Docker for Rails Developers

Naming and Versioning Our Image

When we ran our Rails server with this command:

$ docker run -p 3000:3000 a1df0eddba18 \
    bin/rails s -b 0.0.0.0

we referred to our custom image by its ID: a1df0eddba18 (yours will differ). There’s no way we’re going to remember that. Just like you wouldn’t refer to a Git branch using the SHA-1 hash of its latest commit, the same is true for images. Instead, we give our images human-friendly names by tagging them. Let’s say we want to name our image railsapp. We can do this by running:

$ docker tag a1df0eddba18 railsapp

which says, “Tag the image identified by ‘a1df0eddba18’ with ‘railsapp’.” To verify this worked, let’s list our images with:

$ docker ...