How to check the port number in docker

Docker is a popular virtualization platform that allows developers to package applications into containers for easy deployment, management, and expansion. When using Docker to deploy applications, you often need to check the port number exposed by the container. This article will introduce how to view the port number exposed by the container in Docker.

What is a Docker container?

Docker container is a very important concept in Docker. It can be regarded as a lightweight independent running environment. Docker containers contain applications and dependent software libraries, as well as the operating system. Docker containers can be easily deployed and run on any platform, including operating systems such as Windows, Linux, and MacOS, making it an important tool for modern application deployment.

How to check the port number of a Docker container?

In a Docker container, the application will run in a virtual network. In order to make the application in the Docker container accessible from the outside, the port of the container needs to be exposed to the external network. There are two common port mapping methods for Docker containers: dynamic port mapping and static port mapping.

Dynamic port mapping

Dynamic port mapping means that Docker randomly selects an unused port and maps the container's port to this unused port. This method is particularly suitable for multi-container deployment scenarios.

When using dynamic port mapping in Docker, you can view the port information on which the container is running through the docker ps command. An example is as follows:

$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                     NAMES
9f41b43a95b3        nginx               "nginx -g 'daemon of…"   5 minutes ago       Up 5 minutes        0.0.0.0:32768->80/tcp     fervent_tesla

In the above output, you can see the container's ID, image, command, creation time, status and port mapping information, etc. Among them, the PORTS column shows the port mapping of the container. For example, in the output above, container port 80 has been mapped to port 32768 of the host.

Static port mapping

Static port mapping refers to mapping the port of the Docker container to a fixed port on the host network. This approach allows developers to more precisely control the port mapping relationship between the container and the host, thereby facilitating external access to the application.

When using static port mapping in Docker, you can use the docker ps command to view the port information on which the container is running. An example is as follows:

$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                               NAMES
9f41b43a95b3        nginx               "nginx -g 'daemon of…"   5 minutes ago       Up 5 minutes        0.0.0.0:80->80/tcp, 0.0.0.0:443->443/tcp   fervent_tesla

In the above example, the container's port 80 is mapped to the host's port 80, and the container's port 443 is mapped to the host's port 443. This means that when a user accesses port 80 or 443 of the host, they are actually accessing ports 80 and 443 of the container.

Conclusion

In Docker, port mapping is an important concept. Port mapping makes it easy to expose applications in containers to the external network. When using Docker to deploy an application, you need to pay attention to the port mapping method and mapped port number to ensure that the application can run normally. Through the introduction of this article, I hope readers can better understand port mapping in Docker, and then respond more flexibly to actual development and operation and maintenance work.

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