Ironic Python Agent is an agent for controlling and deploying Ironic controlled baremetal nodes. Typically run in a ramdisk, the agent exposes a REST API for provisioning servers.
Throughout the remainder of the document, Ironic Python Agent will be abbreviated to IPA.
IPA works with the agent Deploy driver in Ironic to provision nodes. Starting with ironic-python-agent running on a ramdisk on an unprovisioned node, Ironic makes API calls to ironic-python-agent to provision the machine. This allows for greater control and flexibility of the entire deployment process.
IPA may also be used with the original Ironic pxe driver as of the Kilo OpenStack Ironic release.
On startup, the agent performs a lookup in Ironic to determine its node UUID by sending a hardware profile to the Ironic vendor_passthru lookup endpoint: /v1/drivers/{driver}/vendor_passthru/lookup.
After successfully looking up its node, the agent heartbeats via /v1/nodes/{node_ident}/vendor_passthru/heartbeat every N seconds, where N is the Ironic conductor’s agent.heartbeat_timeout value multiplied by a number between .3 and .6.
For example, if your conductor’s ironic.conf contains:
[agent]
heartbeat_timeout = 60
IPA will heartbeat between every 20 and 36 seconds. This is to ensure jitter for any agents reconnecting after a network or API disruption.
After the agent heartbeats, the conductor performs any actions needed against the node, including querying status of an already run command. For example, initiating in-band cleaning tasks or deploying an image to the node.
IPA can conduct hardware inspection on start up and post data to the Ironic Inspector. Edit your default PXE/iPXE configuration or IPA options baked in the image, and set ipa-inspection-callback-url to the full endpoint of Ironic Inspector, for example:
ipa-inspection-callback-url=http://IP:5050/v1/continue
Make sure your DHCP environment is set to boot IPA by default.
IPA collects various hardware information using its Hardware Managers, and sends it to Ironic on lookup and to Ironic Inspector on Inspection.
The exact format of the inventory depends on the hardware manager used. Here is the basic format expected to be provided by all hardware managers. The inventory is a dictionary (JSON object), containing at least the following fields:
RAM information: total (total size in bytes), physical_mb (physically installed memory size in MiB, optional).
Note
The difference is that the latter includes the memory region reserved by the kernel and is always slightly bigger. It also matches what the Nova flavor would contain for this node and thus is used by the inspection process instead of total.
Unlike most other python software, you must build an IPA ramdisk image before use. This is because it’s not installed in an operating system, but instead is run from within a ramdisk.
One way to build a ramdisk image for IPA is with the CoreOS image [1]. Prebuilt copies of the CoreOS image, suitable for pxe, are available on tarballs.openstack.org.
On a high level, the build steps are as follows:
There are several methods you can use to customize the IPA ramdisk:
Another way to build a ramdisk image for IPA is by using diskimage-builder [3]. The ironic-agent diskimage-builder element builds the IPA ramdisk, which installs all the required packages and configures services as needed.
Additionally, the IPA ramdisk can be packaged inside of an ISO for use with supported virtual media drivers. Simply use the iso-image-create utility packaged with IPA, pass it an initrd and kernel. e.g.:
./iso-image-create -o /path/to/output.iso -i /path/to/ipa.initrd -k /path/to/ipa.kernel
This is a generic tool that can be used to combine any initrd and kernel into a suitable ISO for booting, and so should work against any IPA ramdisk created – both DIB and CoreOS.
You can pass a variety of flags to IPA on start up to change its behavior. If you’re using the CoreOS image, you can modify the ironic-python-agent.service unit in cloud-config.yaml [5].
Hardware managers are how IPA supports multiple different hardware platforms in the same agent. Any action performed on hardware can be overridden by deploying your own hardware manager.
Methods that modify hardware are dispatched to each hardware manager in priority order. When a method is dispatched, if a hardware manager does not have a method by that name or raises IncompatibleHardwareMethodError, IPA continues on to the next hardware manager. Any hardware manager that returns a result from the method call is considered a success and its return value passed on to whatever dispatched the method. If the method is unable to run successfully on any hardware managers, HardwareManagerMethodNotFound is raised.
IPA ships with GenericHardwareManager, which implements basic cleaning and deployment methods compatible with most hardware.
Custom hardware managers allow you to include hardware-specific tools, files and cleaning steps in the Ironic Python Agent. For example, you could include a BIOS flashing utility and BIOS file in a custom ramdisk. Your custom hardware manager could expose a cleaning step that calls the flashing utility and flashes the packaged BIOS version (or even download it from a tested web server).
