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9.2. Adding a config drive to all instances

As an administrator, you can configure the Compute service to always create a config drive for instances, and populate the config drive with metadata that is specific to your deployment. For example, you might use a config drive for the following reasons:

  • To pass a networking configuration when your deployment does not use DHCP to assign IP addresses to instances. You can pass the IP address configuration for the instance through the config drive, which the instance can mount and access before you configure the network settings for the instance.
  • To pass data to an instance that is not known to the user starting the instance, for example, a cryptographic token to be used to register the instance with Active Directory post boot.
  • To create a local cached disk read to manage the load of instance requests, which reduces the impact of instances accessing the metadata servers regularly to check in and build facts.

Any instance operating system that is capable of mounting an ISO 9660 or VFAT file system can use the config drive.

Procedure

  1. Open your Compute environment file.

  2. To always attach a config drive when launching an instance, set the following parameter to True: 

    parameter_defaults:
  ComputeExtraConfig:
    nova::compute::force_config_drive: 'true'

  3. Optional: To change the format of the config drive from the default value of iso9660 to vfat, add the config_drive_format parameter to your configuration: 

    parameter_defaults:
  ComputeExtraConfig:
    nova::compute::force_config_drive: 'true'
    nova::compute::config_drive_format: vfat
  4. Save the updates to your Compute environment file.

  5. Add your Compute environment file to the stack with your other environment files and deploy the overcloud: 

    (undercloud)$ openstack overcloud deploy --templates \
 -e [your environment files] \
 -e /home/stack/templates/<compute_environment_file>.yaml \

Verification

  1. Create an instance: 

    (overcloud)$ openstack server create --flavor m1.tiny \
 --image cirros test-config-drive-instance
  2. Log in to the instance.

  3. Mount the config drive:

    • If the instance OS uses udev: 

      # mkdir -p /mnt/config
# mount /dev/disk/by-label/config-2 /mnt/config

    • If the instance OS does not use udev, you need to first identify the block device that corresponds to the config drive: 

      # blkid -t LABEL="config-2" -odevice
/dev/vdb
# mkdir -p /mnt/config
# mount /dev/vdb /mnt/config
  4. Inspect the files in the mounted config drive directory, mnt/config/openstack/{version}/, for your metadata.