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Challenge - Volume

Run a database with a volume for persistent data.

Challenge: a safe update with a volume

To move a database image to a new version, the container is removed and recreated with the same volume. But a backup is taken first; if something goes wrong you go back to the backup:

# 1. backup
docker run --rm -v pgdata:/veri:ro -v "$PWD":/yedek alpine tar czf /yedek/pgdata.tar.gz -C /veri .
# 2. replace
docker rm -f db
docker run -d --name db -e POSTGRES_PASSWORD=gizli -v pgdata:/var/lib/postgresql/data postgres:16.4
# 3. check
docker logs --tail 5 db

Practice Back up

Write the command that, in an alpine container deleted when done, mounts pgdata read-only at /veri and the current folder ("$PWD") at /yedek, and runs tar czf /yedek/pgdata.tar.gz -C /veri .; then show the created file with ls -lh pgdata.tar.gz.

Starter code

terminal
# buraya yaz

Sample solution

terminal
docker run --rm -v pgdata:/veri:ro -v "$PWD":/yedek alpine tar czf /yedek/pgdata.tar.gz -C /veri .
ls -lh pgdata.tar.gz

Expected output

-rw-r--r-- 1 root root 6.1M Nov  3 11:42 pgdata.tar.gz

Practice Upgrade the version

Write three commands: force-remove the db container; start a container named db from postgres:16.4 in the background with POSTGRES_PASSWORD=gizli and the pgdata volume mounted at /var/lib/postgresql/data; show the last 5 log lines.

Starter code

terminal
# buraya yaz

Sample solution

terminal
docker rm -f db
docker run -d --name db -e POSTGRES_PASSWORD=gizli -v pgdata:/var/lib/postgresql/data postgres:16.4
docker logs --tail 5 db

Expected output

db
8f90a1b2c3d4
PostgreSQL Database directory appears to contain a database; Skipping initialization
LOG:  database system is ready to accept connections

Questions and answers

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

1 When the new container mounts the same pgdata volume, what happens if POSTGRES_PASSWORD is changed?

  • Nothing; the variable is only used for first setup on an empty data directory Correct answer
  • The password is updated
  • The data is deleted
  • The container doesn't start

Explanation: In an existing database, the password is changed with SQL (ALTER USER).

2 Extract the backup back into the volume.

Question 
docker run --rm -v pgdata:/veri -v "$PWD":/yedek alpine tar ____ /yedek/pgdata.tar.gz -C /veri
Answer 
docker run --rm -v pgdata:/veri -v "$PWD":/yedek alpine tar xzf /yedek/pgdata.tar.gz -C /veri

Explanation: x extracts, c creates.

3 Match.

Term Meaning
tar czf Take a backup
tar xzf Restore
docker rm -f db Remove the old container
postgres:16.4 New version

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