Custom HardwareManagers should subclass hardware.HardwareManager or hardware.GenericHardwareManager. The only required method is evaluate_hardware_support(), which should return one of the enums in hardware.HardwareSupport. Hardware support determines which hardware manager is executed first for a given function (see: “How are methods executed on HardwareManagers?” for more info). Common methods you may want to implement are list_hardware_info(), to add additional hardware the GenericHardwareManager is unable to identify and erase_devices(), to erase devices in ways other than ATA secure erase or shredding.
One of the reasons to build a custom hardware manager is to expose extra steps in Ironic Cleaning [4]. A node will perform a set of cleaning steps any time the node is deleted by a tenant or moved from MANAGEABLE state to AVAILABLE state. If the node is using an agent_* driver, Ironic will query IPA for a list of clean steps that should be executed on the node. IPA will dispatch a call to get_clean_steps() on all available hardware managers and then return the combined list to Ironic.
To expose extra clean steps, the custom hardware manager should have a function named get_clean_steps() which returns a list of dictionaries. The dictionaries should be in the form:
{
// A function on the custom hardware manager
'step': 'upgrade_firmware',
// An integer priority. Largest priorities are executed first
'priority': 10,
// Should always be the deploy interface
'interface': 'deploy',
// Request the node to be rebooted out of band by Ironic when the
// step completes successfully
'reboot_requested': False
}
Then, you should create functions which match each of the step keys in the clean steps you return. The functions will take two parameters: node, a dictionary representation of the Ironic node, and ports, a list of dictionary representations of the Ironic ports attached to node.
When a clean step is executed in IPA, the step key will be sent to the hardware managers in hardware support order, using hardware.dispatch_to_managers(). For each hardware manager, if the manager has a function matching the step key, it will be executed. If the function returns a value (including None), that value is returned to Ironic and no further managers are called. If the function raises IncompatibleHardwareMethodError, the next manager will be called. If the function raises any other exception, the command will be considered failed, the command result’s error message will be set to the exception’s error message, and no further managers will be called. An example step:
def upgrade_firmware(self, node, ports):
if self._device_exists():
# Do the upgrade
return 'upgraded firmware'
else:
raise errors.IncompatibleHardwareMethodError()
Note
If two managers return steps with the same step key, the priority will be set to whichever manager has a higher hardware support level and then use the higher priority in the case of a tie.
Each hardware manager has a name and a version. This version is used during cleaning to ensure the same version of the agent is used to on a node through the entire process. If the version changes, cleaning is restarted from the beginning to ensure consistent cleaning operations and to make updating the agent in production simpler.
You can set the version of your hardware manager by creating a class variable named ‘HARDWARE_MANAGER_VERSION’, which should be a string. The default value is ‘1.0’. You should change this version string any time you update your hardware manager. You can also change the name your hardware manager presents by creating a class variable called HARDWARE_MANAGER_NAME, which is a string. The name defaults to the class name. Currently IPA only compares version as a string; any version change whatsoever will induce cleaning to restart.
A hardware manager has a single overall priority, which should be based on how well it supports a given piece of hardware. At load time, IPA executes evaluate_hardware_support() on each hardware manager. This method should return an int representing hardware manager priority, based on what it detects about the platform it’s running on. Suggested values are included in the HardwareSupport class. Returning a value of 0 aka HardwareSupport.NONE, will prevent the hardware manager from being used. IPA will never ship a hardware manager with a priority higher than 3, aka HardwareSupport.SERVICE_PROVIDER.
| [0] | Enabling Drivers - http://docs.openstack.org/developer/ironic/drivers/ipa.html#ipa |
| [1] | CoreOS PXE Images - https://coreos.com/docs/running-coreos/bare-metal/booting-with-pxe/ |
| [2] | (1, 2) CoreOS Cloud Init - https://coreos.com/docs/cluster-management/setup/cloudinit-cloud-config/ |
| [3] | DIB Element for IPA - http://docs.openstack.org/developer/diskimage-builder/elements/ironic-agent/README.html |
| [4] | Ironic Cleaning - http://docs.openstack.org/developer/ironic/deploy/cleaning.html |
| [5] | cloud-config.yaml - https://git.openstack.org/cgit/openstack/ironic-python-agent/tree/imagebuild/coreos/oem/cloud-config.yml |