An interesting topic came up the other day between some of us in the cloud team, regarding whether Ephemeral Ports should be continued to be used with vCD deployments.
A colleague of mine Aidan Dalgleish (Senior Consultant, VMware TS Cloud Practice) kindly documented our discussions and wrote up the decisions. He can be found on LinkedIn.
Background
The topic of Portgroup binding was discussed and Ephemeral binding was selected as the preferred option for vCD created Portgroups for some of the following reasons:
* Due to the dynamic nature of vCloud Director it is often difficult to define how many devices will be connected to a given Portgroup
* Easy to code as there is no requirement to monitor and dynamically adjust the number of ports configured on the Portgroup as with Static/Dynamic
* Very flexible due to their being no requirement to define a number of ports and hence limited only by configuration maximums
Should Ephemeral ports still be used?
For any Portgroup backed network we should be defining Static/Dynamic binding over Ephemeral. The reasons for this are as follows:
* First and foremost scalability. With the introduction of vSphere 4.1 there is a significant difference with regards to scalability when using Static/Dynamic (5,000 Portgroups per vDS/vCenter) binding vs Ephemeral (1,016 Portgroups per vDS/vCenter) and a total of 20,000 ports. So if you were to only use Ephemeral then you would undoubtedly hit network scalability issues before anything else.
* When defining networks such as External networks, it could be argued we know something about the network. For example, given we know the size of the subnet, we can make an educated guess with regards to a sensible number of ports to define on the Portgroups.
The topic of Static vs Dynamic was discussed and it was agreed that Dynamic would be better than Static since a port is released when a VM is powered off as opposed to when the VM is removed from the Portgroup as with Static. This will offer a better capability given the dynamic nature of a Cloud infrastructure and the potential of there to a number of powered off workloads that could unnecessarily consume ports.
So to summarise:
* Always go for vSphere 4.1 over 4.0 in order to realise the significant network scalability benefits
* Where possible use Dyanmic Portgroups in order to make the best use of the increased scalability in 4.1 (maximum static/dynamic Portgroups vs Ephemeral Portgroups)
* There is no requirement to use Ephemeral Portgroups for portgroups created in vCenter, however vCD will currently only create portgroups that use ephemeral port binding.
But wouldn’t a more flexible environment required ephemeral at this point? Both VLAN backed and vCD-NI backed use Ephemeral and those happen to be the most flexible.
For the remaining “static” networks like External Networks I would agree that there is no point in using ephemeral, even better I would avoid using it as it would limit the network pool numbers