DevOps vs Docker

Question

I am wondering how exactly does docker fit into CI /CD . I understand that with help of containers, you may focus on code , rather than dependencies/environment. But once you check-in your code, you will expect tools like TeamCity, Jenkins or Bamboo to take care of integration build , integration test/unit tests and deployment to target servers ( after approvals) where you will expect same Docker container image to run the built code. However, in all above, Docker is nowhere in the CI/CD cycle , though it comes into play when execution happens at server. So, why do I see articles listing it as one of the things for DevOps. I could be wrong , as I am not a DevOps guru, please enlighten !

Answer 1

Docker is just another tool available to DevOps Engineers, DevOps practitioners, or whatever you want to call them. What Docker does is it encapsulates code and code dependencies in a single unit (a container) that can be run anywhere where the Docker engine is installed. Why is this useful? For multiple reasons; but in terms of CI/CD it can help Engineers separate Configuration from Code, decrease the amount of time spent doing dependency management etc., can use it to scale (with the help of some other tools of course). The list goes on.

For example: If I had a single code repository, in my build script I could pull in environment specific dependencies to create a Container that functionally behaves the same in each environment, as I'm building from the same source repository, but it can contain a set of environment specific certificates and configuration files etc.

Another example: If you have multiple build servers, you can create a bunch of utility Docker containers that can be used in your CI/CD Pipeline to do a certain operation by pulling down a Container to do something during a stage. The only dependency on your build server now becomes Docker Engine. And you can change, add, modify, these utility containers independent of any other operation performed by another utility container.

Having said all of that, there really is a great deal you can do to utilize Docker in your CI/CD Pipelines. I think an understanding of what Docker is, and what Docker can do is more important that a "how to use Docker in your CI/CD" guide. While there are some common patterns out there, it all comes down to the problem(s) you are trying to solve, and certain patterns may not apply to a certain use case.