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Chapter 6
Traffic Server Clusters
Virtual IP failover assures that if a node in the cluster fails, other nodes can assume the failed node’s
responsibilities. Traffic Server handles virtual IP failover in the following ways:
•
The
traffic_manager
process maintains cluster communication. Nodes automatically exchange
statistics and configuration information through multicast communication. If multicast heartbeats are not
received from one of the cluster nodes, the other nodes recognize it as down.
•
The
traffic_manager
process reassigns the IP addresses of the failed node to the remaining operational
nodes within approximately 30 seconds, so that service can continue without interruption.
•
The IP addresses are assigned to new network interfaces and the new assignment is broadcast to the local
network. The IP reassignment is done through a process called ARP rebinding.
What are virtual IP addresses?
Virtual IP addresses are really just IP addresses. They are called virtual addresses because they are not tethered
to particular machines and can rotate among nodes in a Traffic Server cluster.
It is common for a single machine to represent multiple IP addresses on the same subnet. This machine would
have a primary or real IP address bound to its interface card and also serve many more virtual addresses.
You can set up your user base to use a DNS round robin pointing at virtual IP addresses, as opposed to using
the real IP addresses of the traffic server machines.
Because virtual IP addresses are not bound to machines, a Traffic Server cluster can steal addresses from
inactive traffic server nodes and distribute those addresses among the remaining live nodes. Using a
proprietary management protocol, Traffic Server nodes communicate their status with their peers. If a node
fails, its peers notice the failure and quickly negotiate which of the remaining nodes will mask the fault by
taking over the failed node’s virtual interface.
Setting virtual IP address options
Traffic Server provides several configuration options for virtual IP addressing. You can:
•
Enable and disable virtual IP addressing (see
Enabling/disabling virtual IP addressing‚ on page 48
)
•
Add, modify, and delete virtual IP addresses (see
Adding and editing virtual IP addresses‚ on page 49
)
Enabling/disabling virtual IP addressing
You can turn virtual IP addressing on or off by using Traffic Manager or by editing a configuration file
manually. Both procedures are described below.
To enable/disable virtual IP addressing from Traffic Manager:
1. Access Traffic Manager from your browser (refer to
Accessing Traffic Manager‚ on page 8
).
2. On the Configure tab, click the Server button.
3. Scroll to the Virtual IP Addressing section of the Server Basics page (shown below).
4. Select Virtual IP: On to enable virtual IP addressing.
Select Virtual IP: Off to disable virtual IP addressing.
