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Diffstat (limited to 'src/man/lv/include/failover.xml')
| -rw-r--r-- | src/man/lv/include/failover.xml | 120 |
1 files changed, 120 insertions, 0 deletions
diff --git a/src/man/lv/include/failover.xml b/src/man/lv/include/failover.xml new file mode 100644 index 0000000..1e6d084 --- /dev/null +++ b/src/man/lv/include/failover.xml @@ -0,0 +1,120 @@ +<refsect1 id='failover'> + <title>FAILOVER</title> + <para> + The failover feature allows back ends to automatically switch to a different +server if the current server fails. + </para> + <refsect2 id='failover_syntax'> + <title>Failover Syntax</title> + <para> + The list of servers is given as a comma-separated list; any number of spaces +is allowed around the comma. The servers are listed in order of +preference. The list can contain any number of servers. + </para> + <para> + For each failover-enabled config option, two variants exist: +<emphasis>primary</emphasis> and <emphasis>backup</emphasis>. The idea is +that servers in the primary list are preferred and backup servers are only +searched if no primary servers can be reached. If a backup server is +selected, a timeout of 31 seconds is set. After this timeout SSSD will +periodically try to reconnect to one of the primary servers. If it succeeds, +it will replace the current active (backup) server. + </para> + </refsect2> + <refsect2 id='failover_mechanism'> + <title>The Failover Mechanism</title> + <para> + The failover mechanism distinguishes between a machine and a service. 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> + 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. + </para> + <para> + 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> + </refsect2> + <refsect2 id='failover_tuning'> + <title>Failover time outs and tuning</title> + <para> + Resolving a server to connect to can be as simple as running a single DNS +query or can involve several steps, such as finding the correct site or +trying out multiple host names in case some of the configured servers are +not reachable. The more complex scenarios can take some time and SSSD needs +to balance between providing enough time to finish the resolution process +but on the other hand, not trying for too long before falling back to +offline mode. If the SSSD debug logs show that the server resolution is +timing out before a live server is contacted, you can consider changing the +time outs. + </para> + <para> + This section lists the available tunables. Please refer to their description +in the <citerefentry> +<refentrytitle>sssd.conf</refentrytitle><manvolnum>5</manvolnum> +</citerefentry>, manual page. <variablelist> + <varlistentry> + <term> + dns_resolver_server_timeout + </term> + <listitem> + <para> + Time in milliseconds that sets how long would SSSD talk to a single DNS +server before trying next one. + </para> + <para> + Default: 1000 + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + dns_resolver_op_timeout + </term> + <listitem> + <para> + Time in seconds to tell how long would SSSD try to resolve single DNS query +(e.g. resolution of a hostname or an SRV record) before trying the next +hostname or discovery domain. + </para> + <para> + Default: 3 + </para> + </listitem> + </varlistentry> + <varlistentry> + <term> + dns_resolver_timeout + </term> + <listitem> + <para> + How long would SSSD try to resolve a failover service. This service +resolution internally might include several steps, such as resolving DNS SRV +queries or locating the site. + </para> + <para> + Noklusējuma: 6 + </para> + </listitem> + </varlistentry> + </variablelist> + </para> + <para> + For LDAP-based providers, the resolve operation is performed as part of an +LDAP connection operation. Therefore, also the +<quote>ldap_opt_timeout</quote> timeout should be set to a larger value than +<quote>dns_resolver_timeout</quote> which in turn should be set to a larger +value than <quote>dns_resolver_op_timeout</quote> which should be larger +than <quote>dns_resolver_server_timeout</quote>. + </para> + </refsect2> +</refsect1> |