What is a Compose file?Ĭompose files are used in two types of deployments: in the non-cluster deployment with docker-compose and a cluster deployment with docker swarm. I'm not going to create a container from this image yet, that's for the next section. This will build an image tagged fortune:alpine. To build an image from this Dockerfile, using the docker CLI, run the following command docker build -t fortune:alpine. Since this isn't an article on container images, I'm going to refrain from over explaining that topic. An image is simply a template for the running containers, consisting of multiple read-only layers. from alpine:latestįrom this Dockerfile, you can now build a container image (or a docker image). The following is just as valid as the previous one. These instructions don't necessarily have to be written in capital letters. Take the example below: FROM alpine:latestĮach line starts with an instruction for the build component.
A typical Dockerfile contains special build instructions, commands like RUN, ADD, COPY, ENTRYPOINT, etc. I like to call Dockerfile the predecessor of a container image. Let me go in a bit of detail so that you properly understand the difference between Docker Compose and Dockerfile. It is easy to confuse the two terms, but it's also necessary to understand the difference when making a conversation with a colleague or your (potential) employer.ĭockerfile is what's used to create a container image, and a Compose file is what's used to deploy an instance of that image as a container. This is primarily because both are used to modify a Docker image in a way, though it's not technically correct. I've seen many people get confused between a Dockerfile and a Compose file.
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