Problem Description

When the disk space of a thin pool on a node is about to be used up, the following exceptions occasionally occur:

Files or directories fail to be created in the container, the file system in the container is read-only, the node is tainted disk-pressure, or the node is unavailable.

You can run the docker info command on the node to view the used and remaining thin pool space to locate the fault. The following figure is an example.

Possible Cause

When Docker device mapper is used, although you can configure the basesize parameter to limit the size of the /home directory of a single container (to 10 GB by default), all containers on the node still share the thin pool of the node for storage. They are not completely isolated. When the sum of the thin pool space used by certain containers reaches the upper limit, other containers cannot run properly.

In addition, after a file is deleted in the /home directory of the container, the thin pool space occupied by the file is not released immediately. Therefore, even if basesize is set to 10 GB, the thin pool space occupied by files keeps increasing until 10 GB when files are created in the container. The space released after file deletion will be reused only after a while. If the number of service containers on the node multiplied by basesize is greater than the thin pool space size of the node, there is a possibility that the thin pool space has been used up.

Solution

When the thin pool space of a node is used up, some services can be migrated to other nodes to quickly recover services. But you are advised to use the following solutions to resolve the root cause:

Solution 1:

Properly plan the service distribution and data plane disk space to avoid the scenario where the number of service containers multiplied by basesize is greater than the thin pool size of the node.

Solution 2:

Create and delete files in service containers in the local storage (such as emptyDir and hostPath) or cloud storage directory mounted to the container. Such files do not occupy the thin pool space.

Solution 3:

Use the OverlayFS storage mode. This mode is used in CentOS 7.6 and Ubuntu 18.04 nodes in CCE Turbo clusters and Ubuntu 18.04 nodes in CCE clusters by default. You can deploy services on these nodes to prevent the problem that the disk space occupied by files created or deleted in the container is not released immediately.