How to Create a Docker Container from an Image?

Creating a Docker container from an image means starting a running version of a Docker image. A Docker image is a small, standalone software package. It includes everything we need to run a software, like the code, runtime, libraries, and other things. When we create a Docker container from an image, we make a separate space where our applications can run without messing with other applications or the main system.

In this article, we will show you how to create a Docker container from an image. We will talk about what we need before using Docker. Then we will explain how to pull a Docker image from Docker Hub. We will also go through the steps to create a Docker container with the Docker run command. After that, we will cover how to manage our Docker containers after we create them. We will also see how to access and work with them easily. Here are the topics we will talk about:

  • Creating a Docker Container from an Image Step by Step
  • What Prerequisites Do You Need for Docker?
  • How to Pull a Docker Image from Docker Hub?
  • How to Create a Docker Container Using the Docker Run Command?
  • How to Manage Your Docker Containers After Creation?
  • How to Access and Interact with Your Docker Container?
  • Frequently Asked Questions

For more reading on Docker and its parts, you might like these articles: What is Docker and Why Should You Use It?, How to Install Docker on Different Operating Systems, and What is a Docker Container and How Does It Operate?.

What Prerequisites Do You Need for Docker?

To make a Docker container from an image, we need to have some things ready first:

  1. Operating System: Docker works on many operating systems like:

    • Linux (Ubuntu, CentOS, etc.)
    • macOS
    • Windows 10 (Pro or Enterprise)

  2. Docker Installation: We must install Docker on our system. We can follow the official guide to install Docker for different operating systems here.

  3. Hardware Requirements:

    • We need at least 4GB of RAM (8GB is better).
    • Our CPU should support virtualization (Intel VT-x or AMD-V).

  4. User Permissions: We need permission to run Docker commands. Usually, we run these commands as a root user or we can add our user to the Docker group:

    sudo usermod -aG docker $USER

    After we run this command, we should log out and log back in for the changes to work.

  5. Network Access: We need internet access to get images from Docker Hub or other Docker registries.

  6. Understanding of Command Line: It is important to know a bit about command-line interfaces (CLI) to work with Docker.

When we have these things ready, we can create a Docker container from an image easily. For more details about Docker images and how they work, check this article What Are Docker Images and How Do They Work?.

How to Pull a Docker Image from Docker Hub?

To pull a Docker image from Docker Hub, we use the docker pull command. We follow this with the name of the image. Docker Hub is where we can find Docker images. It helps us share and manage our images.

Steps to Pull a Docker Image

  1. Open your terminal or command prompt.

  2. Use the docker pull command. The way to do this is:

    docker pull <image_name>:<tag>
    • <image_name>: This is the name of the Docker image we want to pull.
    • <tag>: This is the version of the image. If we do not put a tag, Docker pulls the latest version by default.

Example

If we want to pull the latest version of the Nginx image, we can run:

docker pull nginx:latest

If we want a specific version, like version 1.19, we can run:

docker pull nginx:1.19

Verifying the Image

After we pull the image, we can check if it downloaded correctly by listing the images on our local machine:

docker images

This shows us a list of all Docker images we have, including the one we just pulled.

For more detail about Docker Hub and what it can do, we can look at the article on what is Docker Hub and how do you use it.

How to Create a Docker Container Using the Docker Run Command?

To make a Docker container from an image, we use the docker run command. This command makes a container and also starts it. The simple way to write it is:

docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

Common Options for docker run:

  • -d: Run container in the background.
  • -p: Link host ports to container ports (for example, -p 8080:80).
  • --name: Give a name to the container.
  • -e: Set environment values (like -e ENV_VAR=value).
  • -v: Connect volumes (like -v /host/path:/container/path).

Example Commands:

  1. Running a Basic Container:

    docker run ubuntu

  2. Running a Detached Container:

    docker run -d --name my-nginx nginx

  3. Mapping Ports:

    docker run -d -p 8080:80 --name my-nginx nginx

  4. Setting Environment Variables:

    docker run -d -e MY_ENV=value --name my-app my-image

  5. Mounting a Volume:

    docker run -d -v /host/data:/container/data --name my-data-container my-image

Accessing the Container:

To work with the container after it has started, we can use:

docker exec -it my-nginx /bin/bash

This command will open a Bash shell inside the running my-nginx container.

For more details on how Docker works with images and containers, we can check out what is a Docker container and how does it differ from a virtual machine.

How to Manage Your Docker Containers After Creation?

