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Docker Configuration

Kismatic supports docker as the underlying container runtime for your cluster. During the installation of your cluster, Kismatic will download and install docker on all nodes.

Starting with KET v1.8.0 it is possible to use nodes with Docker already installed. When setting docker.disable to true KET will not try to install docker, and instead will validate that the docker command is available.

Storage in RHEL/CentOS (KET v1.3.1 - v1.7.1)

The default storage driver that gets installed on RHEL/CentOS is devicemapper in loop-lvm mode. However, this is not recommended for production setups. Instead, devicemapper must be setup in direct-lvm mode.

The direct-lvm mode requires a block storage device that will be used exclusively for docker's storage needs. For this reason, this is an opt-in feature that can be enabled in the plan file:

docker:
  storage:
    direct_lvm:                          # Configure devicemapper in direct-lvm mode (RHEL/CentOS only).
      enabled: false
      block_device: ""                   # Path to the block device that will be used for direct-lvm mode. This device will be wiped and used exclusively by docker.
      enable_deferred_deletion: false    # Set to true if you want to enable deferred deletion when using direct-lvm mode.

When direct-lvm is enabled, Kismatic will create a logical volume configured as a thin pool to use as the backing storage for docker. Creating a thin pool logical volume requires a "data" logical volume and a "metadata" logical volume.

The provided block storage device will be split 95% for data, and 1% for metadata, as recommended by Docker. The remaining space allows for auto-extending the logical volumes when they start to fill up as a temporary stop gap. The threshold for auto-extension is set to 80% of the size of the volume.

For more information on devicemapper see https://docs.docker.com/engine/userguide/storagedriver/device-mapper-driver/#configure-direct-lvm-mode-for-production

Storage (KET v1.8.0+)

Starting in KET v1.8.0 the docker storage options were modified to be more flexible. The old configuration will still work however it is recommended to start using the new format.

The new options docker.storage.driver and docker.storage.opts are equivalent to "storage-driver" and "storage-opts" in docker's daemon.json.

When docker.storage.driver is left empty, the docker daemon will determine the most suitable driver to use for the specific OS.

When setting docker.storage.driver to devicemapper, it is still possible for Kismatic to create the required storage device for direct-lvm mode. To do so, set docker.storage.direct_lvm_block_device.path to the absolute path of the block device. If the path is left empty with devicemapper driver, docker will be configured in loop-lvm.

docker:
  # Set to true if docker is already installed and configured.
  disable: false
  storage:
    # Leave empty to have docker automatically select the driver.
    driver: ""
    opts: {}
    # Used for setting up Device Mapper storage driver in direct-lvm mode.
    direct_lvm_block_device:
      # Absolute path to the block device that will be used for direct-lvm mode.
      # This device will be wiped and used exclusively by docker.
      path: ""
      thinpool_percent: "95"
      thinpool_metapercent: "1"
      thinpool_autoextend_threshold: "80"
      thinpool_autoextend_percent: "20"

Migrating to the new format

Old config (Deprecated)

docker:
  storage:
    direct_lvm:
      enabled: true
      block_device: "/dev/xvdb"

New Equivalent Config

docker:
  storage:
    driver: devicemapper
    opts:
      dm.thinpooldev: "/dev/mapper/docker-thinpool"
      dm.use_deferred_deletion: "false"
      dm.use_deferred_removal: "true"
    direct_lvm_block_device:
      path: "/dev/xvdb"
      thinpool_percent: "95"
      thinpool_metapercent: "1"
      thinpool_autoextend_threshold: "80"
      thinpool_autoextend_percent: "20"

Log Driver (KET v1.7.0+)

docker
  # Set to true if docker is already installed and configured.
  disable: false
  logs:
    driver: "json-file"
    opts:
      max-file: "1"
      max-size: "50m"

In the plan file the docker.logs field allows to set the docker daemon log driver options. The specified options from the plan file get set in /etc/docker/daemon.json.

This is an advanced feature and the values provided will not be validated, please refer to the documentation for your specific driver for the valid options.