How do you back up and restore Docker volumes?

A common way to create a Docker volume is to use the dockervolumecreate command and specify the volume name. The steps include: 1. Create a named volume using dockervolume-createmy-volume; 2. Mount the volume to the container through dockerrun-vmy-volume:/path/in/container; 3. Verify the volume using dockervolumels and clean useless volumes with dockervolumeprune. In addition, anonymous volume or binding mount can be selected. The former automatically generates an ID by Docker, and the latter maps the host directory directly to the container. Note that volumes are only valid locally, and external storage solutions are required across nodes.

Docker containers are a lightweight, portable way to package applications and their dependencies together to ensure applications run consistently in different environments. Running instances created based on images enable developers to quickly start programs through "templates". Run the dockerrun command commonly used in containers. The specific steps include: 1. Install Docker; 2. Get or build a mirror; 3. Use the command to start the container. Containers share host kernels, are lighter and faster to boot than virtual machines. Beginners recommend starting with the official image, using dockerps to view the running status, using dockerlogs to view the logs, and regularly cleaning resources to optimize performance.

There are three common ways to set environment variables in a Docker container: use the -e flag, define ENV instructions in a Dockerfile, or manage them through DockerCompose. 1. Adding the -e flag when using dockerrun can directly pass variables, which is suitable for temporary testing or CI/CD integration; 2. Using ENV in Dockerfile to set default values, which is suitable for fixed variables that are not often changed, but is not suitable for distinguishing different environment configurations; 3. DockerCompose can define variables through environment blocks or .env files, which is more conducive to development collaboration and configuration separation, and supports variable replacement. Choose the right method according to project needs or use multiple methods in combination

To back up and restore Docker volumes, you need to use temporary containers in conjunction with tar tools. 1. During backup, run a temporary container that mounts the target volume, use the tar command to package the data and save it to the host; 2. During recovery, copy the backup file to the container that mounts the volume and decompress it, pay attention to path matching and possible overwriting of data; 3. Multiple volumes can be written to automatically cycle through each volume; 4. It is recommended to operate when the container is stopped to ensure data consistency, and regularly test the recovery process to verify the backup validity.

The main difference between Docker and traditional virtualization lies in the processing and resource usage of the operating system layer. 1. Docker containers share the host OS kernel, which is lighter, faster startup, and more resource efficiency; 2. Each instance of a traditional VM runs a full OS, occupying more space and resources; 3. The container usually starts in a few seconds, and the VM may take several minutes; 4. The container depends on namespace and cgroups to achieve isolation, while the VM obtains stronger isolation through hypervisor simulation hardware; 5. Docker has better portability, ensuring that applications run consistently in different environments, suitable for microservices and cloud environment deployment.

EXPOSE is used in Dockerfile to declare the network port the container will listen for at runtime, but it will not be published automatically to the host. Its core role is to provide documentation and configuration tips to help developers and tools understand the ports used by the application. To make the port accessible from the outside, you still need to use the -p parameter to map when running the container, for example: dockerrun-p8080:80my-web-app. The main reasons for using EXPOSE include improving clarity, supporting tool integration, and following best practices. Containers can directly access each other's exposed ports in the same custom network, but to access them on the host, the ports must be published explicitly. A common error is that you forget to map the port when running the container, causing the service to fail.

To view Docker container logs, use the dockerlogs command mainly. 1. Use dockerlogs [container name or ID] to view the log directly; 2. Add the -f parameter to track the log output in real time; 3. Use --timestamps or -t to display timestamps; 4. Use --since and --until to filter the logs by time range; 5. If the container has no shell, you can still access the stdout/stderr logs through dockerlogs, or mount the volume to access custom log files; 6. You can check the log driver used by the container through dockerinspect. If it is not the default JSON-file driver, you need to check the corresponding external system.

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