Use an upstream for reverse proxy so future modifications are simplified

installation/pleroma.nginx

@@ -9,6 +9,12 @@
 proxy_cache_path /tmp/pleroma-media-cache levels=1:2 keys_zone=pleroma_media_cache:10m max_size=10g
                  inactive=720m use_temp_path=off;
 
+# this is explicitly IPv4 since Pleroma.Web.Endpoint binds on IPv4 only
+# and `localhost.` resolves to [::0] on some systems: see issue #930
+upstream phoenix {
+    server 127.0.0.1:4000 max_fails=5 fail_timeout=60s;
+}
+
 server {
     server_name    example.tld;
 
@@ -72,9 +78,7 @@ server {
     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
 
     location / {
-        # this is explicitly IPv4 since Pleroma.Web.Endpoint binds on IPv4 only
-        # and `localhost.` resolves to [::0] on some systems: see issue #930
-        proxy_pass http://127.0.0.1:4000;
+        proxy_pass http://phoenix;
     }
 
     location ~ ^/(media|proxy) {
@@ -87,11 +91,11 @@ server {
         proxy_ignore_client_abort on;
         proxy_buffering    on;
         chunked_transfer_encoding on;
-        proxy_pass         http://127.0.0.1:4000;
+        proxy_pass         http://phoenix;
     }
 
     location /api/fedsocket/v1 {
         proxy_request_buffering off;
-        proxy_pass http://127.0.0.1:4000/api/fedsocket/v1;
+        proxy_pass http://phoenix/api/fedsocket/v1;
     }
 }