Optimise nginx certbot example Dockerfile

nginx-certbot/Dockerfile

@@ -1,10 +1,14 @@
-FROM nginx
-RUN apt-get update && \
-    apt-get install -y certbot curl python-certbot-nginx && \
-    apt-get -y autoclean; apt-get -y autoremove; \
-    rm -rf /var/lib/apt/lists/*
+FROM nginx:stable
+LABEL maintainer="markus@martialblog.de"
+
+RUN set -ex; \
+        apt-get update && \
+        DEBIAN_FRONTEND=noninteractive \
+        apt-get install --no-install-recommends -y \
+        certbot curl python-certbot-nginx && \
+        apt-get -y autoclean; apt-get -y autoremove; \
+        rm -rf /var/lib/apt/lists/*
 
 COPY entrypoint.sh /entrypoint.sh
 RUN chmod 700 /entrypoint.sh
-
 CMD ["/entrypoint.sh"]