Selecting a Service Platform - The Practice of Cloud System Administration - page 63

This service is ideal when you need a small or medium amount of datacenter space.
Such datacenters tend to be well designed and well run. While it can take years to procure
spaceandbuildadatacenter,usingacolocationfacilitycangetyouupandrunningquickly.
Colocation is also useful when you need many small spaces. For example, a company
mightwanttohaveasinglerackofequipmentineachofadozencountriestoprovidebetter
access for its customers in those countries.
ISPs often extend their network into colocation provider spaces so that tenants can eas-
ily connect to them directly. Being directly connected to an ISP improves access time for
theISP'susers.Alternatively,colocationprovidersmayprovideinternetaccessasaservice
to tenants, often by blending connections from two or more ISPs. Tenants can take advant-
age of this capability rather than manage their own ISP connections and relationships.
3.5 Selection Strategies
There are many strategies one may use to choose between IaaS, PaaS, and SaaS. Here are
a few we have used:
• Default to Virtual: Use containers or virtual machines wherever possible, opting
for physical machines only when performance goals cannot be achieved any other
way. For example, physical machines are generally better at disk I/O and network
I/O. It is common to see a fully virtualized environment with the exception of a
particularly demanding database with high I/O requirements. A web load balancer
may also be a candidate for physical hardware because of the availability of high-
bandwidth network interface cards or the benefit of predictable performance
gained from dedicated network connections.
• Make a Cost-Based Decision: Select a public cloud solution or a private cloud
solution based on cost. Create a business plan that describes the total cost of a pro-
ject if it is done in-house, on a private infrastructure, versus using a public cloud
provider. Choose the option with the lower cost. For a multiyear project, it may be
less expensive to do it yourself. For a short-term project, a public cloud is probably
the cheaper option.
• Leverage Provider Expertise: Use the expertise of cloud providers in creating an
infrastructure so your employees can focus on the application. This strategy is es-
pecially appealing for small companies and startups. With only one or two deve-
lopers, it is difficult to imagine building large amounts of infrastructure when pub-
lic cloud services are available. Public clouds are generally run more profession-
ally than private clouds because of the dynamics of competing against other pro-
viders for customers. Of course, private clouds can be run professionally, but it is
difficult to do at a small scale, especially without a dedicated staff.