Why docker local images are automatically cleared

As Docker becomes increasingly popular in the development and deployment fields, more and more people are looking for ways to maximize the benefits of its use. One of the questions is, why are local mirrors cleared automatically?

Docker is an open source platform that helps developers and operators build and deploy distributed applications more easily. One of the main features is the build image, which packages the application and all dependencies into a single file. Docker images can be built starting from a Docker base image or from other already built images. However, when the Docker image is stored locally, it is sometimes automatically cleared. Why is this?

One reason: space problem

One possible reason is space problem. When storing Docker images on the local host, the disk space of the system or other images must be taken into account. If there is insufficient disk space on the local storage device, Docker will automatically clear some images that are no longer needed.

This problem may occur on servers with insufficient disk space, or on machines where many images and containers have existed in the past. In this case, if you wish to save a specific image or container, you will need to back it up manually or move it to a larger storage device.

The second reason: garbage collection

Another reason is Docker’s garbage collection mechanism. This mechanism automatically cleans up images and containers that are no longer in use and deletes them from local storage. Docker garbage collection also cleans up any orphaned data volumes.

The main purpose of Docker garbage collection is to free up disk space and ensure that local storage is not overused. By default, this mechanism is triggered when disk usage exceeds 90%.

Solution

In order to avoid the problem of automatic clearing of Docker images, there are some solutions that can be adopted. First, you can regularly clean up images and containers that are no longer needed. If you know which images and containers you no longer need, manually deleting them is a good option.

Secondly, you can increase the disk space of your local storage device. This can be accomplished by adding a new hard drive or by upgrading an existing storage device.

Finally, you can disable Docker's garbage collection mechanism. This is not recommended because the purpose of garbage collection is to ensure that disk space is fully utilized. But if you want to have more control, you can adjust the triggering conditions for garbage collection or disable it entirely.

Conclusion

The automatic cleanup of the local Docker image may be caused by space problems or garbage collection mechanism. To avoid this problem, you can manually delete images and containers that are no longer needed, increase the disk space of the local storage device, or disable Docker's garbage collection mechanism. No matter which solution you choose, be sure to ensure long-term preservation and backup of your Docker images and containers.

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