use multi-stage docker build for test and runtime

Author: codewitching

.github/workflows/ci.yml

@@ -36,6 +36,11 @@ jobs:
         run: |
           docker build -t flask-ci-app .
 
-      - name: Run tests inside Docker
+      - name: Run tests inside Docker (test stage)
         run: |
-          docker run --rm flask-ci-app pytest
+          docker build --target test -t flask-ci-test .
+          docker run --rm flask-ci-test
+
+      - name: Build production Docker image
+        run: |
+          docker build --target runtime -t flask-ci-app .

Dockerfile

@@ -1,12 +1,34 @@
-FROM python:3.12-slim
+# ================================
+# Stage 1: Test Stage
+# ================================
+FROM python:3.12-slim AS test-stage
 
 WORKDIR /app
+COPY requirements.txt requirements-dev.txt ./
+
+RUN pip install --no-cache-dir -r requirements.txt \
+    && pip install --no-cache-dir -r requirements-dev.txt
 
 COPY . .
+ENV PYTHONPATH=/app
+CMD ["pytest"]
 
-RUN pip install --no-cache-dir -r requirements.txt \
-    && pip install pytest
+# ================================
+# Stage 2: Production Stage 
+# ================================
+FROM python:3.12-slim AS runtime
+
+WORKDIR /app
+
+COPY requirements.txt ./    
+
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY app ./app
+COPY app.py ./
 
 ENV PYTHONPATH=/app
 
-CMD ["python", "app.py"]
+EXPOSE 5000
+
+CMD ["python", "app.py"]

requirements-dev.txt

@@ -0,0 +1 @@
+pytest