TheSaffaGeek

My ramblings about all things technical

VCAP-CID Objective 1.4 – Determine Availability Requirements for a Conceptual Design

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Knowledge

Identify availability options for management components.

  • Availability can achieved within the vCloud architecture in a number of different ways and via differing methods. I’m going to break them up into different categories and i’m not going to cover each one but if you understand the different methods I think when you are reading the vCAT or any other kind of design book you’ll be able to identify them with ease.
    • Redundancy: This is simply creating multiple instances of an important service to ensure that if one or more fail that the solution isn’t impacted by this. There are multiple examples of this but the most simple but one of the most important in my opinion is the creation and usage of multiple vCloud cells to ensure load balancing but more importantly redundancy in the event of a loss of a vCloud cell. You can also cover this further down the stack with Heartbeat in the vSphere layer(even though this has now been made end of life) ,multiple network cards from the physical networking and multiple redundant switches to multiple redundant storage processors.
    • Disaster Recovery/Failover: This is covered in a whole section in the vCAT which goes over methods of utilising products like SRM to configure disaster recovery of the management layer. For conceptual this is more about knowing what is and isn’t possible but also taking the availability requirements of the customer from a business impact analysis where it is deemed the amount of money a customer is willing to lose due to downtime and then equate this to a number of nines. The table below gives an example of the number of times compared to amount of downtime and with the larger the number of nines this will then mean more expensive solutions which you will need to advise your customer about (99.9 can be met by HA for example but 99.99 will require heartbeat and synchronise replication with QoS). For conceptual you don’t cover specific products but knowing that you will need a DR site with fast links between will cover this for example.

HA

Differentiate between management components and resource components.

  • This is simply determining what should be part of your management cluster and what should be part of your resource cluster. I think this is really straight forward as anything in your management cluster is used to provide services to you the vCloud administrator and the resource cluster/s are for your customers to provision to and is the pools of resources you configure as your provider virtual datacentres. The below image is a great example of a conceptual diagram of the management and resource clusters.

conceptual

Skills and Abilities

Explain compatibility of various vSphere high availability features with a vCloud design.

  • This is covered perfectly in appendix A of the vCAT Architecting a VMware vCloud pdf so I don’t see the need to explain it here and i think it is better if you go through that instead. The link to the online documentation centre is here 

Given customer requirements and constraints, determine appropriate customer Service Level Agreements (SLAs) for the conceptual design.

  • This is covered in more depth within objective 1.6 so we will cover this in that section.

Determine how given SLAs impact availability design decisions.

  • This is covered in more depth within objective 1.6 so we will cover this in that section.

Given customer requirements and constraints, determine how to achieve desired availability.

  • From the design workshops and requirements collecting you will have worked out what the customers requirements and constraints are and will then have to work with these to try meet them all. For this it is their availability requirements which will be as I mentioned above their permitted amount of downtime per year along with their RPO’s ,RTO’s , MTD’s and WRT’s. From this you will have to work with their constraints to design a solution that meets their requirements so for example if they have an RPO of 5 minutes for critical systems within the management cluster in the event of a site failure this cannot be achieved via SRM with vSphere replication. For the conceptual design my example isn’t applicable but knowing this kind of limitation will then mean you know conceptually what needs to be created (multiple sites with fast links that have near zero latency for multiple data service providers and storage that can achieve this)

Given customer requirements and VMware technologies, determine availability impact to the conceptual design.

  • I feel this is largely what i have mentioned above but now you are including VMware technologies limitations/capabilities into your thinking which I actually did above. You will need to know what is and isn’t possible with HA for example and how it’s can only provide a certain level of availability and is limited by the amount of restarts it can achieve at once whilst being possibly limited by priority groups.

If you feel I have covered something incorrectly please let me know as I’m learning like everyone else and I certainly don’t claim to be perfect (near it but not perfect Winking smile ). Also the vBrownbag covered the whole of objective 1 here.

Gregg

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