diff --git a/server/Dockerfile b/server/Dockerfile
new file mode 100644
index 0000000..74297e8
--- /dev/null
+++ b/server/Dockerfile
@@ -0,0 +1,8 @@
+# Minimal sovereign WebSocket relay image for the lego-builder rooms.
+# Only needs `ws` — none of the React/build deps.
+FROM node:20-alpine
+WORKDIR /app
+RUN npm init -y >/dev/null 2>&1 && npm pkg set type=module >/dev/null 2>&1 && npm install ws@8 >/dev/null 2>&1
+COPY server ./server
+EXPOSE 8090
+CMD ["node", "server/index.js"]