add healthcheck script

Dockerfile.linux.amd64

@@ -34,6 +34,6 @@ VOLUME /var/www/app/themes.local
 EXPOSE 80
 
 ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]
-HEALTHCHECK --interval=30s --timeout=10s --retries=5 CMD wget --quiet --tries=1 --spider http://localhost
+HEALTHCHECK --interval=30s --timeout=10s --retries=3 CMD /usr/local/bin/healthcheck.sh
 WORKDIR /var/www/app
 CMD []

overlay/usr/local/bin/healthcheck.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+
+set -eo pipefail
+URL=http://localhost
+
+wget --quiet --tries=1 --spider ${URL}
+[ $? -ne 0 ] && exit 1
+
+CONTENT=$(wget --quiet -O - ${URL})
+case "$CONTENT" in
+  *Exception*) exit 1 ;;
+esac
+
+exit 0