A few days back, I got an
opportunity to present at vForum 2013 in Mumbai, the Financial Capital of
India. With more than 3000 participants across 2 days of this mega event, it
was definitely one of the biggest customer events in India. I along with my team was re-presenting the VMware Professional
Services at vForum and I was given the opportunity present on the following topic:-
"Architecting
vSphere Environments - Everything you wanted to know!"
When we finalized the topic, I
realized that the presenting this topic in 45 minutes is next to
impossible. With the amount of complexity which goes into Architecting a
vSphere Environment, one could actually write an entire book. However, the task on
hand was to narrate the same in form of a presentation.
As I started planning the slides, I
decided to look at the architectural decisions, which in my experience are
the "Most Important One's". These are important decisions as they can make
or break the Virtual Infrastructure. The other filtering criterion was to
ensure that I talk about the GREY AREAS where I always
see uncertainty. This uncertainty can transform a Good Design into a Bad design. At the end I was able to come out with a final presentation which
was received very well by the attendees. I thought of sharing the content with the entire community through this blog series and this being the Part 1, where I will give you some key design considerations for designing vSphere Clusters.
Before I begin, I would also want to give the credit
to a number of VMware experts in the community. Their books, blogs and the
discussions which I have had with them in the past, helped me in creating this
content. This includes books & blogs by Duncan, Frank, Forbes Guthrie, Scott
Lowe, Cormac Hogan &
some fantastic discussions with Michael
Webster earlier this year.
Here is a small Graphical Disclaimer:-
Here are my thoughts on creating vSphere Clusters!!
The message behind the
slide above is to create vSphere Clusters based on the purpose they need to
fulfill in the IT landscape of your organization.
Management
Cluster
The management cluster
refers here to a 2 to 3 host ESXi host which is used by the IT team to
primarily host all the workloads which are used to build up a vSphere
Infrastructure. This includes VMs such as vCenter Server, Database Server,
vCOps, SRM, vSphere Replication Appliance, VMA Appliance, Chargeback Manager
etc. This cluster can also host other infrastructure components such as Active
Directory, Backup Servers, Anti-virus etc. This approach has multiple benefits such
as:-
- Security due to isolation of management workloads from production workloads. This gives a complete control to the IT team on the workloads which are critical to manage the environment.
- Ease of upgrading the vSphere Environment and related components without impacting the production workloads.
- Ease of troubleshooting issues within these components since the resources such as compute, storage and network are isolated and dedicated for this cluster.
A quick tip would be to ensure that this cluster is minimum a
2 node cluster for vSphere HA to protect workloads in case one host goes down.
A three(3) node management cluster would be ideal since you would have the
option of running maintenance tasks on ESXi servers without having to disable
HA. You might want to consider using VSAN for this infrastructure as this
is the primary use case which both Rawlinson & Cormac suggest. Remember, VSAN
is in beta right now, so make your choices accordingly.
Production
Clusters
As the name suggests
this cluster would host all your production workloads. This cluster is the heart
of your organization as this hosts the business applications, databases, web
services, literally this is what gives you the job of being a VMware architect
or a Virtualization Admin. J
Here are a few
pointers which you need to keep in mind while creating Production Clusters:-
- The number of ESXi hosts in a cluster will impact you consolidation ratios in most of the cases. As a rule of thumb, you will always consider one ESXi host in a 4 node cluster for HA failover (assuming), but you could also do the same on a 8 node cluster, which ideally saves 1 ESXi host for you for running additional workloads. Yes, the HA calculations matter and they can be either on the basis of slot size or percentage of resources.
- Always consider at least 1 host as a failover limit per 8 to 10 ESXi servers. So in a 16 node cluster, do not stick with only 1 host for failover, look for at least taking this number to 2. This is to ensure that you cover the risk as much as possible by providing additional node for failover scenarios
- Setting up large clusters comes with their benefits such as higher consolidation ratios etc., they might have a downside as well if you do not have the enterprise class or rightly sized storage in your infrastructure. Remember, if a Datastore is presented to a 16 Node or a 32 Node cluster, and on top of that, if the VMs on that datastore are spread across the cluster, chances that you might get into contention for SCSI locking. If you are using VAAI this will be reduced by ATS, however try to start with small and grow gradually to see if your storage behavior is not being impacted.
· Having separate ESXI servers for DMZ workloads is OLD SCHOOL. This
was done to create physical boundaries between servers. This practice is a true
burden which is carried over from physical world to virtual. It’s time to shed
that load and make use of mature technologies such as VLANs to create logical
isolation zones between internal and external networks. In worst case, you
might want to use separate network cards and physical network fabric but you
can still run on the same ESXi server which gives you better consolidation ratios
and ensures the level of security which is required in an enterprise.
Island
Clusters
Yes they sound fancy but the concept of Island clusters
as laid down in my slides is to run islands of ESXi servers (small groups)
which can host workloads which have special license requirements. Although I do
not appreciate how some vendors try to apply illogical licensing policies on
their applications, middle-ware and databases, this is a great way of avoiding
all the hustle and bustle which is created by sales folks. Some of the examples
for Island Clusters would include
· Running Oracle Databases/Middleware/Applications on their
dedicated clusters. This will not only ensure that you are able to consolidate
more and more on a small cluster of ESXi hosts and save money but also ensure
that you ZIP the mouth of your friendly sales guy by being in what they think
is License Compliance.
· I have customers who have used island clusters of operating
systems such as Windows. This also helps you save on those datacenter,
enterprise or standard editions of Windows OS.
· Another important benefit of this approach is that it helps ESXi
use the memory management technique of Transparent Page Sharing (TPS) more
efficiently since with this approach there are chances that you are running a
lot of duplicate pages spawned by these VMs in the physical memory of your ESXi
servers. I have seen this going up-to 30 percent and this can be fetched in a
vCenter Operations Manager report if you have that installed in your Virtual
Infrastructure.
With this I would close this article. I was
hoping to give you a quick scoop in all these parts, but this article is now
four pages J. I hope this helps you
make the right choices for your virtual infrastructure when it comes to vSphere
Clusters.
Stay tuned for the other parts in the near
future…
As always – Share
& Spread the Knowledge!!