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Docker volume mounting and port mapping

Docker volume mounting and port mapping are two fundamental mechanisms for configuring container runtime behavior, specifically regarding data persistence and network accessibility.^[400-devops__06-Kubernetes__k8s-paas__01.Docker（已熟悉的可以从第二章开始）.md]

Volume Mounting

Volume mounting allows a user to connect a specific directory or file from the host machine to a path inside the container.^[400-devops__06-Kubernetes__k8s-paas__01.Docker（已熟悉的可以从第二章开始）.md]

This is primarily used for data persistence. Because containers are ephemeral, any data written inside a container's filesystem is lost when the container is removed. By mounting a volume, changes are written to the host machine, ensuring data is not lost if the container stops or is deleted^[400-devops__06-Kubernetes__k8s-paas__01.Docker（已熟悉的可以从第二章开始）.md]. Additionally, this technique is often used to inject configuration files into a container at runtime^[400-devops__06-Kubernetes__k8s-paas__01.Docker（已熟悉的可以从第二章开始）.md].

Usage

The syntax requires the -v (or --volume) flag followed by the host path and the container path separated by a colon^[400-devops__06-Kubernetes__k8s-paas__01.Docker（已熟悉的可以从第二章开始）.md].

Syntax: -v <host_directory>:<container_directory>

Example: To mount a local directory named html to the Nginx html directory: 

docker run -v /root/html:/usr/share/nginx/html ...
In this example, files in /root/html on the host will be visible inside the container at /usr/share/nginx/html^[400-devops__06-Kubernetes__k8s-paas__01.Docker（已熟悉的可以从第二章开始）.md].

Port Mapping

Port mapping creates a tunnel between a port on the host machine and a port inside the container^[400-devops__06-Kubernetes__k8s-paas__01.Docker（已熟悉的可以从第二章开始）.md]. This allows services running inside the container, which are isolated from the network by default, to be accessed via the host's IP address.

Usage

The operation uses the -p (publish) flag.^[400-devops__06-Kubernetes__k8s-paas__01.Docker（已熟悉的可以从第二章开始）.md]

Syntax: -p <host_port>:<container_port>

Example: To access a web server running on port 80 inside the container via port 81 on the host: 

docker run -p 81:80 ...
In this scenario, accessing localhost:81 on the host machine forwards the traffic to port 80 within the container^[400-devops__06-Kubernetes__k8s-paas__01.Docker（已熟悉的可以从第二章开始）.md].

Sources

^[400-devops__06-Kubernetes__k8s-paas__01.Docker（已熟悉的可以从第二章开始）.md]