Deployment with Docker

Breaking the cache

In the container we just wrote, we somewhat glanced over the line RUN apt-get update -q && apt-get install -qy iputils-ping since it requires a bit of a deeper discussion here. In most Linux distributions, packages rotate in versions all the time, but the listing of these indexes that tell us where to find these is baked into the original Docker image when it gets created (ubuntu:latest in this case). Before we can install a package, in most cases, our index files have been stale for too long (if they haven't been completely removed), so we need to update them. Splitting this && joined line into two separate ones would work for that first build:

RUN apt-get update -qRUN apt-get install -qy iputils-ping

But what happens ...