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Tagging images

Learn to tag images with the -t flag.

Tagging images

A full image name has the form [registry/][user/]repository:tag. The tag usually shows the version. One build can get several tags:

docker build -t api:1.4.2 -t api:1.4 -t api:latest .
docker build -t ghcr.io/ali/api:1.4.2 .

Semantic versioning (major.minor.patch) is common: 1.4.2 is fixed, while 1.4 and latest are moving tags pointing at the latest patch.

A tag is a pointer

A tag is a name pointing at an image ID (content digest); the same image can have several tags. docker tag adds a new name, the image isn't copied:

$ docker tag api:1.4.2 ali/api:1.4.2
$ docker images
REPOSITORY   TAG     IMAGE ID       SIZE
api          1.4.2   4f1e2d3c4b5a   162MB
ali/api      1.4.2   4f1e2d3c4b5a   162MB    # same ID

Practice Multiple tags

Write the command that produces the tags api:2.0.1, api:2.0 and api:latest from the current folder with a single build.

Starter code

terminal
# buraya yaz

Expected output

[+] Building 0.4s (10/10) FINISHED
 => naming to docker.io/library/api:2.0.1 done
 => naming to docker.io/library/api:2.0 done
 => naming to docker.io/library/api:latest done

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Why is a fixed version tag used in production instead of latest?

  • latest can't be pulled
  • latest is only for Windows
  • latest may point at different images over time; rollback and reproduction get hard Correct answer
  • latest is slower

Explanation: Knowing which version runs is the first step of debugging.

2 Give an existing image a new name.

Question 
docker ____ api:1.4.2 ali/api:1.4.2
Answer 
docker tag api:1.4.2 ali/api:1.4.2

Explanation: docker tag source target.

3 Match.

Term Meaning
1.4.2 Fixed version
1.4 Moving minor version
ghcr.io/ Registry address
IMAGE ID Content ID

All lessons in Beginner

1 What is Docker?

  1. What is Docker?
  2. Containers and virtual machines
  3. Images and containers
  4. Docker architecture
  5. Use cases
  6. Summary - What is Docker

2 Installation and first commands

  1. Installing Docker
  2. docker version
  3. docker info
  4. The hello-world container
  5. Docker Desktop
  6. Summary - Installation

3 First container

  1. docker run basics
  2. Running in the background
  3. docker ps
  4. docker stop and rm
  5. docker logs
  6. Summary - First container

4 Dockerfile basics

  1. What is a Dockerfile?
  2. The FROM instruction
  3. The RUN instruction
  4. COPY and ADD
  5. CMD and ENTRYPOINT
  6. Summary - Dockerfile

5 Build and images

  1. docker build
  2. Tagging images
  3. Build context
  4. Layers and cache
  5. .dockerignore
  6. Summary - Build

6 docker run options

  1. Interactive mode
  2. Naming containers
  3. Restart policy
  4. Working directory
  5. Switching users
  6. Summary - docker run

7 Image management

  1. docker images
  2. docker rmi
  3. docker pull
  4. docker push
  5. docker tag
  6. Summary - Image management

8 Port mapping

  1. The port concept
  2. The -p flag
  3. Multiple ports
  4. Random ports
  5. IP binding
  6. Summary - Port mapping

9 Volumes and data

  1. Data persistence
  2. Named volumes
  3. The -v flag
  4. Bind mounts
  5. Volume management
  6. Summary - Volumes

10 Environment variables

  1. The -e flag
  2. The ENV instruction
  3. The ARG instruction
  4. env-file
  5. The WORKDIR instruction
  6. Summary - Environment

11 Project: docker-compose

  1. Compose design
  2. Service definition
  3. Database service
  4. Volume and network
  5. Putting it together - compose

12 Docker Hub and registry

  1. What is Docker Hub?
  2. docker login
  3. Searching images
  4. Official images
  5. Private registry
  6. Summary - Registry

13 Network basics

  1. Network drivers
  2. docker network ls
  3. Bridge network
  4. Container connectivity
  5. Publishing ports
  6. Summary - Network

14 Beginner final

  1. Challenge - Dockerfile
  2. Challenge - Build and run
  3. Challenge - Volume
  4. Challenge - Compose
  5. Challenge - Beginner project