What is configuration drive (config-drive)?

Note! Please do not store data on config_drive.

Cloud-init
It is a tool used to perform initial setup on cloud nodes, including networking, SSH keys, timezone, user data injection, and more. It is a service that runs on the guest machine and supports Linux and Windows.

Metadata source
It is the source of configuration data for Cloud-init that typically come from the user (user_data) or come from the stack that creates the metadata ( configuration data). Typical userdata would include files, yaml, and shell scripts while typical metadata would include server name, instance id, display name and other cloud specific details.

Config-drive
It is another kind of configuration provider for Cloud-Init used by OpenStack. It  transfers some information to guest machine when guest machine is booting. 

Practically speaking, config-drive and Metadata source offer the same information.
The difference is:

• Config-drive doesn’t rely on network and directly gets information from a device, which causes better performance and low running cost.
• Metadata source is compatible with AWS (Amazon Cloud Service), but has less performance and higher running cost compared to config-drive.
  
  

Example 1: When DHCP is unavailable, guest machine can get network configuration from config_drive.

Example 2: When creating a complex guest machine

nova boot --config-drive=true --image my-image-name --key-name mykey --flavor 1 --user-data ./my-user-data.txt myinstance --file /etc/network/interfaces=/home/myuser/instance-interfaces --file known_hosts=/home/myuser/.ssh/known_hosts --meta role=webservers --meta essential=false

All the specific information can be retrieved from config_drive.

Note! Config-drive can only be specified when creating guest machine. Afterward, even though the configuration of guest machine is changed, the content of config-drive won’t change. 

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License
Changes were made based on the original Openstack User guide