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Although it's clear that DevOps and Agile are not the same thing, how exactly they differ may not be entirely apparent. But before we dive any deeper into the DevOps vs. Agile issue, what's perhaps most important to note is that while DevOps is the hot new paradigm, it doesn't mean that Agile is becoming a thing of the past, or that it doesn't have a role in DevOps. If anything, it's a big part of what DevOps is all about.
On a zoomed-out level, Agile is all about how you're developing software, while DevOps includes software development, while also focusing on how you can deploy and manage that software. More specifically, Agile has a tendency to only take things as far as staging, due to the lack of integration between developers and the operations team in non-DevOps environments. Once the Agile pipeline reaches its end, the operations folks take over and “never the twain shall meet.”
Not so in DevOps. The key, however, is that the two teams use processes to cut down bottlenecks, including operations' traditional testing/deployment/management, and bridge the gap that previously existed between them. Collaboration is the name of the game in DevOps, because increased communications between both sides is, ostensibly, the best way to improve both release cycles and the quality of the end product.
In short, Agile is different from DevOps insofar as the former is part of the latter. DevOps vs. Agile is not defined by opposition. Rather than being replaced by DevOps, Agile is supported by it – which can't be said for other approaches like the waterfall method. If the hallmarks of Agile are small and iterative software changes in response to shifting needs, then the DevOps principles of automation and collaboration in identifying and removing bottlenecks only help to get the changes out to users before the changes shift again.
Agile is still valuable and relevant, as it can be incorporated into DevOps and used to quickly put ideas to code and build them up, while the rest of the DevOps paradigm can be used to optimize the release and management of that product.