Deploying a non-HA Kubernetes platform

Device Mapper is a kernel-based framework that underpins many advanced volume management technologies on Linux®. Docker’s devicemapper storage driver leverages the thin provisioning and snapshot capabilities of this framework for image and container management.

Production hosts using the devicemapper storage driver must use direct-lvm mode. This mode uses block devices to create the thin pool. This is faster than using loopback devices, uses system resources more efficiently, and block devices can grow as needed.

The following steps create a logical volume configured as a thin pool to use as backing for the storage pool. It assumes that you have a spare block device at /dev/xvdf.

1. Identify the block device you want to use.

   The device is located under /dev/ (for example, /dev/xvdf) and needs enough free space to store the images and container layers for the workloads that the host runs. A solid state drive is ideal.

2. Stop Docker by running the following command:

   sudo systemctl stop docker

3. Install the following packages:

   RHEL / CentOS: device-mapper-persistent-data, lvm2, and all dependencies

4. Create a physical volume on your block device from step 1, using the pvcreate command and substituting your device name for /dev/xvdf.
   Important: The next few steps are destructive, so be sure that you have specified the correct device.

   sudo pvcreate /dev/xvdf

5. Create a docker volume group on the same device, using the vgcreate command:

   vgcreate docker /dev/xvdf

6. Create two logical volumes named thinpool and thinpoolmeta using the lvcreate command.
   The last parameter specifies the amount of free space to allow for automatic expanding of the data or metadata if space runs low, as a temporary stop-gap. These are the recommended values.

   sudo lvcreate --wipesignatures y -n thinpool docker -l 95%VG
   sudo lvcreate --wipesignatures y -n thinpoolmeta docker -l 1%VG

7. Convert the volumes to a thin pool and a storage location for metadata for the thin pool, using the lvconvert command:

   sudo lvconvert -y \
   --zero n \
   -c 512K \
   --thinpool docker/thinpool \
   --poolmetadata docker/thinpoolmeta

8. Configure autoextension of thin pools using an lvm profile:

   sudo vi /etc/lvm/profile/docker-thinpool.profile

9. Specify thin_pool_autoextend_threshold and thin_pool_autoextend_percent values:
   • thin_pool_autoextend_threshold is the percentage of space used before lvm attempts to autoextend the available space (100 = disabled, not recommended).
   • thin_pool_autoextend_percent is the amount of space to add to the device when automatically extending (0 = disabled).

   The following example adds 20% more capacity when the disk usage reaches 80%:

   activation {
     thin_pool_autoextend_threshold=80
     thin_pool_autoextend_percent=20
   }

   Save the file.

10. Apply the lvm profile using the lvchange command:

    sudo lvchange --metadataprofile docker-thinpool docker/thinpool

11. Enable monitoring for logical volumes on your host:

    sudo lvs -o+seg_monitor

    Without this step, automatic extension does not occur even in the presence of the lvm profile.

12. If you have ever run Docker on this host before, or if the /var/lib/docker/ directory exists, move the directory so that Docker can use the new lvm pool to store the contents of image and containers:

    mkdir /var/lib/docker.bk
    mv /var/lib/docker/* /var/lib/docker.bk
    

    Note: If any of the following steps fail and you need to restore, you can remove /var/lib/docker and replace it with /var/lib/docker.bk.
13. Edit /etc/docker/daemon.json and configure the options needed for the devicemapper storage driver.
    If the file was previously empty, it should now contain the following contents:

    {
        "storage-driver": "devicemapper",
        "storage-opts": [
        "dm.thinpooldev=/dev/mapper/docker-thinpool",
        "dm.use_deferred_removal=true",
        "dm.use_deferred_deletion=true"
        ]
    }

14. Start Docker:
    • systemd:

      sudo systemctl start docker

    • service:

      sudo service docker start

15. Verify that Docker is using the new configuration using the docker info command.

    If Docker is configured correctly, the Data file and Metadata file are blank, and the pool name is docker-thinpool.

16. After you have verified that the configuration is correct, you can remove the /var/lib/docker.bk directory which contains the previous configuration:

    rm -rf /var/lib/docker.bk

To configure loop-lvm mode for a proof-of-concept deployment, complete the following steps:

1. Stop Docker by running the following command:

   sudo systemctl stop docker

2. Edit the /etc/docker/daemon.json file (if it does not exist, create it now).

   Add or append the following lines into the file:

   {
     "storage-driver": "devicemapper"
   }

3. Start Docker by running the following command:

   sudo systemctl start docker

4. Verify that the daemon is using the devicemapper storage driver by running the docker info command and looking for Storage Driver.