[deployment-guide/comm-rel: 99/727] Trac#552 and BZ612634 (failover doesn't handle multiple A records)

[Jaromir Hradilek]

commit 5a2437841bb86f8a43366038a71ba594d68f75d0
Author: David O'Brien <davido at redhat.com>
Date:   Thu Jul 22 16:47:07 2010 +1000

    Trac#552 and BZ612634 (failover doesn't handle multiple A records)

 en-US/SSSD.xml |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/en-US/SSSD.xml b/en-US/SSSD.xml
index a4f4864..5089492 100644
--- a/en-US/SSSD.xml
+++ b/en-US/SSSD.xml
@@ -393,10 +393,14 @@ simple_allow_users = user1, user2</screen>
           <para>For more information on SRV records, refer to <ulink url="http://tools.ietf.org/html/rfc2782">RFC 2782</ulink>.</para>
         </section>
 
-        <section>
+        <section id="sect-SSSD_User_Guide-Configuring_Domains-Configuring_Failover-How_the_Failover_Mechanism_Works">
           <title>How the Failover Mechanism Works</title>
           <para>The failover mechanism distinguishes between machines and services. The back end first tries to resolve the hostname of a given machine; if this resolution attempt fails, the machine is considered offline. No further attempts are made to connect to this machine for any other service. If the resolution attempt succeeds, the back end tries to connect to a service on this machine. If the service connection attempt fails, then only this particular service is considered offline and the back end automatically switches over to the next service. The machine is still considered online and might still be tried for another service.</para>
 
+          <para>
+            The failover mechanism does not handle DNS A records with multiple IP addresses; instead it only uses the first address. Further, providing multiple A records does not provide failover. Only the first A record is used, and if a lookup attempt on the first record fails then the system attempts no further lookups. To find multiple servers with a single request, and thus implementing failover, SSSD relies on SRV resource records, as explained in <xref linkend="sect-SSSD_User_Guide-Configuring_Domains-Configuring_Failover-Using_SRV_Records_with_Failover"/>.
+          </para>
+
           <para>Further connection attempts are made to machines or services marked as offline after a specified period of time; this is currently hard coded to 30 seconds. If there are no more machines to try, the back end as a whole switches to offline mode, and then attempts to reconnect every 30 seconds.</para>
         </section>