Scott Jensen is an Engineering Director and colleague of mine from Dell with deep networking and operations experience.  He had first hand experience deploying OpenStack and Hadoop and has a critical role in defining Dell’s Reference Architectures in those areas.  When I saw this writeup about cloud networking, I asked if it would be OK to share it with you.

Guest Post 1 of 2 by Scott Jensen:

Having a basis in enterprise data center networking, Cloud computing I have many conversations with customers implementing a cloud infrastructure.  Their design the networking infrastructure can and should be different from a classic network configuration and many do not understand why.  Either due to a lack of knowledge in networking or due to a lack of understanding as to why cloud computing is different from virtualization.  Once you have an understanding of both of these areas you can begin to see why emerging technologies such as SDN (Software Defined Networking) and NFV (Network Function Virtualization) begin to address some of the issues that Cloud Computing can cause with your network.

Networking is all about traffic flows.  In order to properly design your infrastructure you need to understand where traffic is originating, where it is going and how much traffic will be following a specific route and at what times.

There are many differences between Cloud Computing and virtualization.  In many cases people I will talk to think of Cloud as virtualization in a different environment.  Of course this will work just fine however it does not take advantage of the goodness that a Cloud infrastructure can bring.  Some of the major differences between Virtualization and Cloud Computing have profound effects on how the network is utilized.  This all has to do with the application.  That is really what it is all about anyway.  Rob Hirschfeld has a great post on the difference between Pets and Cattle which describes this well.

Pets and Cattle as a workload evolution

In typical virtualized infrastructures, the applications have a fairly common pattern.  Many people describe these as Pets and are managed largely the same as a physical system.  They have a name, they are one of a kind, they are cared for, and when the die it can be traumatic (I know I have been there).

• They run on large stateful VMs
• They have a lifecycle which is typically very long such as years
• The applications themselves are not designed to tolerate failures.  Other technologies are brought in to ensure uptime.
• The application is scaled up when demands increase.  This is done by adding more memory or CPU to the VM.

Cloud applications are different.  Some people describe them as cattle and they are treated like cattle in many ways.  They do not necessarily have a name and if one dies it is sad but not a really big deal.  We should probably figure out what killed it but life goes on.

• They run on smaller stateless VMs
• They have a lifecycle measured in hours or months.  Sometimes even less than an hour.
• The application is designed to expect failures
• The application scales out by increasing the number of instances which is running when the demand increases.

In his follow-up post next week, Scott discusses how this impacts the network and how SDN and NFV promises to help.