4
Chapter 1
Overview
•
Host reliability and availability information (to avoid making the user wait for non-functional servers)
The DNS Resolver
Traffic Server includes a fast, asynchronous DNS resolver to streamline conversion of host names to IP
addresses. Traffic Server implements the DNS resolver natively, directly issuing DNS command packets,
rather than relying on slower, conventional resolver libraries. Many DNS queries can be issued in parallel and
a fast DNS cache maintains popular bindings in memory, significantly reducing DNS traffic.
Traffic Server processes
Traffic Server contains three processes that work together to process Traffic Server requests and manage,
control, and monitor the health of the Traffic Server. The three processes are described below:
•
The
traffic_server
process is the transaction processing engine of Traffic Server. It is responsible for
accepting connections, processing protocol requests, and serving documents from the cache or origin
server.
•
The
traffic_manager
process is the command and control facility of the Traffic Server, responsible for
launching, monitoring, and reconfiguring the
traffic_server
process. The
traffic_manager
process is also responsible for Traffic Manager, the proxy auto configuration port, the statistics interface,
cluster administration, and virtual IP failover.
If the
traffic_manager
process detects a
traffic_server
process failure, it instantly restarts the
process but also maintains a connection queue of all incoming requests. All incoming connections that
arrive in the several seconds before full server restart are saved in the connection queue and processed in
first-come, first-served order. This connection queueing shields users from any server restart downtime.
•
The
traffic_cop
process monitors the health of both the
traffic_server
and
traffic_manager
processes. The
traffic_cop
process periodically (several times each minute) queries the
traffic_server
and
traffic_manager
process by issuing heartbeat requests to fetch synthetic web
pages. In the event of failure (if no response is received within a time-out interval or if an incorrect
response is received),
traffic_cop
restarts the
traffic_manager
and
traffic_server
processes.
Figure 1-1. illustrates the three Traffic Server processes.
Figure 1-1. Traffic Server processes
crontab process ensures
that traffic_cop process
is running
traffic_server
traffic_manager
traffic_cop
operating
system
Traffic
Server
Processes
Traffic Server Node