Add multistage build to backend, reducing size by about 4 MB

backend/Dockerfile

@@ -1,20 +1,37 @@
+#########################################
+# MULTI-STAGE BUILD CONTAINER - Builder #
+#########################################
+
 # Base image
-FROM node:alpine
+FROM node:alpine AS builder
 
 # Make folder to put our files in
 RUN mkdir -p /usr/src/app
 RUN mkdir -p /usr/src/app/backend
 
-# Set working directory so that all subsequent command runs in this folder
+# Set working directory so that all subsequent commands run in this folder
 WORKDIR /usr/src/app/backend
 
-# Copy package json and install dependencies
+# Copy package.json, package-lock.json and install dependencies
 COPY package*.json ./
 RUN npm ci
 
 # Copy our app
 COPY . .
 
+############################################
+# MULTI-STAGE BUILD CONTAINER - Production #
+############################################
+
+# Base image
+FROM node:alpine
+
+# Set working directory
+WORKDIR /usr/src/app/backend
+
+# Copy all required app files from builder to production container
+COPY --from=builder /usr/src/app/backend/ ./
+
 # Expose port to access server
 EXPOSE 5000