Overlay Networking for Hybrid Computing Environments

July 5, 2015 § Leave a comment

Working with clients in the cloud space one of the first things which stands out for me is the difference in how cloud adoption is approached. Primarily I see the born on the cloud type companies which are very comfortable with the idea of infrastructure as a service or traditional, enterprise type companies which are open to the idea, but still hesitate for whatever reason. For these latter cases, it is clear why a hybrid strategy can be appealing; leverage the best of both worlds, on premise infrastructure for certain workloads and cloud infrastructure for others. The caveat here is that adopting a hybrid strategy often has its own set of challenges due to the need to integrate two different environments.

One of these challenges includes networking as the on premise environment and the offsite cloud environment are on separate physical networks connected over Layer 3 routing protocols. Note that this is unique to a hybrid environment as public or private cloud environments often have all resources residing within the same network. This becomes a problem for multiple reasons such as the possibility for network addressing overlap, performance considerations of having workloads communicate over Layer 3, and the need to reconfigure the network when moving workloads across spaces. Additionally, these networks are maintained by separate teams as the client is responsible for on premise networking and linkages to the cloud environment while the cloud service provider, such as SoftLayer, is responsible for the underlying physical network in the datacenters.

Architectural Overview of Virtual Overlay Network on Physical Underlay Layer

Architectural Overview of Virtual Overlay Network on Physical Underlay Layer

Figure 1 from Virtual Environments Redbook

This is where virtualized overlay networks can be implemented. At a high level, by using technologies such as Software Defined Networking (SDN) and overlay protocols like VXLAN/NVGRE (read more here – specifically see Chapters 1 & 2), the client can create their own seemingly unified network over all their physically separate resources by using virtual networking infrastructure on top of the underlying physical networking infrastructure (as seen in Figure 1 above). This works by abstracting away the complex routing to the underlying network and creating a system of edge routers/nodes at each site. These edge routers create a virtual link with a corresponding edge router at another location and allow the resources to act like they are on the same physical network. This allows compute resources connected to these routers to communicate over Layer 2 when in reality the edge routers are encapsulating this traffic and moving it over the underlying Layer 3 network and decapsulating it once it reaches the corresponding edge router at the other site (see Figure 2 below). This means that no changes to the underlying physical network are required as resources are added or subtracted to the overlay layer used by the client for all their infrastructure needs.

Edge Node Communication Process over Physical Underlay

Edge Node Communication Process over Physical Underlay

Figure 2 based on Virtual Environments Redbook

As a summary, this technology allows for environments to be designed so that workloads act as though they are on the same physical network while taking advantage of all the benefits of cloud. The virtualization of the network is the next frontier of software defined environments and I believe that technologies such as overlay networks will make it easier for enterprise clients to adopt hybrid computing strategies.

This post was simply an introduction to the technology so please feel free to comment with any thoughts or questions.

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