Traffic Server Clusters; Understanding Traffic Server Clusters; Management-Only Clustering; Full Clustering - HP P4535A - Web Cache Server Appliance Administrator's Manual

6 Traffic Server Clusters

Traffic Server scales from a single node to multiple nodes that form a cluster, allowing you to improve system
performance and reliability.
This chapter discusses the following topics:
Understanding Traffic Server clusters‚ on page 45
Changing clustering mode‚ on page 46
Adding and deleting nodes in a cluster‚ on page 46
Virtual IP failover‚ on page 47

Understanding Traffic Server clusters

A Traffic Server cluster consists of multiple Traffic Server nodes. The nodes in a cluster share configuration
information and can form a single logical cache.
Traffic Server detects the addition and deletion of nodes in the cluster automatically and can detect when a
node is down. When the Virtual IP failover feature (described in
the live nodes in a cluster can assume a failed node's responsibilities.
Traffic Server has two clustering modes:
Management-only mode (refer to "Management-only clustering" on page 45 )
Full-clustering mode (refer to "Full clustering" on page 45 )

Management-only clustering

In management-only clustering mode, Traffic Server cluster nodes share configuration information. You can
administer all the nodes at the same time.
Traffic Server uses a multicast management protocol to provide a single system image of your Traffic Server
cluster. Information about cluster membership, configuration, and exceptions is shared across all nodes and
the
traffic_manager

Full clustering

In full-clustering mode, as well as sharing configuration information, a Traffic Server cluster distributes its
cache across its nodes into a single, virtual object store, rather than replicating the cache node by node. Traffic
Server can provide an enormous aggregate cache size and can maximize cache hit rate by storing objects only
once across the entire cluster.
A fully-clustered Traffic Server maps objects to specific nodes in the cluster. When a node receives a request,
it checks to see if the request is a hit somewhere in the cluster. If the request is a hit on a different node, the
node handling the request fetches the object from the hit node and serves it to the client. Traffic Server uses a
proprietary inter-node communication protocol to fetch an object from sibling cluster nodes.
If a node fails or is shut down and removed, Traffic Server removes references to the missing node on all nodes
in the cluster. If virtual IP failover (described in
for the missing node are handled by another node.
process automatically propagates configuration changes to all the nodes.
Virtual IP failover‚ on page
Virtual IP failover‚ on page
47) is enabled, requests destined
47) is enabled,
45