After we create a Docker container from an image, it is really important to manage it well. This helps us keep everything running smoothly. Here are some simple commands and tips for managing our Docker containers.

Listing Docker Containers

To see all running containers, we can use:

docker ps

If we want to see all containers, even the stopped ones, we use:

docker ps -a

Stopping a Docker Container

If we need to stop a running container, we can use this command with the container ID or name:

docker stop <container_id_or_name>

Starting a Docker Container

To start a container that is stopped, we use:

docker start <container_id_or_name>

Removing a Docker Container

Before we remove a container, we need to make sure it is stopped. Then we can use:

docker rm <container_id_or_name>

If we want to remove all stopped containers, we can run:

docker container prune

Viewing Container Logs

To see the logs for a specific container, we use:

docker logs <container_id_or_name>

Executing Commands Inside a Running Container

If we want to run a command inside a running container, we can do it like this:

docker exec -it <container_id_or_name> <command>

For example, to open a shell session, we use:

docker exec -it <container_id_or_name> /bin/bash

Updating Container Configuration

When we need to update a container’s configuration, we usually have to recreate it with the new settings. First, we stop and remove the old container. Then we create a new one with the updated settings.

Inspecting a Container

To get detailed information about a container, including its settings and state, we can use:

docker inspect <container_id_or_name>

Networking and Port Mapping

To see the ports linked to a container, we check the output of:

docker ps

If we need to expose a port when we create a container, we use the -p flag like this:

docker run -d -p <host_port>:<container_port> <image_name>

Managing Container Resources

We can limit the resources for a container using flags like --memory and --cpus:

docker run -d --memory="256m" --cpus="1" <image_name>

These commands and tips will help us manage our Docker containers well after we create them. If you want to learn more about Docker containers, you can check this article.

How to Access and Interact with Your Docker Container?

We can access and interact with our Docker container using the docker exec command. This command lets us run commands inside a container that is already running. Here is how we can do it:

  1. List Running Containers: First, we need to find the container we want to access. We do this by listing all running containers.

    docker ps

  2. Access the Container: Next, we use the docker exec command with the -it flags. These flags mean interactive and terminal. This opens a shell in our container. We must replace container_name_or_id with our container’s actual name or ID.

    docker exec -it container_name_or_id /bin/bash

    If our container has a different shell, like sh, we can change /bin/bash to that shell.

  3. Run Commands Inside the Container: After we are inside the container, we can run any command like we are on a normal Linux machine.

  4. Exit the Container Shell: To leave the interactive shell, we just type exit or press Ctrl + D.

  5. Using Docker Attach: If we want to attach our terminal to the main process of a container, we can use this command:

    docker attach container_name_or_id

    We should know that this may not work well if the application in the container does not handle input/output properly.

  6. Viewing Container Logs: To see the logs of our container, we use this command:

    docker logs container_name_or_id

This helps us to check the output of our application that is running inside the Docker container.

For more details about Docker containers and how to manage them, we can look at what is a Docker container and how does it differ from a virtual machine.

Frequently Asked Questions

1. What is the difference between a Docker image and a Docker container?

A Docker image is a small package that has everything we need to run software. This includes code, libraries, and other things. A Docker container is what we call a running Docker image. It gives us a separate space for our applications. If we want to know more, we can read our article on what is a Docker image and how is it different from a container.

2. How do I pull a Docker image from Docker Hub?

To pull a Docker image from Docker Hub, we use the docker pull command. We write the image name and tag after it. For example, to get the latest Ubuntu image, we run:

docker pull ubuntu:latest

This command will download the image to our computer. We can then create a Docker container from it later. For more details, we can check our article on how do you pull a Docker image from Docker Hub.

3. What prerequisites do I need to create a Docker container?

Before we create a Docker container, we must have Docker installed on our system. We should also know some basic command-line interface (CLI) commands. It helps to understand Docker images too. We need to pull or have an image ready to make a container. For help on installation, we can visit our article on how to install Docker on different operating systems.

4. How can I access my Docker container once it’s created?

To access a running Docker container, we use the docker exec command. This command lets us run commands inside the container. For example, to start a shell session in a container called “my_container”, we write:

docker exec -it my_container /bin/bash

This way, we can work with the container directly. For more tips, we can look at our article on how to access and interact with your Docker container.

5. How do I manage my Docker containers after creation?

To manage our Docker containers, we can use commands like docker ps to see running containers. We can use docker stop to stop a container and docker rm to remove a stopped container. These commands help us keep our containers organized. For more management tips, we should check our article on how to manage your Docker containers after creation.