Commit 4123fe53 authored by Yann Ylavic's avatar Yann Ylavic
Browse files

Follow up to r1789220. 

Document the implicit behaviour of ListenCoresBucketsRatio when multiple
Listen-ers are configured on the same IP:port.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1792675 13f79535-47bb-0310-9956-ffa450edef68
parent c527a6fe

docs/manual/mod/mpm_common.xml

+21 −0
Original line number Diff line number Diff line
@@ -300,6 +300,27 @@ in *BSDs.</compatibility> 
    <directive module="mpm_common">MaxSpareThreads</directive> lower bound values.

    The number of children processes needs to be a multiple of the number 

    of buckets to optimally accept connections.</p>



    <note>

    <title>Multiple <directive>Listen</directive>ers or Apache HTTP servers on

    the same IP address and port</title>

    <p>Setting the <code>SO_REUSEPORT</code> option on the listening socket(s)

    consequently allows multiple processes (sharing the same <code>EUID</code>,

    e.g. <code>root</code>) to bind to the the same IP address and port,

    without the binding error raised by the system in the usual case.</p>

    <p>This also means that multiple instances of Apache httpd configured on a

    same <code>IP:port</code> and with a positive <directive>ListenCoresBucketsRatio</directive>

    would start without an error too, and then run with incoming connections

    evenly distributed accross both instances (this is NOT a recommendation or

    a sensible usage in any case, but just a notice that it would prevent such

    possible issues to be detected).</p>

    <p>Within the same instance, Apache httpd will check and fail to start if

    multiple <directive>Listen</directive> directives on the exact same IP (or

    hostname) and port are configured, thus avoiding the creation of some

    duplicated buckets which would be useless and kill performances.  However

    it can't (and won't try harder to) catch all the possible overlapping cases

    (like a hostname resolving to an IP used elsewhere).</p>

    </note>

</usage>

</directivesynopsis>