ruby/ /build-all-ruby/
+COPY --from=ruby-3.3-4.0 /build-all-ruby/ /build-all-ruby/
+
 RUN rdfind -makehardlinks true -makeresultsfile false /build-all-ruby
 
+# =============================================================================
+# Final: Runtime image
+# =============================================================================
 FROM ${os}:${version}${variant}
 ENV DEBIAN_FRONTEND=noninteractive
 ARG mirror
@@ -159,7 +209,15 @@ RUN dpkg --add-architecture i386 \
       ${system_ruby} \
   && rm -rf /var/lib/apt/lists/*
 
-COPY --from=1 /build-all-ruby/ /build-all-ruby
-COPY --from=1 /all-ruby/ /all-ruby
+COPY --from=aggregator /build-all-ruby/ /build-all-ruby/
+COPY --from=ruby-0.x-2.0 /all-ruby/ /all-ruby/
+COPY --from=ruby-1.2-1.9 /all-ruby/bin/ /all-ruby/bin/
+COPY --from=ruby-2.1-2.4 /all-ruby/bin/ /all-ruby/bin/
+COPY --from=ruby-2.5-2.7 /all-ruby/bin/ /all-ruby/bin/
+COPY --from=ruby-3.0-3.2 /all-ruby/bin/ /all-ruby/bin/
+COPY --from=ruby-3.3-4.0 /all-ruby/bin/ /all-ruby/bin/
+
+COPY lib/* /all-ruby/lib/
+COPY all-ruby /all-ruby/
 
 WORKDIR /all-ruby