split image build in to phases to install git on builder

Dockerfile

@@ -1,7 +1,26 @@
 # Define the build argument with no default value
-ARG PYTHON_VERSION
+ARG PYTHON_VERSION=3.10
 
-# Use the official Python image as the base image
+# Builder stage
+FROM python:${PYTHON_VERSION}-slim AS builder
+
+# hadolint ignore=DL3008
+RUN <<EOF
+    apt-get update
+    apt-get install --no-install-recommends -y git
+EOF
+
+# Set the working directory:
+WORKDIR /app
+
+# Copy and install dependencies:
+COPY requirements.lock ./
+RUN PYTHONDONTWRITEBYTECODE=1 pip install --no-cache-dir -r requirements.lock
+
+# Copy the application source code:
+COPY src .
+
+# Final stage
 FROM python:${PYTHON_VERSION}-slim
 
 # Define the build argument with a default value
@@ -16,12 +35,8 @@ LABEL maintainer="Carlos Martín (github.com/inean)"
 # Set the working directory:
 WORKDIR /app
 
-# Copy and install dependencies:
-COPY requirements.lock ./
-RUN PYTHONDONTWRITEBYTECODE=1 pip install --no-cache-dir -r requirements.lock
-
-# Copy the application source code:
-COPY src .
+# Copy dependencies and source code from the builder stage
+COPY --from=builder /app /app
 
 # Run the application:
 ENTRYPOINT ["python", "-m", "dns_synchub"]