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+ <chapter id="system-integration"><title>System integration</title>
+ <para>
+ You may want to integrate conntrackd into your system in order to build
+ a robust firewall cluster. You should take a look at how the linux
+ distro of your choice does this, as there are some interesting things
+ to take into account.
+ </para>
+ <para>
+ Depending on the architecture of the firewall cluster, you may want to
+ sync each node after a fallback operation, so the new node
+ inmediately knows the connection of the other. This is specially
+ interesting in <emphasis>Active-Active</emphasis> mode.
+ </para>
+ <para>
+ This can be done using <emphasis>conntrackd -n</emphasis> just after
+ the new node has joined the conntrackd cluster, for example at boot
+ time. These operations require the main conntrackd daemon to open the
+ UNIX socket to receive the order from the
+ <emphasis>conntrackd -n</emphasis> call.
+ </para>
+ <para>
+ Care must be taken that no race conditions happens (i.e, the UNIX
+ socket is actually opened before <emphasis>conntrackd -n</emphasis> is
+ launched). Otherwise, you may end with a new node (after fallback)
+ which doesn't know any connection states from the other node.
+ </para>
+ <para>
+ Since <emphasis>conntrack-tools 1.4.4</emphasis>, the conntrackd
+ daemon includes integration with <emphasis>libsystemd</emphasis>. If
+ conntrackd is configured at build time with this support
+ (using <emphasis>--enable-systemd</emphasis>), then you can
+ use <emphasis>Systemd on</emphasis> in the
+ <emphasis>conntrackd.conf</emphasis> main configuration file.
+ To benefit from this integration, you should use a systemd service file
+ of <emphasis>Type=notify</emphasis>, which also includes support for
+ the systemd watchdog.
+ </para>
+ <para>
+ Using systemd and conntrackd with libsystemd support and a service file
+ of Type=notify means that conntrackd will notify of its readiness to
+ systemd, so you can launch <emphasis>conntrackd -n</emphasis> safely,
+ avoiding such race conditions.
+ </para>
+ </chapter>