Netscaler is an Application delivery controller which is used for Load balancing, Http compression, SSL Offloading(which is useful for web servers),content switching, application acceleration, application firewall and more.

A NetScaler appliance is usually deployed in front of a server farm and functions as a transparent TCP proxy between clients and servers, without requiring any client-side configuration.(Basically L4-L7 web Application Delivery Controller too..)

Available as a physical or virtual appliance, Citrix NetScaler is an application delivery controller that:

• Accelerates internal and external-facing applications up to five times.
• Optimizes application availability through advanced Layer-4 through Layer-7 traffic management.
• Increases security with an integrated application firewall.
• Substantially lowers costs by increasing web server efficiency.

Citrix NetScaler is a comprehensive system deployed in front of application and database servers that combines high-speed load balancing and content switching with:

• Application acceleration
• Highly-efficient data compression
• Static and dynamic content caching
• SSL acceleration
• Network optimization
• Application performance monitoring
• Robust application security

By Citrix: “Citrix NetScaler makes apps and cloud-based services run five times better by offloading app and database servers, accelerating app and service performance, and integrating security. Deployed in front of web and database servers, NetScaler combines high-speed load balancing and content switching, data compression, content caching, SSL acceleration, network optimization, application visibility and application security on a single, comprehensive platform."

Netscaler improves performance by sitting between client and server using application switching, traffic management, and connection multiplexing.

Some of the netscaler features include:

Connection multiplexing, application firewall, authentication authorization and auditing (AAA), content filter, content switching, HTTP compression, integrated caching, load balancing, netscaler gateway, rewrite and ssl offloading.  Most used netscaler features: GSLB, Layer 4 and Layer 7, surge protection and traffic domains.

Netscaler manageability features – admin partitions, action analytics, appexpert, appflow, command center, insight center. All these features are available with all editions of netscaler. Command center and insight centers should be installed as a separate vms.

Netscaler key benefits:

Netscaler performs application-specific traffic analysis to distribute, optimize and secure layer 4 through layer 7 network traffic for web applications using

• Acceleration: improve performance using client and server tcp optimizations, appcompress and appcache.
• Availability: improve application availability using load balancing and content switching, ipv6 support, traffic domains, gslb, surge protection and priority queuing.
• Security: Provide security and authentication using L4 and L7 Dos Defences, L7 rewrite and responder, AAA for traffic management, netscaler appfirewall with xml security, netscaler cloudbridge connector.

Front-End and TCP protocol optimization:

• Domain Sharding: enables browsers to open more parallel connections by modifying embedded URLs with sub-domains to trick the browser into opening more parallel connections. It is useful and effective on high latency/bandwidth networks like mobile clients.
• Image optimization: images consume lot of space on web page. Image optimization reduces page size significantly resulting in improved page download and render times. Adaptive image sizing can result in better and small images which are downloaded faster. Image conversion can reduce the size and bandwidth consumption on the network.
• Inlining: simplifies processing and reduces download time on client devices. Java script and css elements are injected into html document inline, corresponding to where they are called.
• Minification: process of removing all unnecessary characters and space from javascript and css files. This reduces size of the response significantly and at times by more than 30%.

Tcp multiplexing: default feature of netscaler. When a user to netscaler page, netscaler grabs the details and contacts the backend server (lets say web server). When second user connects to netscaler requesting connection to the same backend server, netscaler connects/contacts the backend server on the same TCP connection. This way multiple users connect to same web server over single tcp connection. This will reduce the number of tcp connections to the server, inturn reducing resource utilization on the web server. Also, since netscaler is using same tcp connection, it connects much faster to user.

Tri-Scale Technology:

Driven by the demand from enterprises to achieve this powerful yet economic scaling, TriScale technology gives the flexibility to Scale Up, Scale Out, Scale In, or any combination of the three.

• Scale Up – The “Pay-as-you-Grow” license allows a customer to buy for example 100Mbps of performance and incrementally add licenses as needed all the way up to 500Mbps of performance.  The elasticity in this solution also allows for burst packs – the ability to add extra capacity for a set period of time to get through a predicted spike in traffic such as a holiday season or the end of a financial period.
• Scale Out – As even more capacity is needed, rather than a requirement for a complex, disruptive and costly forklift upgrade, the capacity can be expanded further by simply adding a new appliance into the cluster. Unlike competitive clustering offerings where there are really multiple applications running on separate boxes acting as a backup to each other, the Citrix TriScale clustering enables multiple appliances to act as one big powerful platform so that a single application or multiple applications can use the combined power of the multiple appliances to deliver incremental capacity. One of the other main advantages of Citrix clustering is that it gives a great alternative to an HA pair. By using a cluster rather than an HA pair, you keep the resilience but eliminate idle resources and get higher performance and capacity. You are also now set up to expand almost without limit by simply adding more NetScaler’s as needed.
• Scale In – For datacenters where consolidation is key, NetScaler SDX enables up to 115 fully isolated NetScaler instances to run on a single appliance, allowing more efficient utilization and consolidation of resources. NetScaler SDX offers complete isolation between independent instances, and more than double the consolidation density of competing solutions.  Combined with Scale-up and Scale out, this becomes an incredibly dynamic and powerful solution.

In short form, Tri-Scale technology works as Bandwidth control with scale UP, capacity control with scale OUT, multi-tenancy with scale IN. With data predicted by Analysts to grow at a rate of 50x in the next decade,  Citrix Tri-Scale technology has you covered whichever way you need to scale; up, out, in or any combination.

Reduced Total Cost of Ownership:

Netscaler eliminates need of extensive back end resources, and reduces the total cost of ownership by:

• Using features such as caching, compression, SSL and TCP Offloading.
• Automatically direct requests with content to cache farm.
• Providing N-tier multilayer load balancing support of cache servers.
• Reducing server load, which enables fewer servers to do more.