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Automated OpenStack instance configuration with cloud-init and metadata service

Cloud Creator

Article from ADMIN 49/2019

By Grzegorz Juszczak

Today's OpenStack has become a mature product with automated asset configuration tools, including cloud-init, a powerful script that saves time by automatically configuring a large number of virtual servers in the cloud.

OpenStack has been constantly improved to meet the requirements of the demanding virtualization and cloud computing market. To challenge the competitive cloud solutions, OpenStack creators have been implementing a number of improvements and features in automation, orchestration, and scalability. Metadata services in cooperation with the cloud-init script deserve special attention.

The administration of large-scale production cloud environments requires the management of dozens of customer's virtual servers on a daily basis. Manual configuration of the multiple newly created instances in the OpenStack cloud would be a real pain for cloud administrators. Of course, you could use popular automation tools (e.g., Ansible, Chef, Puppet) to make a post-installation configuration on the virtual machines, but it still requires additional effort and resources to create the master server, templates, manifests, and playbooks and to build a host inventory or set up communication to virtual hosts. That's where the metadata and cloud-init duo comes in.

Metadata Service

The OpenStack metadata service usually runs on a controller node in a multinode environment and is accessible by the instances running on the compute nodes to let them retrieve instance-specific data (e.g., an IP address or hostname). Instances access the metadata service at http://169.254.169.254 . The HTTP request from an instance either hits the router or DHCP namespace, depending on the route in the instance. The metadata proxy service adds the instance IP address and router ID information to the request. The metadata proxy service then sends this request to the neutron-metadata-agent service, which forwards the request to the Nova metadata API service (nova-api-metadata server daemon) by adding some new headers (i.e., instance ID) to the request. The metadata service supports two sets of

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