vCloud Director with NSX: Edge Cluster

I see more and more that new and existing vCloud Director deployments leverage NSX as the networking component instead of the legacy vShield / vCloud Network and Security (vCNS). The main reasons are the announced end-of-life for vCNS and the additional features that NSX brings to the table (although most of them are not yet tenant consumable in vCloud Director – as of version 5.6.4).

When deploying NSX with vCloud Director what new considerations should be included when designing the architecture? In this post I want to concentrate on the concept of the Edge Cluster.

What is Edge Cluster?

VMware has published very good NSX-V Network Virtualization Design Guide. This is very detailed document describing all NSX concepts as well as how they should be properly architected. The concept of Edge Cluster is discussed in quite a detail as well so let me just summarize here.

NSX overlay networks allow the creation of logical networks over an existing IP network fabric. This enables highly scalable network design using Leaf / Spine architecture where the boundary between L2 and L3 networks is at the rack level (leafs) and all communication between racks is L3 only going through a set of spine routers.

NSX spans logical network across all racks however in the end we need to connect virtual workloads from the logical networks to the outside physical world (WAN, Internet, colocated physical servers, etc.). These networks are represented by a set of VLAN networks and because we are not stretching L2 across the racks we cannot trunk them everywhere – so they are connected only to one (or two for redundancy) rack which thus become the Edge Cluster.

So the purpose of the Edge Cluster is to host virtual routers – Edge Service Gateways that provide the connectivity between the physical world (VLANs) and virtual world (VXLAN logical switchites). Note that it does not mean that every Edge Gateway needs to be deployed there. If an Edge Gateway provides connectivity between two VXLAN logical switches – it can be deployed anywhere as logical switches span all clusters.

vCloud Director Edges

vCloud Director deploys Edge VMs in order to provide Organization VDC or vApp connectivity. The actual deployment is done through vCNS or NSX Manager but it is vCloud Director who makes decision about placement and configuration of the Edges. vCloud Director Edge Gateway provides connectivity between one or more vCloud Director External Network and one or more Organization VDC Network. It is deployed inside Provider VDC in a special System VDC Resource Pool on a datastore belonging to the Org VDC default storage policy. vCloud Director placement engine selects the most appropriate cluster where the Edge Gateway VM will be deployed – based on which clusters belong to Provider VDC, what is their available capacity and most importantly their access to the right storage and external networks.

vApp Edges provide connectivity between an Organization VDC network and a vApp network. They always have only one external and one internal interface. They are also deployed by vCloud Director to the Provider VDC System VDC Resource Pool and exist only when the vApp is in deployed mode (Powered On).

Transport Zone

Transport Zone defines the scope of a VXLAN logical switch. It consists of one or more vSphere clusters. Transport Zone can be created manually, however vCloud Director automatically creates for each Provider VDC one Transport Zone which matches the clusters that are added to the Provider VDC and associates it with a VXLAN Network Pool. When Organization VDC is created by vCloud System Administrator a Network Pool must be assigned – all Organization VDC and vApp Networks will then have its scope.

Design Option I – Traditional

In the traditional network architecture Access/Aggregation/Core the L2/L3 boundary is at the aggregation switches. This means all racks connected to the same set of aggregation switches have access to the same VLANs and thus there is no need for an Edge Cluster as the Edge connecting VLAN with VXLAN based networks can run on any given rack. In vCloud Director it means that as long as the external networks (VLANs) are trunked to aggregation switches we do not need to worry about Edge placement. The set of racks (clusters) connected to the same aggregation domain usually map to a vCloud Director Provider VDC. The transport zone is then identical to the aggregation domain.

Traditional Access/Aggregation/Core architecture
Traditional Access/Aggregation/Core architecture


The drawback of such design is that Provider VDCs cannot span multiple aggregation domains.

