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Summary - Environment

Combine ENV, ARG and -e to write a configurable image.

Summary: environment

In this group:

  • -e NAME=value gives a variable at run time; -e NAME takes it from the host.
  • ENV adds a permanent default to the image; -e overrides it.
  • ARG is valid only in the build; it's filled with --build-arg and before FROM can choose the base image.
  • --env-file loads many variables from a file; secret files aren't put in the repository.
  • WORKDIR is the directory for the following instructions; RUN cd isn't persistent.
docker build --build-arg SURUM=1.5.0 -t api:1.5.0 .
docker run -d --env-file app.env -e LOG_LEVEL=debug api:1.5.0

Practice Build and run settings

Write two commands: build api:1.5.0 from the current folder with the build argument SURUM=1.5.0; then start a container named api in the background with the app.env file and LOG_LEVEL=debug.

Starter code

terminal
# buraya yaz

Sample solution

terminal
docker build --build-arg SURUM=1.5.0 -t api:1.5.0 .
docker run -d --name api --env-file app.env -e LOG_LEVEL=debug api:1.5.0

Expected output

[+] Building 2.9s (8/8) FINISHED
 => naming to docker.io/library/api:1.5.0 done
b4c5d6e7f809

Questions and answers

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

1 What is done to also read a build argument's value in the running container?

  • Nothing; ARG stays automatically
  • -e ARG is written
  • It isn't possible
  • It is passed to ENV with ENV NAME=$NAME Correct answer

Explanation: ARG disappears after the build; ENV stays in the image.

2 Override the env file value with a command option.

Question 
docker run -d --env-file app.env ____ LOG_LEVEL=debug api:1.0
Answer 
docker run -d --env-file app.env -e LOG_LEVEL=debug api:1.0

Explanation: -e takes precedence over the value in --env-file.

3 Match.

Term Meaning
-e Run-time variable
ENV Image default
ARG Build variable
--env-file Load from file

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