Another way to describe differences between Site Reliability Engineering and DevOps is to look at Wikipedia's explanation of a
Site Reliability Engineer, which starts like so:
Site reliability engineer (SRE) is a job description given to software engineers focused on reliability, scalability, and the development of cloud computing infrastructure, known as Site Reliability Engineering (SRE).
So you may consider SREs as people involved in
Building walls ...
However, Wikipedia's explanation of
DevOps starts like so:
DevOps ... is a term used to refer to a set of practices that emphasize the collaboration and communication of both software developers and information technology (IT) professionals while automating the process of software delivery and infrastructure changes. It aims at establishing a culture and environment where building, testing, and releasing software can happen rapidly, frequently, and more reliably.
What it doesn't say is that all these DevOps practices are actually triggered by a Demand from the business side. So combined with building and testing (the Develop part of it) and the Release of software, DevOps is about a DDR (= Demand-Develop-Release) culture and environment, which some people may remember from these 9 seconds of a historical speach to
Tear down this wall.
Refer to the question about Brief outage planned for Wed, May 3, 2017 at 8pm US/Eastern (like a fire drill for computers) for an example about all SE sites ... posted (signed) by a user with job title SRE Manager, Stack Overflow, Inc.