explicitly set resolver in the nginx container (configurable envvar)

.docker/web-nginx/Dockerfile

@@ -15,6 +15,9 @@ ENV APP_WEB_ROOT=${APP_WEB_ROOT:-/var/www/html}
 # Base location for tt-rss (defaults to /tt-rss)
 ENV APP_BASE=${APP_BASE:-/tt-rss}
 
+# Resolver for nginx (kube-dns.kube-system.svc.cluster.local for k8s)
+ENV RESOLVER=${RESOLVER:-127.0.0.11}
+
 # In order to make tt-rss appear on website root without /tt-rss/ set above as follows in .env:
 # APP_WEB_ROOT=/var/www/html/tt-rss
 # APP_BASE=

.docker/web-nginx/nginx.conf

@@ -16,6 +16,8 @@ http {
 
 	index index.php;
 
+	resolver ${RESOLVER} valid=5s;
+
 	upstream app {
 		server ${APP_UPSTREAM}:9000;
 	}