Refactor the docker file for build/run stage

Dockerfile

@@ -1,10 +1,49 @@
-FROM ubuntu:24.04
+FROM ubuntu:24.04 AS build-image
 
-RUN apt-get update && apt-get upgrade -y && apt-get install python3-pip tini -y && apt-get clean
+RUN apt-get update && \
+    apt-get upgrade -y && \
+    apt-get install python3-venv python3-dev gcc git -y && \
+    rm -rf /var/lib/apt/lists/*
 
-COPY ./requirements.txt /opt/os-capacity/requirements.txt
-RUN pip install -U -r /opt/os-capacity/requirements.txt
+# build into a venv we can copy across
+RUN python3 -m venv /opt/venv
+ENV PATH="/opt/venv/bin:$PATH"
 
-COPY ./os_capacity/prometheus.py /opt/os-capacity/prometheus.py
+COPY ./requirements.txt /os-capacity/requirements.txt
+RUN pip install -U pip setuptools
+RUN pip install --requirement /os-capacity/requirements.txt
+
+COPY . /os-capacity
+RUN pip install -U /os-capacity
+
+#
+# Now the image we run with
+#
+FROM ubuntu:24.04 AS run-image
+
+RUN apt-get update && \
+    apt-get upgrade -y && \
+    apt-get install --no-install-recommends python3 tini ca-certificates -y && \
+    rm -rf /var/lib/apt/lists/*
+
+# Copy accross the venv
+COPY --from=build-image /opt/venv /opt/venv
+ENV PATH="/opt/venv/bin:$PATH"
+
+# Create the user that will be used to run the app
+ENV APP_UID=1001
+ENV APP_GID=1001
+ENV APP_USER=app
+ENV APP_GROUP=app
+RUN groupadd --gid $APP_GID $APP_GROUP && \
+    useradd \
+      --no-create-home \
+      --no-user-group \
+      --gid $APP_GID \
+      --shell /sbin/nologin \
+      --uid $APP_UID \
+      $APP_USER
+
+USER $APP_UID
 ENTRYPOINT ["tini", "--"]
-CMD ["python3", "-u", "/opt/os-capacity/prometheus.py"]
+CMD ["os_capacity"]