Periodic DNS resolution

common/etc/nginx/templates/default.conf.template

@@ -28,6 +28,11 @@ js_set $s3uri s3gateway.s3uri;
 server {
     include /etc/nginx/conf.d/gateway/server_variables.conf;
 
+    # Set the hostname to a variable to be used with proxy_pass so that we can
+    # re-resolve the hostname as described here:
+    # https://www.nginx.com/blog/dns-service-discovery-nginx-plus/#domain-name-variable
+    set $upstream_server ${S3_SERVER}:${S3_SERVER_PORT};
+
     # Don't display the NGINX version number because we don't want to reveal
     # information that could be used to find an exploit.
     server_tokens off;
@@ -136,7 +141,7 @@ server {
 
         error_page 404 @trailslashControl;
 
-        proxy_pass ${S3_SERVER_PROTO}://storage_urls$s3uri;
+        proxy_pass ${S3_SERVER_PROTO}://$upstream_server$s3uri;
 
         include /etc/nginx/conf.d/gateway/s3_location.conf;
     }
@@ -194,7 +199,7 @@ server {
         # Comment out this line to receive the error messages returned by S3
         error_page 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 420 422 423 424 426 428 429 431 444 449 450 451 500 501 502 503 504 505 506 507 508 509 510 511 =404 @error404;
 
-        proxy_pass ${S3_SERVER_PROTO}://storage_urls$s3uri;
+        proxy_pass ${S3_SERVER_PROTO}://$upstream_server$s3uri;
         include /etc/nginx/conf.d/gateway/s3listing_location.conf;
     }
 

common/etc/nginx/templates/resolver.conf.template

@@ -0,0 +1,2 @@
+# Use NGINX's non-blocking DNS resolution
+resolver ${DNS_RESOLVERS};