Docker beginner

Difference between Dockerfile and Docker Compose

Dockerfile and Docker Compose are both important components of Docker, but they serve different purposes:

1. Dockerfile¹²³⁴⁵:
   • A Dockerfile is a text file that contains instructions for building a Docker image¹²³⁴⁵.
   • It’s essentially Docker’s version of a Makefile or build.gradle⁵.
   • It includes commands like RUN, ADD, COPY, ENTRYPOINT, etc².
   • You build an image from a Dockerfile².
   • An image is a template for running containers, consisting of multiple read-only layers².
   • Dockerfile is used to create a container image².
2. Docker Compose¹²³⁴⁵:
   • Docker Compose is a tool for defining and running multi-container Docker applications¹²³⁴⁵.
   • It uses a YAML file (docker-compose.yml) to define the services that make up your app so they can be run together in an isolated environment³.
   • A single Compose file can contain multiple container deployment configurations².
   • Docker Compose is used to deploy an instance of that image as a container².
   • It’s more readable, more maintainable, more intuitive².

In summary, a Dockerfile is used to build images, while Docker Compose is used to define and run multi-container applications¹²³⁴⁵. The Dockerfile uses the docker build command, while the docker-compose.yml file uses the docker-compose up command⁴. A docker-compose.yml file can reference a Dockerfile, but a Dockerfile can’t reference a docker-compose file⁴.

Specify docker image storage location

To specify a different storage location for Docker images, you need to modify Docker’s configuration. Here are the steps for Linux and Windows:

For Linux¹²:

1. Stop the Docker daemon if it’s running. You can do this with the command: sudo systemctl stop docker.
2. Create a daemon.json file in /etc/docker/ if it doesn’t exist¹.
3. Open the daemon.json file and add the following, replacing "/mnt" with your desired path¹:

{
  "data-root": "/mnt"
}

1. Save and close the file.
2. Start the Docker daemon with the command: sudo systemctl start docker.

For Windows³:

1. Quit Docker Desktop if it’s running.
2. Open the daemon.json file located at C:\ProgramData\Docker\config\.
3. Add the following to the file, replacing "D:\\Virtual Machines\\Docker" with your desired path³:

{
  "data-root": "D:\\Virtual Machines\\Docker"
}

1. Save and close the file.
2. Start Docker Desktop.

After making these changes, Docker will store its images in the specified directory. You can confirm the new storage location by running the command docker info and checking the Docker Root Dir value¹²³. Please note that you need to have the necessary permissions to read and write to the specified directory¹²³.

Docker remove container and image

# show all containers
docker ps -a

docker rm <container_id>
docker rmi <image_id>

Docker pull image with proxy

1. Create a systemd drop-in directory for the Docker service if it doesn’t exist²⁴:

mkdir /etc/systemd/system/docker.service.d

1. Create a file called /etc/systemd/system/docker.service.d/http-proxy.conf²⁴. Add the following content to the file, replacing proxy.example.com:80 with your proxy host and port²⁴:

[Service]
Environment="HTTP_PROXY=http://proxy.example.com:80/"
Environment="HTTPS_PROXY=http://proxy.example.com:80/"

If you have internal Docker registries that you need to contact without proxying, you can specify them via the NO_PROXY environment variable²:

Environment="NO_PROXY=localhost,127.0.0.0/8,docker-registry.somecorporation.com"

1. Reload the systemd daemon to apply the changes²⁴:

sudo systemctl daemon-reload

1. Restart the Docker service²⁴:

sudo systemctl restart docker

Now, Docker will use the specified proxy when pulling images²⁴.

Remember, you need to have the necessary permissions to create and modify files in /etc/systemd/system/docker.service.d²⁴. If you don’t, you may need to use sudo or log in as root²⁴. Also, ensure that your proxy server is properly configured and reachable from your Docker host²⁴.

Ubuntu repository mirror in China

http://ftp.sjtu.edu.cn/ubuntu/

Solve unable to connect to archive.ubuntu.com during docker build

Solution I tried but not work: https://gist.github.com/dyndna/12b2317b5fbade37e747

https://stackoverflow.com/questions/24991136/docker-build-could-not-resolve-archive-ubuntu-com-apt-get-fails-to-install-a

Tried replacing sources.list with tsinghua source list but not work.

Tried to pull the image and enter the conter to see if I can ping Failed.

docker run -it ubuntu bash

Tried solution in this doc https://talk.plesk.com/threads/docker-is-unable-to-connect-to-the-internet.370357/

Tried ping and curl on host machine ping does not work but curl can work. So I think I found the root cause. I set proxy for curl but I did not set proxy for ping.

And I should set proxy for container so that it can do apt-get update successfully. Add these lines to set proxy that is used in host machine for container.

# Update sources.list
RUN sed -i 's/http:\/\/archive.ubuntu.com\/ubuntu\//http:\/\/mirrors.tuna.tsinghua.edu.cn\/ubuntu\//g' /etc/apt/sources.list

ENV http_proxy http://28.10.10.62:8081
ENV https_proxy http://28.10.10.62:8081 

docker remove all containers

# show all containers
docker ps -a

docker rm $(docker ps -a -q -f status=exited)