Advanced load balancing

To handle the delivery of today's applications, a load balancer must provide the intelligence to always direct each request to the right server resource, along with the capability to continuously monitor the health of application and web servers.

Layer 4 load balancing

The ability to direct incoming client requests to the correct server resource based on layer 2-4 information (e.g., MAC/IP address and TCP port) is mandatory for all load balancers. Load balancers should also include health monitoring, session persistence, and network integration. The NetScaler load balancer delivers the industry’s broadest array of load balancing technologies, including:

Health monitoring

The NetScaler load balancer continuously monitors the availability and health of not only the server hardware, but also the state of back-end databases and applications. Network links, operating systems, and even individual application elements are also monitored by the NetScaler load balancer. Some load balancers simply provide basic ping, TCP, and UDP checks, but the NetScaler load balancer goes further to include scriptable health checks, dynamic server response times, and extended content verification (ECV.) The NetScaler load balancer ensures optimal load balancing of sessions to only those servers that are fully functional, preventing bottlenecks and needless session redirects.

Session persistence

The NetScaler load balancer manages persistence requirements for application sessions. This load balancing functionality is required for applications where state information is not automatically shared across a server farm, and each user session must be handled by the same server. Standard load balancers utilize source IP, cookies, and attribute hashing to ensure a sticky connection. The NetScaler load balancer goes further, supporting SSL ID, SIP CALLID, token-based, JSESSIONID, and other advanced routines—all integrated into a single load balancer policy.

Network integration

Most load balancers are generally compatible with the standard routing protocols, such as OSPF, RIP, and BGP, and with networking techniques including 802.3ad link aggregation and VLAN tagging. NetScaler load balancers go further, adding dynamic routing and IPv6 support. NetScaler load balancing techniques include not only standard round robin and least packets algorithms, but include server application state protocol (SASP), SNMP-provided metrics, and numerous hashing schemes.

Layer 7 load balancing

Also referred to as content switching, L7 load balancing is essentially an extension of the traffic distribution, health monitoring, and session persistence capabilities of layer 4 load balancers. The advantage is that load balancer decisions can also be based on application layer data. NetScaler load balancers redirect traffic not only based on attributes such as HTTP header, URI, SSL session ID, and HTML form data, but can use any payload value to make a load balancing decision. This difference enables the load balancer to improve datacenter efficiency by reducing duplication of server and database resources, leading to improved ROI. With the NetScaler load balancer, all of the services and components that comprise an application no longer need to be implemented on all of the server nodes present. Each physical system can now be tailored to the functions it will be supporting.

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