In Docker, what's the difference between a container and an image? [duplicate]

Answer 1

An image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime. Images are read-only.

• https://docs.docker.com/glossary/?term=image

A container is an active (or inactive if exited) stateful instantiation of an image.

• https://docs.docker.com/glossary/?term=container

Answer 2

In easy words.

Images -

The file system and configuration(read-only) application which is used to create containers. More detail.

Containers -

These are running instances of Docker images. Containers run the actual applications. A container includes an application and all of its dependencies. It shares the kernel with other containers and runs as an isolated process in user space on the host OS. More detail.

---

Other important terms to notice:

---

Docker daemon -

The background service running on the host that manages the building, running and distributing Docker containers.

Docker client -

The command line tool that allows the user to interact with the Docker daemon.

Docker Store -

Store is, among other things, a registry of Docker images. You can think of the registry as a directory of all available Docker images.

A picture is worth a thousand words.

(For deeper understanding please read this.)

Summary:

• Pull image from Docker hub or build from a Dockerfile => Gives a Docker image (not editable).
• Run the image (docker run image_name:tag_name) => Gives a running Image i.e. container (editable)

Answer 3

Docker Images: It contains a list of commands and instruction on how to build and run a container. So basically Images contains all the data and metadata required to fire up a container(also called blueprint).We can't lunch a container without specifying Images.

$docker images centos

List all the available version of centos.

Docker Container: Containers are lunch from Images so we can say container is the running instance of an Images. Container is a runtime construct, unlike Images which is build time construct.

Answer 4

DockerFile --(Build)--> DockerImage --(run)--> DockerContainer

DockerFile is what you or developer write code to do something (ex- Install)

Docker Image is you get when you build docker file .

Docker Container is you get when you run your Docker image

We can get Docker Image from docker hub by pulling and then run it to get container .

Answer 5

Containers are based on images. An image needs to be passed to the Dockers run command.

Example:

BusyBox image

http://i.stack.imgur.com/eK9dC.png

Here we specify an image called busybox. Docker does not have this image locally and pulls it from a public registry.

A registry is a catalog of Docker images that the Docker client can communicate with and download image from. Once the image is pulled, Docker starts a container and execute the echo hello world command.

Answer 6

Using an object-oriented programming analogy, the difference between a Docker image and a Docker container is the same as that of the difference between a class and an object. An object is the runtime instance of a class. Similarly, a container is the runtime instance of an image.

An object gets created only once when it is instantiated. Similarly, a container can be running or stopped. Containers are created out of an image, though this might not always be the case. The following example creates an Apache server image, runs the image, lists the images and then lists the containers:

1. Create a Dockerfile with the following contents:

   FROM httpd:2.4
   

2. Install Apache server

   sudo docker build -t my-apache2 .
   

3. Run the image

   sudo docker run -it --rm --name my-running-app my-apache2
   

4. List Docker images

   sudo docker images
   

5. List the running Docker containers

   docker ps
   

6. List all containers

   docker ps -a
   

7. List latest created containers

   docker ps -l