Add documentation for new 'backlog' config option

Signed-off-by: Andrew Clayton <[email protected]>

source/configuration.rst

@@ -99,6 +99,21 @@ Available listener options:
  defines SSL/TLS
  :ref:`settings <configuration-listeners-ssl>`.
 
+ * - **backlog**
+ - Integer;
+ controls the 'backlog' parameter to the listen(2) system-call.
+ This essentially limits the number of pending connections waiting
+ to be accepted.
+
+ The default varies by system. On Linux, FreeBSD, OpenBSD and macOS
+ we default (-1) to the OS's default. E.g. on Linux since 5.4 this is
+ 4096, on FreeBSD it's 128.
+
+ On other systems we default to 511.
+
+ NOTE: Whatever limit you set here will be limited by the OS's
+ system-wide sysctl, e.g. on Linux net.core.somaxconn and on BSD
+ kern.ipc.somaxconn
 
 Here, a local listener accepts requests at port 8300
 and passes them to the **blogs** app
@@ -5662,4 +5677,4 @@ Example with njs and the use of a template literal:
  "if": "`${uri == '/health' ? false : true}`",
  "path": "..."
  }
- }
+ }