Service Delivery: The Deployment Phase - The Practice of Cloud System Administration - page 213

Every Step Has a Gate
The build process at StackExchange has a few different handoffs. Each is gated by
atestsothatdefectsaren'tpassedforward,tousetheassembly-lineanalogy.There
are many kinds of tests, each a separate module. The service delivery flow has the
following handoffs and gates:
1. Code is built and then packaging is gated by unit tests.
2. Digital signature verification gates whether the packager can pass code to the
test environment.
3. Promoting a release from the test environment to production is gated by sys-
tem tests.
4. Production environment upgrade success is gated by health checks.
10.2.2 Approval
If all the tests pass, the release is called a production candidate . Candidates are put
through an approval process. If they are approved they are installed in production.
At this point, the members of the approval chain are asked to sign off on the production
candidate. The approval chain is a list of specific people, or their delegates, who must sign
off on production releases. For example, the list might include the product manager, the
director of marketing, and the director of engineering. Often departmental approval is re-
quired from the security, legal, and privacy compliance departments.
Each environment may have a different set of tests and approval chain to gate which
releases may enter it. Deploying releases in the development and testing environments is
automatically approved. UAT and performance testing generally select the latest release
that has passed system testing. Environments that will have live users, such as beta and
demo environments, may be automatically upgraded periodically. For example, it is com-
mon for demo environments to be wiped and reloaded on a specific day of the week or a
certain duration before the official release date.
Environments that will be exposed to live, or revenue-generating, customers should be
gated with the most scrutiny. Thus the production environment generally requires all of the
preceding tests plus positive confirmation by the entire approval chain.