You will often hear or see the term North-South vs East-West when looking at networks. Let’s take a quick look at what people mean when they use these terms.
North South traffic is often referred to as traffic than needs to traverse into or out of your network, So for example as you sit reading this you are using north south traffic to access this web page over the Internet. Also the server hosting this site will also be using north south traffic to deliver the content.
Historically north-south traffic was the predominant traffic flow within a network with the bulk of data being outside of the local network. This is indeed still the case where your data center is being hosted externally or with a web based service.
east-west traffic on the other hand focusses on traffic that flows from server to server, such as application to database for example. The east-west traffic flow has increased over the last few years with the introduction of “big data” and other marketing buzzwords. The key differentiator however between north-south traffic is that east-west traffic never leaves the data center.
What about APIs
When network engineers talk about north-south it’s fair to say they are not always referring to the traffic. Northbound or Southbound can be used as a reference to an API. So if this comes up from an API standpoint, always look at it from the applications perspective, so if we take a cloud service a Northbound API would represent how the end user interacts with the cloud. A Southbound API on the other hand would refer to the interaction between the actual infrastructure, allowing programmatic control of hardware and software, for example compute will leverage storage using a southbound API.