Load Balancing and Failover Between Multiple Web Servers
In most environments, multiple web servers are used to balance load and provide high availability at the web server layer. A load balancer is typically required to direct user connections to participating web servers. For best performance and resilience, it is recommended that a hardware-based solution is used. A Load Balancing system such as Cisco ACE 4710 or the F5 BigIP LTM appliance is placed in front of a set of web servers. In this configuration, if there are also multiple InterSystems IRIS server instances, such as in a distributed cache cluster, each web server (and by implication, Web Gateway instance) should be configured to connect to a specific InterSystems IRIS® server instance.
Software based load-balancing and failover systems, though not as robust as hardware based solutions, are much less costly to deploy. Examples of software based solutions include HAProxy and the Apache Group’s mod_proxy_balancer. For more information, see the HAProxy site www.haproxy.orgOpens in a new tab
Important:
Persistent (“sticky”) sessions should always be enabled for web applications. It is essential that each user session “sticks” to the same back-end InterSystems IRIS server for the lifetime of the session – unless, of course, a failover event occurs.
Although the above approach is the primary recommendation, the Web Gateway provides a basic (software-based) system for implementing load balancing and failover between multiple InterSystems IRIS servers (that is, the CSP servers for multiple InterSystems IRIS instances). This facility is described in the following section.
