If you do not have the right tools and processes in place, eventually you

end up with a broken production environment after shipping code. What is

one tool we can use to be confident that the code going into production is

not broken?

Automated testing, in its many forms, such as unit testing, integration

testing, security testing and performance testing, helps to ensure the

integrity of the code. You need to automate because manual testing is too

slow.

Other important tools that fall into the automated testing bucket but are

not traditionally thought of as a "test case" include code coverage and

code metrics (such as Cyclomatic Complexity).

Awesome, now you only deploy to production when a big batch of automated

test cases ensure the integrity of your code. All good, right?

Err, well no. Stuff can still break in production, espcially in environments

where for various reasons you do not have the same exact data in test

that you do in production. Your automated tests and code metrics will

simply not catch every last scenario that could go wrong in production.

When something goes wrong with your application, you need monitoring to

know what the problem is, and alerting to tell the right folks. Traditionally,

the "right" people were in operations. But over time many organizations

realized the ops folks ended up having to call the original application

developers who wrote the code that had the problem.

A critical piece to DevOps is about ensuring the appropriate developers

are carrying the pagers. It sucks to carry the pager and get woken up in the

middle of the night, but it's a heck of a lot easier to debug the code that

your team wrote than if you are a random ops person who's never seen the

code before in her life.

Another by-product of having application developers carry the "pagers" for

alerts on production issues is that over time the code they write is more

defensive. Errors are handled more appropriately, because otherwise you know

something will blow up on you later on at a less convenient time.