Load Balancers & ADC

An ADC is placed in the Data Center, closer to the Servers. ADC provides a single point of access for the clients that request information.

Application Delivery Controller (ADC) is the newer, fancier and more relevant term for Load Balancers. Although people refer to ADC as just a “Marketing Term”, ADCs certainly provide enhanced functionality compared to the Load Balancers of previous generation.

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Load Balancers:

  1. Layer 4 Devices
  2. Distribute Load across multiple servers. Load in the context of L4 devices point to TCP Connections (Socket – IP+Port Combination)
  3. Normally, full TCP stack is client facing and the server facing TCP stack can only handle up to L4
  4. Load Balancers don’t offer high performance functionality like caching, compression and newer protocols like SPDY
  5. Additional features like WAF, DoS prevention are not usually available.

Example: Cisco CSS

Application Delivery Controllers:

  1. Layer 7 Devices
  2. Distribute Load across multiple servers. Load in the context of L7 devices point to TCP Connections and L7 content like HTTP content.
  3. They tend to have 2 full TCP stack. One facing the client and another facing the servers. This provides them with the functionality of a full-proxy and enables them to balance application content and not just the L4 connections.
  4. Most ADC devices provide high performance functionality like caching, compression and newer protocols like SPDY
  5. Additional features like WAF, DoS prevention are usually available.

Example: F5 LTM, Citrix NetScaler

Reference:

Load Balancing 101 – The Evolution to Application Delivery Controllers

What is an Application Delivery Controller ?

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