Add dockerfile for building custom nginx container

Add entrypoint that calls envsubst ahead of starting nginx

nginx/Dockerfile

@@ -0,0 +1,10 @@
+FROM docker.io/library/nginx:latest
+
+ENV NEXTCLOUD_DOMAIN=example.com
+ENV NEXTCLOUD_PHP_FPM_HOST=php-fpm-nextcloud:9000
+ENV NEXTCLOUD_MAX_UPLOAD_SIZE=512M
+
+ADD nginx.conf.template /nginx.conf.template
+ADD docker-entrypoint.sh /docker-entrypoint.sh
+
+ENTRYPOINT ["sh", "-c", "/docker-entrypoint.sh"]

nginx/docker-entrypoint.sh

@@ -0,0 +1,16 @@
+#/usr/bin/env bash
+
+# This implementation is adapted from the solution proposed here:
+# https://stackoverflow.com/questions/21866477/nginx-use-environment-variables
+
+# envsubst will take the input and replace all references to environment
+# variables with their corresponding value. Because nginx uses the same
+# '$' prefix for its internal variables, we should explicitly define the
+# variables we want to replace rather than replacing all env vars.
+envsubst '
+$NEXTCLOUD_PHP_FPM_HOST
+$NEXTCLOUD_DOMAIN
+$NEXTCLOUD_MAX_UPLOAD_SIZE
+' < /nginx.conf.template > /etc/nginx/nginx.conf
+
+exec nginx -g 'daemon off;'