Refactor Dockerfile to set environment variables for upstream server, cache size, and DNS resolver

Author: Robbie1977

Dockerfile

@@ -3,6 +3,10 @@ FROM nginx:1.26-alpine
 LABEL maintainer="VirtualFlyBrain"
 LABEL description="NGINX caching proxy for Owlery"
 
+ENV UPSTREAM_SERVER=owl.virtualflybrain.org:80
+ENV CACHE_MAX_SIZE=20g
+ENV DNS_RESOLVER="8.8.8.8 1.1.1.1"
+
 ARG NGINX_CONF=nginx.conf.template
 COPY $NGINX_CONF /etc/nginx/nginx.conf.template
 COPY health-monitor.sh /usr/local/bin/health-monitor.sh
@@ -12,4 +16,4 @@ RUN mkdir -p /var/cache/nginx && chown -R nginx:nginx /var/cache/nginx && \
 
 EXPOSE 80
 
-CMD ["/bin/sh", "-c", "UPSTREAM_SERVER=${UPSTREAM_SERVER:-owl.virtualflybrain.org:80} CACHE_MAX_SIZE=${CACHE_MAX_SIZE:-20g} DNS_RESOLVER=${DNS_RESOLVER:-8.8.8.8 1.1.1.1} envsubst '${UPSTREAM_SERVER} ${CACHE_MAX_SIZE} ${DNS_RESOLVER}' < /etc/nginx/nginx.conf.template > /etc/nginx/nginx.conf && /usr/local/bin/health-monitor.sh & nginx -g 'daemon off;'"]
+CMD ["/bin/sh", "-c", "envsubst '${UPSTREAM_SERVER} ${CACHE_MAX_SIZE} ${DNS_RESOLVER}' < /etc/nginx/nginx.conf.template > /etc/nginx/nginx.conf && /usr/local/bin/health-monitor.sh & nginx -g 'daemon off;'"]