Welcome to the fourth blog in the Cloud Native series! In the previous two blogs, we have learned the basic concepts and introductory practices of Docker images. This blog will take you in-depth understanding of Docker containers and explore how to use Docker containers to build, run and manage applications. Whether you are a novice or an experienced developer, through the practical guidance of this blog, you will be able to become more familiar with and master the use of Docker containers.
Table of contents
1. Review of the basic concepts of Docker containers
Before we start exploring the practice of Docker containers, let's briefly review the basic concepts of Docker containers. A Docker container is an instance created based on a Docker image, and it is an independent and isolated operating environment. Each container contains everything needed to run an application, including the file system, system tools, libraries, and configuration. The emergence of containerization technology makes the development, testing and deployment of applications more flexible and efficient.
1.1 Features of Docker container
- Isolation : Docker containers provide strong isolation. Each container is an isolated operating environment and does not affect each other.
- Lightweight : Compared with traditional virtual machines, Docker containers are lighter and start and stop faster.
- Portability : Docker containers can run on different hosts and environments, regardless of differences in the underlying operating systems.
- Easy to manage : Containers can be managed through the command line or the Docker client, such as starting, stopping, restarting, and deleting.
2. Create and start Docker container
The required command is mainly docker run.
For example, the following command outputs a "Hello World" and then terminates the container.
$ docker run ubuntu:18.04 /bin/echo 'Hello world'
# Hello world
3. Run in guard state
More often, it is necessary to let Docker run in the background instead of directly outputting the result of executing the command to the current host. At this point, it can be achieved by adding the -d parameter.
Here are two examples to illustrate.
If you run the container without the -d parameter.
$ docker run ubuntu:18.04 /bin/sh -c "while true; do echo hello world; sleep 1; done"
The container will print the output (STDOUT) to the host
if the container is run with the -d parameter.
$ docker run -d ubuntu:18.04 /bin/sh -c "while true; do echo hello world; sleep 1; done"
5e99da6aae33ffa34700f71eea4a356b5cf135ad37756cf3848b4eeae2e806a2
At this time, the container will run in the background and will not print the output (STDOUT) to the host (the output can be viewed with docker logs).
docker container logs [container ID or NAMES]
4. Terminate the container
You can use docker container stopto terminate a running container.
In addition, when the application specified in the Docker container terminates, the container is automatically terminated.
For example, for the container that only started one terminal in the previous chapter, when the user exits the terminal through the exit command or Ctrl+d, the created container will terminate immediately.
example:
docker container stop 2d893c6294df604c3fd8f0e25e6975c0328fa6c65dcd763dab162e11dc281cfd
Terminated containers can be seen with the docker container ls -a command. For example
$ docker container ls -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
ba267838cc1b ubuntu:18.04 "/bin/bash" 30 minutes ago Exited (0) About a minute ago trusting_newton
In addition, the docker container restart command will terminate a running container and then restart it.
5. Enter the container
Sometimes you need to enter the container for operations, including using the docker attach command or the docker exec command. It is recommended that you use the docker exec command, and the reason will be explained below.
5.1 attach command
$ docker run -dit ubuntu
243c32535da7d142fb0e6df616a3c3ada0b8ab417937c853a9e1c251f499f550
$ docker container ls
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
243c32535da7 ubuntu:latest "/bin/bash" 18 seconds ago Up 17 seconds nostalgic_hypatia
$ docker attach 243c
root@243c32535da7:/#
5.2 exec command
5.2.1 -i -t parameters
Multiple parameters can be followed by docker exec. Here we mainly explain the -i -t parameters.
When only the -i parameter is used, since no pseudo-terminal is allocated, the interface does not have the familiar Linux command prompt, but the command execution result can still be returned.
When the -i -t parameters are used together, you can see the familiar Linux command prompt.
$ docker exec -it 69d1 bash
root@69d137adef7a:/#
You can also come in directly when you just run the container
docker run -it ubuntu:latest /bin/bash
6. View container list
To see a list of running containers, you can use docker psthe command. This command will display information such as container ID, image name, creation time, and running status.
docker ps
If you need to see all containers including stopped ones, you can use docker ps -athe command.
It can also be viewed on the Docker client:
7. Export and import
7.1 Export container
If you want to export a local container, you can use the docker export command.
$ docker container ls -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
7691a813g370e ubuntu:17.04 "/bin/bash" 21 hours ago Exited (0) 11 hours ago test
$ docker export 7691a813g370e > ubuntu.tar
This will export the container snapshot to a local file.
7.2 Import container snapshot
You can use docker import to import from the container snapshot file as a mirror image, for example
$ cat ubuntu.tar | docker import - dev/ubuntu:v2.0
$ docker image ls
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
dev/ubuntu v2.0 9d37a608a97 About a hour ago 143.3 MB
7.3 Delete container
To delete a stopped container, use docker rmthe command, specifying the ID or name of the container.
docker rm <容器ID或名称>
Summarize
Through the practical guidance of this blog, we have a deep understanding of the creation, operation, interaction, management and data management of Docker containers. Docker containers provide a lightweight, isolated operating environment that makes application development and deployment more flexible and efficient. Whether you are a developer or an operator, by mastering the use of Docker containers, we can better build, run, and manage applications.
I hope this blog has played a good guiding role in your understanding and use of Docker containers. In the next blog, we will further explore more functions and application scenarios of Docker to help you better use cloud native technology to build and deploy applications. Continue to pay attention to our cloud native｜Docker series, which will take you into the wonderful world of cloud native!