Commit f22e93f0 authored by Marcin Siodelski's avatar Marcin Siodelski
Browse files

[5478] Described HA specific commands.

parent 4f190e97
......@@ -3475,6 +3475,99 @@ both the command and the response.
</para>
</section> <!-- end of ha-ctrl-agent-config -->
<section xml:id="ha-control-commands">
<title>Control Commands for High Availability</title>
<para>Even though the HA hook library is designed to automatically
resolve issues with DHCP service interruptions by redirecting the
DHCP traffic to a surviving server and synchronizing the lease
database when required, it may be useful for the administrator to
have control over the server behavior. In particular, it may be
useful be able to trigger lease database synchronization on demand.
It may also be useful to manually set the HA scopes that are being
served.</para>
<para>Note that the backup server can sometimes be used to handle
the DHCP traffic in case if both active servers are down. The backup
servers do not perform failover function automatically. Hence, in
order to use the backup server to respond to the DHCP queries,
the server administrator must enable this function manually.
</para>
<para>The following sections describe commands supported by the
HA hook library which are available for the administrator.
</para>
<section xml:id="ha-sync-command">
<title>ha-sync command</title>
<para>The <command>ha-sync</command> is issued to instruct the
server to synchronize the local lease database with the
selected peer. The database synchronization may be triggered for
both active and backup server type. The <command>ha-sync</command>
has the following structure (DHCPv4 server case):
<screen>
{
"command": "ha-sync",
"service": [ "dhcp4 "],
"arguments": {
"server-name": "server2",
"max-period": 60
}
}
</screen>
</para>
<para>
When the server receives this command it first disables the
DHCP service of the server from which it will be fetching leases,
i.e. sends <command>dhcp-disable</command> command to that server.
The <command>max-period</command> parameter specifies the maximum
duration (in seconds) for which the DHCP service should be disabled.
If the DHCP service is successfully disabled, the synchronizing
server will fetch leases from the remote server by issuing the
<command>lease4-get-all</command> command. When the lease database
synchronization is complete, the synchronizing server sends the
<command>dhcp-enable</command> to the peer to re-enable its
DHCP service.
</para>
</section> <!-- ha-sync-command -->
<section xml:id="ha-scopes-command">
<title>ha-scopes command</title>
<para>This command allows for modifying the HA scopes that the
server is serving. Consult <xref linkend="ha-load-balancing-config"/>
and <xref linkend="ha-hot-standby-config"/> to learn what scopes
are available for different HA modes of operation. The
<command>ha-scopes</command> command has the following structure
(DHCPv4 server case):
<screen>
{
"command": "ha-scopes",
"service": [ "dhcp4 "],
"arguments": {
"scopes": [ "ha_server1", "ha_server2" ]
}
}
</screen>
</para>
<para>This command configures the server to handle traffic from
both <command>ha_server1</command> and <command>ha_server2</command>
scopes. In order to disable all scopes specify an empty list:
<screen>
{
"command": "ha-scopes",
"service": [ "dhcp4 "],
"arguments": {
"scopes": [ ]
}
}
</screen>
</para>
</section> <!-- ha-scopes-command -->
</section> <!-- ha-control-commands -->
</section> <!-- end of high-availability-library -->
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="hooks-radius.xml"/>
......
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