Design Option II – Combined Edge/Compute Cluster

In case spine/leaf network architecture is used, VLANs backing vCloud Director external networks are trunked only to one cluster. In this design option we will call it Edge/Compute Cluster. As explained above vCloud Director placement engine will deploy Edge VMs to a cluster based on VLAN connectivity – therefore it will automatically place all Edge Gateways into the Edge/Compute cluster as this is the only cluster where the external connectivity (VLANs) exists. vCloud Director will however also opportunistically place regular tenant VMs into this cluster (hence its name Edge/Compute).

Spine/leaf with Edge/Compute Cluster

This design option has all the scale advantages of Spine/Leaf architecture however the possibility of tenant workloads taking limited space of Edge/Compute cluster is the drawback. There are two potential options how to remediate this:

  1. vCloud Director Edge Gateways are always deployed by vCloud System Administrator. He/she could make sure that prior Edge Gateway deployment there is enough capacity in the Edge/Compute cluster. If not some tenant workloads can be migrated away to another cluster – this must be done from within vCloud Director (Resource Pool / Migrate to option). Live migration is however possible only if the Edge/Compute Cluster shares the same VXLAN prepared vSphere Distributed Switch (vDS) with the other clusters and this requires at least four network uplinks on the Edge/Compute Cluster hosts (two uplinks for vDS with external VLANs and two uplinks for VXLAN vDS).
  2. Artificially limit the size of Edge/Compute Cluster so the placement engine does not choose it for regular tenant workloads. This can be done by leveraging Resource Pool which is created manually in the Edge/Compute cluster and attached to the Provider VDC instead of the whole cluster. Then an artificial limit is set by System Administrator and is increased only when a new Edge Gateway needs to be deployed.

Both options unfortunately provide significant operational overhead.

Design Option IIb – Combined Edge/Compute Cluster with Non-elastic VDC

While elastic Org VDC types (such are Pay-As-You-Go or Allocation type) can span multiple clusters what would be the impact of non-elastic VDC such as Reservation Pool in this design option?

In non-elastic Org VDC all tenant workloads are deployed into the primary Provider VDC resource pool. However Edge VMs can be deployed into secondary resource pools. This means as long as the Edge/Compute cluster is added as secondary Resource Pool into a Provider VDC this design option can still be used.

Spine/leaf with Edge/Compute Clsuter and non-elastic VDC

Design Option III – Dedicated Edge Cluster

This design option extends the previous one but in this case we will have dedicated Edge Cluster which is not managed by vCloud Director at all. We will also introduce new Edge Gateway type – Provider Edges. These are manually deployed by the service provider totally outside of vCloud Director into the Edge Cluster. Their external uplinks are connected to external VLAN based networks and internal interfaces are connected to transit VXLAN Logical Switch spanning all Compute and the Edge clusters (manually created transport zone with all clusters). The transit network(s) are then consumed by vCloud Director as External Network – note that little workaround is need to do so – read here.

The Provider Edges can provide all NSX functionality (dynamic routing protocols on external uplinks, L2 bridging, L2 VPN, etc.). They can scale as additional vCloud Director External Networks are added (current maximum in VCD 5.6 is 750 External Networks). The Edges deployed by vCloud Director then go into compute clusters as all their interfaces connect to VXLAN logical switches spanned everywhere in the Provider VDC.

Spine/leaf with Dedicated Edge Cluster
Spine/leaf with Dedicated Edge Cluster

Read vCloud Director with NSX: Edge Cluster (Part 2) here.

2 thoughts on “vCloud Director with NSX: Edge Cluster

  1. If you create dedicated Edge storage policies and place them only on the edge cluster you can eliminate the need for the Admin to place the edge. In our PoC the Edge cluster contains the Internet Uplinks and a unique storage policy, thus we can guarantee that any edge deployed lands on that specific cluster.

    1. Not sure what you mean by ‘dedicated’ Edge storage policy. As I mentioned Edges are placed on default storage policy of Org VDC. So you can create an Edge storage policy, assign it as default to OrgVDC and do not allocate any capacity but that will inconvenience the tenant as he will always need to switch the default storage policy to another when deploying VMs.

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