9 docker commands for building and shipping images

Quick reference

Build and tag

# build from the Dockerfile here, with a tag
$docker build -t api:1.4.2 .
# add a second name, pointing at a registry
$docker tag api:1.4.2 registry.io/team/api:1.4.2
# rebuild from scratch when cache hides a change
$docker build --no-cache -t api:1.4.2 .

Push and pull

# authenticate to a private registry
$docker login registry.io
# upload the image
$docker push registry.io/team/api:1.4.2
# fetch it on the server
$docker pull registry.io/team/api:1.4.2

See inside, free space

# every layer and its size. Find the fat one
$docker history api:1.4.2
# the exact digest, for pinning
$docker image inspect api:1.4.2 --format '{{.Id}}'
# delete unused images. Reclaim the disk
$docker image prune -a

Explained

Build and tag

docker build -t api:1.4.2 . builds from the Dockerfile in the current directory and gives the image a name and tag. Always tag with a real version, never leave it as latest. docker tag api:1.4.2 registry.io/team/api:1.4.2 adds a second name pointing at your registry. The same image can carry several tags. docker build --no-cache forces a clean rebuild when a cached layer is hiding a change, like an apt package that updated upstream.

Push and pull

docker login authenticates to a private registry. docker push uploads the image and prints its digest, the content hash that identifies it exactly. docker pull fetches it on the target server.

Inspect and clean

docker history api:1.4.2 shows every layer and its size. This is how you find the one bloated layer to optimise. docker image inspect --format '{{.Id}}' gives the exact digest, which you use to deploy by digest instead of a movable tag. docker image prune -a deletes images nothing is using. On a busy build server, images and build cache quietly eat the disk; this reclaims gigabytes.

The two habits that matter: tag deliberately so you always know what you shipped, and prune on a schedule so the disk does not fill. docker system df shows how much space images, containers and cache are using right now.

In one line

Try it

$docker image prune -a

Pin what you ship

$docker build -t api:1.4.2 . && docker push ...