DCA Question #3: Real Exam Question with Answer & Explanation

Question

Which of the following constitutes a production-ready devicemapper configuration for the Docker engine?

Options

• ACreate a volume group in devicemapper and utilize the '--dm.thinpooldev' Docker daemon option,
• BFormat a partition with xfs and mount it at '/var/lib/docker'
• CUtilize the '--storage-opt dm.directlvm_device' Docker daemon option, specifying a block device
• DNothing, devicemapper comes ready for production usage out of the box

Explanation

For a production-ready Devicemapper configuration, Docker should be configured to use a dedicated block device in direct-lvm mode.

Common mistakes.

• A. While --dm.thinpooldev specifies a thin pool, using dm.directlvm_device is the more automated and recommended production-ready approach for Devicemapper, managing the thin pool on a dedicated block device.
• B. Formatting a partition with XFS and mounting it at /var/lib/docker is a recommended setup for the overlay2 storage driver, not for the devicemapper driver which uses block devices directly or via LVM.
• D. The default loopback mode of Devicemapper is explicitly documented as suitable only for testing and development due to performance and stability limitations, not for production use.

Concept tested. Docker Devicemapper production configuration

Reference. https://docs.docker.com/engine/security/production-setup/#devicemapper

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