CentOS 7, cloud-init and DataSourceConfigDriveNet

Something I ran into when developing the novajoin service was that my cloud-init script was not executed if either force_config_drive was True in nova.conf or if config_drive was enabled for a particular instance. What I’d see is that no metadata would come across and cloud-init would do very little work at all beyond adding keypairs and configuring networking.

The image I was working on was CentOS-7-x86_64-GenericCloud.qcow2 (1511). If I used a similar RHEL 7 image things worked fine.

I determined the issue to be with the version of cloud-init. You need cloud-init-0.7.6 for config-drive to work. I got a copy of the cloud-init rpm that Red Hat uses and used virt-customize to update my CentOS image and things worked after that.

$ virt-customize -a CentOS-7-x86_64-GenericCloud.qcow2 --install

With this image the novajoin service can push a cloud-init script that will enroll the instance into IPA.

nova metadata REST API

The nova service includes a metadata server where information about an instance is made available to that instance (for use during cloud-init, for example). This includes common things like the hostname, root password, ssh keypairs, etc.

A relatively new feature in Newton adds dynamic providers. When a request is made for metadata nova will contact the configured providers using a REST API and include the returned values in the metadata.

To enable dynamic metadata, add “DynamicJSON” to the vendordata_providers configuration option. This can also include “StaticJSON”

The vendordata_dynamic_targets configuration option specifies the URLs to be retrieved when metadata is requested.tance.

The format for an entry in vendordata_dynamic_targets is: @

Name is a string to distinguish this dynamic metadata from other dynamic providers. This will used as the key to the metadata returned to the instance.

Where name is a short string not including the ‘@’ character, and where the
URL can include a port number if so required. An example would be::

For example: test@

This dynamic metadata is available in a new file, openstack/2016-10-06/vendor_data2.json

It can be retrieved as an URL from within an instance using:

$ curl

The output will look something like:

    "test": {
        "key1": "somedata",
        "key2": "something else",

The following is passed to the dynamic REST server when nova receives a metadata request:

project-idThe UUID of the project that owns this instance.
instance-idThe UUID of this instance.
image-idThe UUID of the image used to boot this instance.
user-dataAs specified by the user at boot time.
hostnameThe hostname of the instance.
metadataAs specified by the user at boot time (aka properties)