1. Intro
The reason for this post is simple. I use docker here and then and tend to forget some commands and then i might not be sure if i’ll want to store the data (read: create a volume with it) or not, hence writing this post.
It about the basics how to get a docker container running, about containrs and volumes to get me/you started.
2. Docker Basic Terminology
Before diving into Docker commands, it’s important to understand the terminology used in Docker.
Here are some key terms:
- Image: A pre-built package that contains all the dependencies and configurations needed to run an application.
- Container: An instance of an image that runs in isolation from the host system and other containers.
- Dockerfile: A text file that contains instructions to build an image.
- Registry: A storage location for Docker images, such as Docker Hub.
3. Install Docker
Things might change in the future, so check here on how to install docker on your platform.
4. Pull an image
To get started with Docker, you’ll need to pull an image from a registry. For example, to pull the official Ubuntu image, you can use the following command:
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docker pull ubuntu
For ARM architecture we’d use one of the following commands (we can use other image apart from ubuntu or version 20.04).
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docker pull arm64v8/ubuntu
docker pull arm64v8/ubuntu:20.04
We can list images using following command:
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docker image ls
5. Run a container
Once you have an image, you can use it to run a container. For example, to run a container from the Ubuntu image, use the following command (add --name handle if you want to add a name):
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docker run -it ubuntu bash
This will start a container and open a bash shell inside it. The -it flag tells Docker to run the container in interactive mode, and the bash command starts a bash shell.
If you want to persist data you might want to add volume but more on that below in “Start a container and mount the volume”
We can check running conainers using following command
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docker container ls
Perhaps you want to see exited containers as well and if so add -a handle to the command above.
If we want to exit interactive shell and want to preserve the dockers session we can use Ctrl+P followed by Ctrl+Q.
If we want to enter the same container we need to use its name, in my case the container ran as frosty_noyce…
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docker exec -it frosty_noyce bash
Docker can be STOPed using following command
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docker container stop <id>
… or STARTed
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docker container stop <id>
Remove container:
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docker container rm <id>
5.1 Modify a container:
In the container itself, you can modify a container by installing packages or editing files inside it.
For example, to install the nginx package in the container, use the following command:
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apt-get update
apt-get install nginx
6. Volumes - Saving Changes
There are few possibilities how to persist data from a newly created container.
6.1 Create an Image
Once you have made changes to a container, you can create a new image from it using the docker commit command. For example, to create a new image from the modified Ubuntu container, use the following command:
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docker commit <container-id> my-ubuntu-image
Replace <container-id> with the ID of the container you want to create an image from, and my-ubuntu-image with a name for the new image.
6.2 Create a Volume and save data to it
Docker volumes provide a way to store data outside of a container’s filesystem and make it available to multiple containers. This allows you to separate data and application code, and makes it easier to manage and backup your data.
Here’s an example of how to use Docker volumes:
6.2.1 Create a volume:
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docker volume create mydata
This will create a new volume named mydata.
6.2.2 Start a container and mount the volume
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docker run -it -v mydata:/app/data ubuntu bash
This will start a container from the ubuntu image, and mount the mydata volume at the /app/data directory inside the container.
Make some changes inside the container, like creating new files or modifying existing ones, and save them to the mounted volume.
6.2.3 Stop and remove the container:
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docker stop <container-id>
docker rm <container-id>
Replace
6.2.4 Start a new container and mount the same volume:
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docker run -it -v mydata:/app/data ubuntu bash
This will start a new container from the ubuntu image, and mount the mydata volume at the /app/data directory inside the container. The changes you made in the previous container should now be available in this new container.
Note that Docker volumes can also be used to mount data from the host system or from other containers. For more information, see the Docker documentation on volumes: https://docs.docker.com/storage/volumes/
6.3 Dockerfile
6.3.1 Create a new directory
Create a new directory for your project, and create a file named Dockerfile inside it.
6.3.2 Specify the base image
In the Dockerfile, specify the base image you want to use for your new image
For example, if you want to use Ubuntu as the base image, you can add the following line to the Dockerfile:
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FROM ubuntu:latest
6.3.3 Add any additional commands
Add any additional commands you want to run in the container to the Dockerfile. For example, if you want to install the nginx web server, you can add the following line to the Dockerfile:
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RUN apt-get update && apt-get install -y nginx
You can also specify environment variables, work directory, or add files to the container by adding ENV, WORKDIR, and COPY commands respectively.
6.3.4 Save the Dockerfile
Save the Dockerfile and navigate to the directory in your terminal.
6.3.5 Build the Docker image using the following command
Build the Docker image
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docker build -t my-image-name .
The -t option specifies a name for the image, and the . at the end specifies the location of the Dockerfile.
6.3.6 Start a new container
After building, you can start a new container from your custom image:
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docker run -it my-image-name bash
This will start a new container from the my-image-name image and run the bash command inside it.
Note: It’s important to keep your Dockerfile as simple and clean as possible, and to use best practices for building images. The Docker documentation provides many useful tips and best practices for Dockerfile creation: https://docs.docker.com/develop/develop-images/dockerfile_best-practices/
7. Outro
It’s impossible to cover all scenarios without writing very lenghty article, but hopefully the few commands helped you with your docker endeavours and if not, just google or try asking OpenGPT