When talking of major websites which maintain a 100% uptime, eg: Amazon & Google to name a few, they comprise of thousands of servers. Google's Linux cluster alone currently processes over 150 million queries a day, searching a multi-terabyte web index for every query with an average response time of less than a quarter of a second, with near-100% uptime.
High-availability or Failover Server Clusters comprise of redundant nodes, used mainly for the accessibility of services which the cluster provides at times of failure in core system components, attempting to use redundancy of cluster components [multiple servers], abolishing single point of breakdown of the entire website. There are several commercial uses of High-Availability clusters for numerous operating systems. We have implemented Load Balanced architecture on various Linux platforms such as CentOS, RHEL and Debian.
Load-balancing clusters function by dispensing a workload consistently over several back end nodes. Normally the cluster will be configured with numerous redundant load-balancing front end servers. As each element in a load-balancing cluster has to offer full service, it can be considered of as an active/active HA cluster, where all accessible servers process requests.
Linux Load Balanced Server's Architecture
A typical Linux based Load Balanced servers' architecture consists of 2 or more similar configuration web servers and 2 database servers which are behind a Load Balancer or Master Server. Each web server will have a public IP assigned to it as well as an Internal LAN IP. After the implementation of Load Balancing routing rules on the Load Balancer, we configure Firewall rules to allow web traffic on the web servers to pass through the Load Balancer or Master Server. The Load Balancer/Master Server will then take care of equal distribution of traffic on each of the web servers who then pass on SQL queries to the database server. We implement realtime mirroring solution on 2 Database servers using Rsync and FAM modules.Any change on server 1 is reflected immediately on Database Server 2. If one of the Database Server in a cluster becomes unavailable as a result of failure or maintenance, another Database server immediately begins providing service within few seconds.The figure below will help you understand the typical Linux Load Balanced Architecure that eUKhost Offers:
