Partial IP address logging in nginx

content/docs/software/nginx.adoc

@@ -32,3 +32,23 @@ server {
     return 301 $scheme://example.com$request_uri;
 }
 ----
+
+=== Logging only partial IP addresses
+
+This assumes nginx is behind a proxy that sends a trusted `X-Forwarded-For` header, but the
+same can easily be done with the remote IP directly.
+
+[source]
+----
+server {
+    map $http_x_forwarded_for $forwarded_anon {
+        ~(?P<ip>\d+\.\d+\.\d+)\.    $ip.0;
+        ~(?P<ip>[^:]+:[^:]+):       $ip::;
+        default                     0.0.0.0;
+    }
+
+    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
+                      '$status $body_bytes_sent "$http_referer" '
+                      '"$http_user_agent" "$forwarded_anon"';
+}
+----