Ironic Python Agent

Overview

Ironic Python Agent (also often called IPA or just agent) is a Python-based agent which handles ironic bare metal nodes in a variety of actions such as inspect, configure, clean and deploy images. IPA is distributed over nodes and runs, inside of a ramdisk, the process of booting this ramdisk on the node.

For more information see the ironic-python-agent documentation.

Drivers

Starting with the Kilo release all drivers (except for fake ones) are using IPA for deployment. There are two types of them, which can be distinguished by prefix:

• For drivers with pxe_ or iscsi_ prefix IPA exposes the root hard drive as an iSCSI share and calls back to the ironic conductor. The conductor mounts the share and copies an image there. It then signals back to IPA for post-installation actions like setting up a bootloader for local boot support.
• For drivers with agent_ prefix the conductor prepares a swift temporary URL for an image. IPA then handles the whole deployment process: downloading an image from swift, putting it on the machine and doing any post-deploy actions.

Which one to choose depends on your environment. iSCSI-based drivers put higher load on conductors, agent-based drivers currently require the whole image to fit in the node’s memory.

Requirements

Using IPA requires it to be present and configured on the deploy ramdisk, see Building or downloading a deploy ramdisk image for details.

Using proxies for image download in agent drivers

Overview

IPA supports using proxies while downloading the user image. For example, this could be used to speed up download by using caching proxy.

Steps to enable proxies

1. Configure the proxy server of your choice (for example Squid, Apache Traffic Server). This will probably require you to configure the proxy server to cache the content even if the requested URL contains a query, and to raise the maximum cached file size as images can be pretty big. If you have HTTPS enabled in swift (see swift deployment guide), it is possible to configure the proxy server to talk to swift via HTTPS to download the image, store it in the cache unencrypted and return it to the node via HTTPS again. Because the image will be stored unencrypted in the cache, this approach is recommended for images that do not contain sensitive information. Refer to your proxy server’s documentation to complete this step.
2. Set [glance]swift_temp_url_cache_enabled in the ironic conductor config file to True. The conductor will reuse the cached swift temporary URLs instead of generating new ones each time an image is requested, so that the proxy server does not create new cache entries for the same image, based on the query part of the URL (as it contains some query parameters that change each time it is regenerated).
3. Set [glance]swift_temp_url_expected_download_start_delay option in the ironic conductor config file to the value appropriate for your hardware. This is the delay (in seconds) from the time of the deploy request (when the swift temporary URL is generated) to when the URL is used for the image download. You can think of it as roughly the time needed for IPA ramdisk to startup and begin download. This value is used to check if the swift temporary URL duration is large enough to let the image download begin. Also if temporary URL caching is enabled this will determine if a cached entry will still be valid when the download starts. It is used only if [glance]swift_temp_url_cache_enabled is True.
4. Increase [glance]swift_temp_url_duration option in the ironic conductor config file, as only non-expired links to images will be returned from the swift temporary URLs cache. This means that if swift_temp_url_duration=1200 then after 20 minutes a new image will be cached by the proxy server as the query in its URL will change. The value of this option must be greater than or equal to [glance]swift_temp_url_expected_download_start_delay.
5. Add one or more of image_http_proxy, image_https_proxy, image_no_proxy to driver_info properties in each node that will use the proxy. Please refer to ironic driver-properties output of the agent_* driver you’re using for descriptions of these properties.

Advanced configuration

Out-of-band Vs. in-band power off on deploy

After deploying an image onto the node’s hard disk Ironic will reboot the machine into the new image. By default this power action happens in-band, meaning that the ironic-conductor will instruct the IPA ramdisk to power itself off.

Some hardware may have a problem with the default approach and would require Ironic to talk directly to the management controller to switch the power off and on again. In order to tell Ironic to do that you have to update the node’s driver_info field and set the deploy_forces_oob_reboot parameter with the value of True. For example, the below command sets this configuration in a specific node:

ironic node-update <UUID or name> add driver_info/deploy_forces_oob_reboot=True