Service Delivery: The Deployment Phase - The Practice of Cloud System Administration - page 219

• DNS: DNS translates names of machines to IP addresses. In an SDP, machines are
brought up and turned down rapidly. It is important to have the ability to update
DNS zones via an API or dynamic DNS (DynDNS/DDNS).
• Configuration Management Database (CMDB): The deployment phase should
be database driven. Configurations and machine relationships are stored in a data-
base, and the tools that build the environment use this information to guide their
work. This means modifying the environment is as simple as updating a database.
For example, the database might store the list of web server frontends associated
with a particular service. By adding to this list, the configuration management
tools will bring up web servers on those machines.
10.8 Summary
The deployment phase of the software delivery platform is where software packages are
turned into a running service. First the service is run in a testing environment. After an ap-
proval process is passed, the packages are used to build the live production environment.
Thedeploymentphaseinvolvesselectingagroupofpackagesthatrepresentalltheparts
of the service. Together they are considered a release candidate. They are installed on the
machinesthatmakeuptheenvironment.Theserviceisthenconfiguredandbecomesready
for testing or use.
Anenvironment requires infrastructure: hardware, network, and other components. Vir-
tual infrastructure can be configured through automation. Physical machines can also be
manipulated throughsoftware,althoughdoingsorequiresmoreplanningandisslowerand
less flexible. When infrastructure configuration is encoded in software, the entire infra-
structure can be treated as software, with all the benefits of source code: revision control,
testing, and so on.
Before a release is used in the live environment, it must pass many tests. System tests
check the system as a whole. Performance and load testing verify the software's perform-
ance.Useracceptancetestingisanopportunityforstakeholderstoapprovearelease.There
maybeotherapprovalssuchasthoseissuedbylegal,marketing,andproductmanagement.
Continuous delivery is achieved when the deployment phase and all testing is auto-
mated. New release candidates are produced automatically and confidence is improved as
the testing becomes more and more extensive.
Service delivery engineering is a large and changing field. We have only scratched the
surface in this chapter. We recommend the topic Continuous Delivery ( Humble & Farley
2010 ) for a deeper look at the subject.