The following reply was made to PR docs/186464; it has been noted by GNATS.
From: Allan Jude
To: bug-follo...@freebsd.org
Cc:
Subject: Re: docs/186464: Online-Documentation for carp(4) is outdated
Date: Wed, 12 Feb 2014 18:03:38 -0500
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Attached is a diff to bring the carp(4) section of the handbook up to date.
It pulls the conceptual stuff out into a section before the
instructions, and provides separate instructions for 9.x and prior, and
10.x and later.
Also adds some of the newer markup, like
--
Allan Jude
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Index: advanced-networking/chapter.xml
===
--- advanced-networking/chapter.xml(revision 43884)
+++ advanced-networking/chapter.xml(working copy)
@@ -5589,15 +5589,16 @@
-Common Address Redundancy Protocol
- (CARP)
+
+ Common Address Redundancy Protocol
+ (CARP)
+
TomRhodesContributed
by
+
AllanJudeUpdated
by
-
-
CARP
@@ -5607,135 +5608,280 @@
The Common Address Redundancy Protocol
(CARP) allows multiple hosts to share the
- same IP address. In some configurations,
- this may be used for availability or load balancing. Hosts
- may use separate IP addresses, as in the
- example provided here.
+ same IP address(es) and can be used to
+ achieve high availability. Hosts should also have a unique
+ IP address for management and configuration,
+ as in the example provided here.
-To enable support for CARP, the &os;
- kernel can be rebuilt as described in
with the following option:
+
+ Using CARP for High
+ Availability
-devicecarp
+ One use of CARP is to provide server
+ high availability for one or more services. This example
+ configures failover support for three hosts, all with
+ unique IP addresses and providing the same
+ web content. These machines are load balanced with a Round
+ Robin DNS configuration. The master and
+ backup machines should be configured identically other than
+ their hostnames and management IP
+ addresses. These servers need to run the same services, such
+ as the web server, with the same configuration so that when
+ the failover happens, requests to that service will be
+ answered correctly and with the same content. The failover
+ machine has two additional CARP interfaces,
+ one for each of the master content server's
+ IP addresses. When a failure occurs, the
+ failover server will pick up the failed machine's
+ IP address. This means that the failure
+ should go completely unnoticed by the user. This example has
+ two different masters named
+ hosta.example.org and
+ hostb.example.org respectively, with
+ a shared slave named
+ hostc.example.org.
-Alternatively, the if_carp.ko module
- can be loaded at boot time. Add the following line to
- /boot/loader.conf:
+ Each virtual address has a unique
+ identification number known as a Virtual Host IDentification
+ (VHID) which is used to distinguish the
+ virtual address across the various failover machines that
+ share the address on the network.
-if_carp_load="YES"
+
-CARP functionality should now be
- available and may be tuned via several &man.sysctl.8;
- variables:
+
+ Using CARP on &os; 10 and
+ Later
-
-
-
-
- OID
- Description
-
-
+ To enable support for CARP, load the
+ carp.ko kernel module by adding the
+ following line to
+ /boot/loader.conf:
-
-
- net.inet.carp.allow
- Accept incoming CARP packets.
-Enabled by default.
-
+ carp_load="YES"
-
- net.inet.carp.preempt
- This option downs all of the
-CARP interfaces on the host when one
-goes down. Disabled by default.
-
+ Alternatively, the &os; kernel can be rebuilt as
+ described in with the following
+ option:
-
- net.inet.carp.log
- A value of 0 disables any
-logging. A value of 1 enables
-logging of bad CARP packets. Values
-greater than 1 enable logging of
-state changes for the CARP
-
