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Build context

Learn what build context is and how it is used.

The build context

When docker build starts, it sends the whole context folder to the daemon. Files outside the context (like COPY ../gizli.txt .) can't be copied. A big context (e.g. node_modules, data files) slows the build:

$ docker build -t web .
[+] Building 12.4s
 => [internal] load build context
 => => transferring context: 845.21MB     # too big!

Choosing the context

The context and the Dockerfile location can be given separately. In a monorepo, making the root folder the context and using the Dockerfile in a subfolder is common:

# proje/
#   paylasilan/
#   servisler/api/Dockerfile
cd proje
docker build -f servisler/api/Dockerfile -t api .   # context: proje/

The context can also be a Git address: docker build https://github.com/ali/api.git#main.

Practice A monorepo build

You are inside the proje folder. Write the build command using servisler/api/Dockerfile, with the current folder as the context and the image name api:dev.

Starter code

terminal
# buraya yaz

Expected output

[+] Building 6.3s (10/10) FINISHED
 => naming to docker.io/library/api:dev done

Questions and answers

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

1 Why does COPY ../config.yml . fail?

  • COPY doesn't take single files
  • The file is outside the build context Correct answer
  • YAML isn't supported
  • The dot is wrong

Explanation: The daemon only sees the context sent to it.

2 Make the parent folder the context.

Question 
docker build -f Dockerfile -t api ____
Answer 
docker build -f Dockerfile -t api ..

Explanation: .. is the parent folder.

3 Match.

Term Meaning
context Folder sent to the daemon
-f Dockerfile location
transferring context Size sent
Git adresi Remote context

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