Last NLVMUG I was talking about stretched clusters. My presentation elaborated somewhat on how VMware NSX can help you deal with challenges that arise when deploying a stretched cluster solution. In this blogpost I want to have a closer look at this specific topic.
A quick understanding about what a stretched cluster solution actually is; it is a vSphere cluster configured in one vCenter instance containing an equal number of hosts from both sites. This allows for disaster avoidance (vMotion) and disaster recovery (vSphere HA) between two geographical separated sites. From the backend infrastructure perspective, your (synchronous replicated) storage and network solutions must span both sites.
Looking into network designs used for stretched clusters, you will typically face challenges like:
- How do you design for VM mobility over 2 sites, requiring Layer-2 networks between the 2 sites?
- Stretched Layer-2 networks (VLANs) introduce a higher risk of failure (think Layer-2 loops).
- How to properly segment applications and/or tenants (customers/business units)?
- Netwerk flows. What about your egress and ingress connections?
Let’s begin with how a VMware NSX install-base could look like if it is deployed within stretched cluster infrastructure.
Stretched cluster with NSX architecture
A stretched cluster with VMware NSX could look like the following logical overview.