Yellow Bricks

by Duncan Epping

vcdx

Layer 2 Adjacency for vMotion (vmkernel)

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Recently I had a discussion around Layer 2 adjacency for the vMotion(vmkernel interface) network. With that meaning that all vMotion interfaces, aka vmkernel interfaces, are required to be on the same subnet as otherwise vMotion would not function correctly.

Now I remember when this used to be part of the VMware documentation but that requirement is nowhere to be found anywhere. I even have a memory of documentation of the previous versions stating that it was “recommended” to have layer-2 adjacency but even that is nowhere to be found. The only reference I could find was an article by Scott Lowe where Paul Pindell from F5 chips in and debunks the myth, but as Paul is not a VMware spokes person it is not definitive in my opinion. Scott also just published a rectification of his article after we discussed this myth a couple of times over the last week.

So what are the current Networking Requirements around vMotion according to VMware’s documentation?

  • On each host, configure a VMkernel port group for vMotion
  • Ensure that virtual machines have access to the same subnets on source and destination hosts
  • Ensure that the network labels used for virtual machine port groups are consistent across hosts

Now that got me thinking, why would it even be a requirement? As far as I know vMotion is all layer three today, and besides that the vmkernel interface even has the option to specify a gateway. On top of that vMotion does not check if the source vmkernel interface is on the same subnet as the destination interface, so why would we care?

Now that makes me wonder where this myth is coming from… Have we all assumed L2 adjacency was a requirement? Have the requirements changed over time? Has the best practice changed?

Well one of those is easy to answer; no the best practice hasn’t changed. Minimize the amount of hops needed to reduce latency, is and always will be, a best practice. Will vMotion work when your vmkernels are in two different subnets, yes it will. Is it supported? No it is not as it has not explicitly gone through VMware’s QA process. However, I have had several discussions with engineering and they promised me a more conclusive statement will be added to our documentation and the KB in order to avoid any misunderstanding.

Hopefully this will debunk this myth that has been floating around for long enough once and for all. As stated, it will work it just hasn’t gone through QA and as such cannot be supported by VMware at this point in time. I am confident though that over time this statement will change to increase flexibility.

References:

VCDX Prep Workshop Powerpoint published…

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Just got noted that the Presentation of the VCDX 3 Preperation Workshop has been published. This Powerpoint presentation was given by John Arrasjid and Pang Chen during Partner Exchange and got a lot of great feedback. For everyone aiming to become a VCDX over the course of the upcoming months this is definitely a must read!

VCDX Defense Preparation

Preparation time
  • Plan on working a minimum of 30-40 hours to complete the application and supporting documentation.
Mandatory VDCX documentation
  • Architectural design document with diagrams and blueprints
  • Implementation and next steps documentation
  • Validation/test plans
  • Operational plan/guide
  • Installation and configuration instructions

VCAP is nice, but what about VCDX 4?

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Looking at the VMware education website you can guess what the steps are to become a VCDX4:

VCP4 → VCAP4-DCA → VCAP4-DCD → Approved Design → Successful Defense = VCDX4

Please keep in mind that I am just guessing here, and this is not an official statement. Updates on the VCDX section of the VMware website can be expected any time soon now. The big question of course is what about those who are already certified? What will the upgrade path be? Honestly, I don’t know… we will just have to wait and see.

[UPDATE]

The info has just been released (Thanks Eric “scoop” Sloof) and I guess I was right:

  1. Be a VMware Certified Professional on vSphere 4 (VCP4)
  2. Pass the VCAP – Datacenter Administration Exam
  3. Pass the VCAP – Datacenter Design Exam
  4. Submit a VCDX4-DCD Application that is accepted
  5. Successfully present and defend a VMware Infrastructure Design and Implementation Plan

The following VMware advanced courses are recommended for VCDX certification preparation but are not required:

VCDX Application Form

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I had many questions around this and was always told I was not allowed to “talk” about the Application Form and the requirements for the VCDX defense. Apparently this has changed as VMware just published it on MyLearn and it is available to anyone with a MyLearn account.

Now, I want to remind everyone that this Application Form is subject to change:

The final step in becoming a VMware Certified Design Expert is the VCDX Defense. In this step you will need to successfully complete an interview, project review, and design defense activity. The VCP3 certification, the VMware Enterprise Administration on VI3 Exam pass, and the VMware Design on VI3 Exam pass are all pre-requisites to theVCDX Application. Applications will not be accepted unless all pre-requsites have been met.

Anyone going through the process will benefit from reading the application form. The questions I had most where what the minimal set of deliverables are. Those can be found in the application form, but for your convenience have been listed below:

  1. VI Architecture Design. This document provides a complete design for the virtual inf rastructure and dependencies. It provides detailed specifications for all architectural components, as well as the decisions and justifications behind design choices. It includes architectural schematic diagrams (a.k.a Design Blueprints)
  2. VI Installation and Configuration Guidelines and Procedures. This document provides guidance on how the specified design will be put together. This document i s sometimes referred to as an “assembly and configuration guide.”
  3. VI Operational Verification. This document provides a test plan t o be used to validate an implementation using the design documents.
  4. VI Operational Procedures. This document provides steps and guidance on how to use an implemented architecture from an operator’s perspective. This document is sometimes referred to as “standard procedures.”
  5. Next Steps. This document summarizes design requirements, objectives and issues. It provides recommendations for proceeding with the implementation as a wrap-up to a typical design project.

If you are going through the process, read the application form! Keep in mind that filling it out will take time. Especially the section on Design Decisions where you will need to come up with a consideration, decision, justification and impact in several sections of which for instance Storage, Networking, Cluster Design and VM design.

For those who will be submitting their design: READ! If it say “a minimum of four” stick to that as anything less is a straight reject.

VCDX defense panels

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Just to let you guys know… VCDX defense panels are being scheduled. The invites for Melbourne went out this week and the ones for VMworld SF will follow soon I guess.

Defense interviews will be held during the following days:

  • July 5-9, Melbourne, Australia
  • August 23-27, San Francisco, CA
  • October 11-15, Copenhagen, Denmark
  • November (dates TBD), Boston, MA

Completed applications will be scheduled in the order received.

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