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Application Delivery Controller | @CloudExpo #SDN #VM #AI #Virtualization
Part 1 - Application Delivery got its start in the form of network-based load balancing hardware
By: Peter Silva
Apr. 5, 2017 12:00 PM
A Little History
Figure 1: Network-based load balancing appliances.
With the advent of virtualization and cloud computing, the third iteration of ADCs arrived as software delivered virtual editions intended to run on hypervisors. Virtual editions of application delivery services have the same breadth of features as those that run on purpose-built hardware and remove much of the complexity from moving application services between virtual, cloud, and hybrid environments. They allow organizations to quickly and easily spin-up application services in private or public cloud environments.
Basic Application Delivery Terminology
Node, Host, Member, and Server
The second concept is a member (sometimes, unfortunately, also called a node by some manufacturers). A member is usually a little more defined than a server/node in that it includes the TCP port of the actual application that will be receiving traffic. For instance, a server named www.example.com may resolve to an address of 172.16.1.10, which represents the server/node, and may have an application (a web server) running on TCP port 80, making the member address 172.16.1.10:80. Simply put, the member includes the definition of the application port as well as the IP address of the physical server. We will refer to this as the service.
Why all the complication? Because the distinction between a physical server and the application services running on it allows the ADC to individually interact with the applications rather than the underlying hardware or hypervisor. A host (172.16.1.10) may have more than one service available (HTTP, FTP, DNS, and so on). By defining each application uniquely (172.16.1.10:80, 172.16.1.10:21, and 172.16.1.10:53), the ADC can apply unique load balancing and health monitoring based on the services instead of the host. However, there are still times when being able to interact with the host (like low-level health monitoring or when taking a server offline for maintenance) is extremely convenient.
Most load balancing-based technology uses some concept to represent the host, or physical server, and another to represent the services available on it— in this case, simply host and services.
Pool, Cluster, and Farm
The key element here is that all systems have a collective object that refers to “all similar services” and makes it easier to work with them as a single unit. This collective object—a cluster—is almost always made up of services, not hosts.
Putting It All Together
Figure 2: Application Delivery comprises four basic concepts—virtual servers, clusters, services, and hosts.
While the diagram above may not be representative of a real-world deployment, it does provide the elemental structure for continuing a discussion about application delivery basics.
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