In the above example, you'll observe that there are 2 FROM statements. ĬOPY -from=0 /go/src//alexellis/href-counter/app. RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o app. Here's an example of multi-stage builds from the docker website FROM golang:1.7.3 Multi-Stage builds allow you to build the program in one container image, and copy over only the artifacts required from the first container image to a target image, which is what is used to run your program. Each instruction in a Dockerfile adds a layer (and code) to the docker image. When building docker images, its a challenge keeping the size of the image down. Multi-Stage builds in Docker, is an effort in composing minimal images. Since v 17.05, Docker supports multi-stage build images. distroless container images come with NO package manager, shell and other programs that come with a typical OS container image, thereby not only reducing unnecessary code, but reducing attack surface with it. Distroless images allow you to package only your application and its dependencies in a container image and run the container with a really light footprint. This is when I found distroless from Google.

This directly correlates with the possibility of pwnage of said environment, with an attacker being to leverage existing exploits against the programs running in the OS. The more code you run in your application environment, the higher the chance of a vulnerability creeping into said environment. I think the logic behind this is pretty simple. Running an entire OS, just for this, was not only overkill from a performance perspective, but from a security perspective as well. My apps were typically just a Python or NodeJS app or single binary that I need running in a container. That's because I was running an entire OS image, with package managers, shells, myriad utils that were completely unnecessary for my applications. My Docker images were wayyy larger than they needed to be. However, one thing was common in both situations. Alpine was much lighter than an Ubuntu, but it was still a full-fledged Operating system image Alpine is essentially busybox with package manager. More recently, as the Docker community started using Alpine Linux to build minimal images, I started to use Alpine too. Early in my container adoption days, it was Ubuntu 14.04, which would typically result in massive images, that were nothing less than 1GB each. However, most containers I would typically build, were built off an operating system Docker base-image. Containers are incredibly convenient to package and run your applications, consistently, with all the necessary dependencies. If you're like me, you're probably using Containers to deploy and run applications.

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