Docker - Container and Image

Docker Container

Docker container is a running instance of an image. You can use Command Line Interface (CLI) commands to run, start, stop, move, or delete a container. You can also provide configuration for the network and environment variables. Docker container is an isolated and secure application platform, but it can share and access to resources running in a different host or container.

Docker Image

An image is a read-only template with instructions for creating a Docker container. A docker image is described in text file called a Dockerfile, which has a simple, well-defined syntax.

Example

You can understand container and image with the help of the following command:

$ docker run hello-world

The above command docker run hello-world has three parts:

docker: It is docker engine and used to run docker program. It tells to the operating system that you are running docker program.
run: This subcommand is used to create and run a docker container.
hello-world: It is a name of an image. You need to specify the name of an image which is to load into the container.

Special commands to use daily

Pulling Image:
```
$ docker pull nginx
```
- Used to pull an image from the docker hub and nginx is the name of the image.
Showing Image:
```
$ docker images ឬ $ docker image ls
```
- Used to show all images contained in the local machine.
Running Container:
```
$ docker run nginx:latest
```
- Used to run container, where nginx is the name of the image, and the latest is the version of the image and must be associated with a colon(:) in front of the version.
```
$ docker run -d nginx:latest
```
- Used to run the container same as docker run nginx:latest, but this command is executed in detached mode, that is, run the container and you can use the console where you are running the container normally, but if you use the above command, you cannot use the console.
Showing Container:
```
$ docker container ls ឬ $ docker ps
```
- Used to show all containers that are running.
```
$ docker ps -a
```
- Used to show all containers whether a container is running or stopped.
```
$ docker ps -q
```
- Used to show only the ID of the container that is running.
```
$ docker ps -aq ឬ $ docker ps -a -q
```
- Used to show only the ID of the container, for both running and stopped.
```
$ docker ps --format="ID\t{{.ID}}\nNAME\t{{.Names}}\nImage\t{{.Image}}\nPORTS\t{{.Ports}}\nCOMMAND\t{{.Command}}\nCREATED\t{{.CreatedAt}}\nSTATUS\t{{.Status}}\n"
```
- Used to show all containers that are running in easy-to-view format.
```
export FORMAT="ID\t{{.ID}}\nNAME\t{{.Names}}\nImage\t{{.Image}}\nPORTS\t{{.Ports}}\nCOMMAND\t{{.Command}}\nCREATED\t{{.CreatedAt}}\nSTATUS\t{{.Status}}\n"
```
- Used for export path variables in the machine for easy retrieval next time without having to write it more.
```
$ docker ps --format=$FORMAT
```
- Used to show a container that is formatted by calling the path variable.
Stop Container:
```
$ docker stop 19411e21c4fa
```
- Used to stop a container and 19411e21c4fais the container ID.
```
$ docker stop boring_merkle
```
- Used to stop the container same as in the above command, but docker stop 19411e21c4fa above use the container ID, but this command uses the name of the container, however you can use any options.
Exposing Port:
```
$ docker run -d -p 9000:80 nginx:latest
```
- Used to run the container in detached mode, and it includes with explicit specification with the expose port, which is used to run the nginx program, and to specify the expose port, and you need to use the -p flag, and then the port you want to place, and then the colon(:) and then the port of the container itself.
```
$ docker run -d -p 9000:80 -p 9010:80 nginx:latest
```
- Used to run the container same as in the above command, but for this command you can use multiple ports, ie port 9000 is successful or port 9010 is also successful.
Start Container:
```
$ docker start 19411e21c4fa ឬ $ docker start boring_merkle
```
- Used to start an existing container and you want to use the option start with the container ID or use the start option with the container name.
Removing Container:
```
$ docker rm 19411e21c4fa ឬ $ docker rm boring_merkle
```
- Used to remove the container, and this can be removed using the container ID or the container name, and you can remove the container only if the container is stopped.
```
$ docker rm -f 19411e21c4fa ឬ $ docker rm -f boring_merkle
```
- Used to remove the container same as in the above command, but this is in force mode, which means removing the container without having to stop the container, and you can remove it using the container ID or container name.
```
$ docker rm $(docker ps -aq)
```
- Used to remove all containers, using the container ID for all stopped containers.
```
$ docker rm -f $(docker ps -aq)
```
- Used to remove all containers, but you can delete both containers that running and not running.
Naming Container:
```
$ docker run -d --name nginx-ms -p 9000:80 nginx:latest
```
- Used to assign a name to what you want to name using --name flag, while nginx-ms is the container name.
Volumes:
```
$ docker run --name cambodia-website -d -p 9000:80 -v /home/mengsreang/Desktop/cambodia-website:/usr/share/nginx/html nginx:latest
```
- Used to run a container with specific volumnes that connect the project contained in your computer to the nginx server in the docker. A little simplification: The -v flag represents volumnes, while /home/mengsreang/Desktop/cambodia-website is your project location on the computer, and /usr/share/nginx/html is the project location of the nginx server. And don't forget to put a colon(:) in front of it.
```
$ docker exec -it cambodia-website bash
```
- Used to create a bash to access a project on nginx server. That exec command represents execute, while the -it flag means execute bash in interactive mode.

Docker - Container and Image