How do you deploy your services? A decade ago, the assumption was that you were deploying your application to each of a number of servers, and that you would update the software on each server as you released new versions.  But today, a growing number of organizations are making use of containers and virtual machines to deploy in a totally different way, using immutable servers that are deployed a single time. Why have so many companies started to adopt this model, what are the advantages, and (just as importantly) what are the disadvantages?  What considerations should you have in mind when you switch to a set of immutable containers? In this talk, John Willis describes the thinking behind immutability, and what you should keep in mind if and when you switch to that approach.