Docker continuous deployment workflow

Question

I'm planning to set up a jenkins-based CD workflow with Docker at the end. My idea is to automatically build (by Jenkins) a docker image for every green build, then deploy that image either by jenkins or by 'hand' (I'm not yet sure whether I want to automatically run each green build).

Getting to the point of having a new image built is easy. My question is about the deployment itself. What's the best practice to 'reload' or 'restart' a running docker container? Suppose the image changed for the container, how do I gracefully reload it while having a service running inside? Do I need to do the traditional dance with multiple running containers and load balancing or is there a 'dockery' way?

Answer 1

Suppose the image changed for the container, how do I gracefully reload it while having a service running inside?

You don't want this.

Docker is a simple system for managing apps and their dependencies. It's simple and robust because ALL dependencies of an application are bundled with it. If your app runs today on your laptop, it will run tomorrow on your server. This is because we have captured 100% of the "inputs" for your application.

As soon as you introduce concepts like "upgrade" and "restart", your application can (accidentally) store state internally. That means it might behave differently tomorrow than it does today (after being restarted and upgraded 100 times).

It's better use a load balancer (or similar) to transition between your versions than to try and muck with the philosophy of Docker.