[master] 3eba5f8 warning and advise about backend proxy connections

Nils Goroll nils.goroll at uplex.de
Mon Apr 9 12:24:10 UTC 2018

commit 3eba5f8ce18e3d8e06a7016f9099e689f5186bc7
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Mon Apr 9 14:23:06 2018 +0200

    warning and advise about backend proxy connections
    Ref #2622

diff --git a/doc/sphinx/reference/vcl.rst b/doc/sphinx/reference/vcl.rst
index d2eec3d..d2263dc 100644
--- a/doc/sphinx/reference/vcl.rst
+++ b/doc/sphinx/reference/vcl.rst
@@ -252,6 +252,21 @@ parameters. The following attributes are available:
     The PROXY protocol version Varnish should use when connecting to
     this backend. Allowed values are ``1`` and ``2``.
+    *Notice* this setting will lead to backend connections being used
+    for a single request only (subject to future improvements). Thus,
+    extra care should be taken to avoid running into failing backend
+    connections with EADDRNOTAVAIL due to no local ports being
+    available. Possible options are:
+    * Use additional backend connections to extra IP addresses or TCP
+      ports
+    * Increase the number of available ports (Linux sysctl
+      ``net.ipv4.ip_local_port_range``)
+    * Reuse backend connection ports early (Linux sysctl
+      ``net.ipv4.tcp_tw_reuse``)
     Maximum number of open connections towards this backend. If
     Varnish reaches the maximum Varnish it will start failing

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