add healthcheck for http services

webmails/rainloop/Dockerfile

@@ -3,7 +3,7 @@ FROM php:7.2-apache
 ENV RAINLOOP_URL https://github.com/RainLoop/rainloop-webmail/releases/download/v1.12.1/rainloop-community-1.12.1.zip
 
 RUN apt-get update && apt-get install -y \
-      unzip python3 python3-jinja2 \
+      unzip python3 python3-jinja2 curl \
  && rm -rf /var/www/html/ \
  && mkdir /var/www/html \
  && cd /var/www/html \
@@ -29,3 +29,5 @@ EXPOSE 80/tcp
 VOLUME ["/data"]
 
 CMD /start.py
+
+HEALTHCHECK CMD curl -f -L http://localhost/ || exit 1