VCDX Journey – Part 3 – Design Scenario

Part 3 of this series will go over the oft overlooked design scenario.

My advice with scenario is to (while keeping in mind I haven’t achieved the number yet):

• Listen carefully and keep prying out information from the panelists. They’re playing the role of customers, sometimes difficult customers. Maybe one of them won’t speak at all only to throw that wrench in when you’re about to clinch it. Watch out for that silent panelist 😉 If that wrench is thrown, tell them you’re going to erase a certain section of the whiteboard because the information you wrote on there is now irrelevant because of a changed requirement or a new constraint you’ve discovered as a result of that wrench. Make sure you put the change on the whiteboard, one, because they probably score you on based on what’s on the whiteboard to a large degree, and two, to guide you along with the changed requirement.
• Identify if different tiers/parts of the required solution have different SLAs, if they don’t tell you, you ask. If they say they’re unsure, tell them they need to be sure and walk them through to determining an SLA for that part of the application. Alternatively, make an assumption, say it aloud, write it down and say it’d need to be validated or clarified and turned into a concrete requirement. Tell them of the risks with making the assumptions, write them down, tell them of the likely mitigation and write it down. Talk talk talk talk.. The more the words come out of you, the more the scoring opportunities.
• Don’t detract from the need to design for those SLAs. It’s all about the SLAs, all about the business needs, not about the tech knobs. Keep things simple, if unsure of something, request the panelists for more information. You can ask them to Google something for you too, within reason though. Asking twice/thrice is probably okay, any more and you’re asking for trouble.
• Watch out for components that can perform availability functions without the need for the hardware to do it for them. If there’s application level clustering available, use that for satisfying RPO requirements. Say they are licensed for MongoDB or SQL AlwaysOn, use that instead of proposing a VSAN stretched cluster or traditional stretched storage. If the RPO required is say 30 mins, propose vSphere Replication. Roll with SRM if they require repeatable DR exercises for instance.
• Don’t go physical level unless asked (maybe the panel’s leading you down a rabbit warren or helping you score points?). Example, if asked to explain multi-NIC vMotion (because you chose to use it to satisfy a business need), do it but keep it at the logical level. If prodded for more information, which happened to me, I said – Guys, let’s keep the physical level details for subsequent meetings, I’m here to give you a logical design and given the scarcity of time, let’s keep it at the logical level. Lemme tell you this is probably okay to say since I didn’t get any feedback about it. They’re looking at how you guide customers. Own the damn room. Speak loudly and clearly, no murmuring. Within reason, don’t cut them off though. If they’re opening their mouths to say something, a scoring opportunity is being provided. A bone’s being thrown. Mr VCDX, Rene van den Bedem wrote this excellent blog post (must read this) about watching out for those bones being thrown. Be very attentive!
• Formulate a strategy that will help you extract the required information, one that will guide you through the 45 mins. My good friend and study crew wingman, Shady Ali ElMalatawey, wrote this very cool design scenario guide that I can’t provide without his approval, but at a high level and in no order, some of the things are:
  • Determine business objectives
  • Determine budgetary and technical constraints
  • Determine SLAs (per application type) and associated RPOs/RTOs
  • Determine maintenance windows (24×7 operation or not – sort of thing)
  • Determine if datacenters have been chosen, bandwidth within and amongst them
  • Determine if any components can be reused
  • Determine staff training requirements and existing skill sets
  • Determine if any licensing has already been bought
• Whiteboard, whiteboard, and do some more. Get one at home if you have to (I certainly did get a 2x1m one, see picture below).

This concludes my three-post blog series on my yet-unfulfilled journey towards this pinnacle of certification. Not knowledge nor learning because there’s no end to that.