Remove dependencies after install to reduce image size

middleware/Dockerfile

@@ -1,20 +1,22 @@
 FROM python:3.8-slim
 ENV PYTHONUNBUFFERED 1
-RUN apt-get update
-RUN apt-get install -y build-essential gcc
 
 RUN python -m venv /opt/venv
 ENV PATH="/opt/venv/bin:$PATH"
 
-RUN python -m pip install --upgrade pip
-
-ENV PATH="/opt/venv/bin:$PATH"
-
 RUN mkdir /code
 WORKDIR /code
 COPY setup.py /code/
 COPY requirements.txt /code/
-RUN pip install -r requirements.txt
+
+RUN buildDeps='gcc build-essential' \
+    && apt update \
+    && apt install -y --no-install-recommends $buildDeps \
+    && rm -rf /var/lib/apt/lists/* \
+    && pip install -r requirements.txt \
+    && apt purge -y --auto-remove $buildDeps \
+    && rm -rf /var/lib/apt/lists/* \
+    && rm -rf /root/.cache
 
 COPY . /code/