Comment 8 for bug 1652829

This issue can be explained by the way images used for VMs were configured:

1. Cloud-init was configured to use only Ec2 as its datasource, which means that on instance's boot all metadata was fetched from metadata-agent, even when config-drive was configured.
   ubuntu@wordpress-vm-0:~$ cat /etc/cloud/cloud.cfg.d/91-dib-cloud-init-datasources.cfg
   datasource_list: [ Ec2, None ]
2. At the same time, all instances were running an os-collect-config daemon that is constantly polling Neutron metadata agent and heat-api-cfn.

With several hundreds of simultaneous requests to handle metadata agent shows poor performance and can fail to serve requests within reasonable time (often taking over 10 seconds). These performance issues lead to some instances failing to get public keys on boot stage.

Note: Benchmarking of neutron metadata agent from a VM on a multinode DevStack and on CCP (both in default configuration) has shown significant performance drop on CCP:
DevStack http://paste.openstack.org/show/594838/
CCP http://paste.openstack.org/show/594839/

With images that are built to include ConfigDrive in a list of datasources this issue wasn't reproduced. Additionally it is possible to completely refrain from polling neutron metadata-agent using os-collect-config>=6.0.0b2.

I suggest to close this bug and open a new one concerning metadata-agent performance.