propose extra pre-provisioning kernel args

This commit:

- Introduces the proposal for BMH support for additional node specific kernel
  command line arguments for non dynamically built pre-provisioning images.

The motivation behind the commit can be found in the proposal.

Signed-off-by: Adam Rozman <adam.rozman@est.tech>

Author: Rozzii

design/baremetal-operator/node-specific-kernel-args.md

@@ -0,0 +1,186 @@
+<!--
+ This work is licensed under a Creative Commons Attribution 3.0
+ Unported License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+-->
+
+# pre-provisioning kernel argument support
+
+## Status
+
+planned
+
+## Summary
+
+This document proposes a new BareMetalHost spec attribute intended for
+configuring the pre-provisioning image's (usually IPA) kernel arguments.
+
+## Motivation
+
+There are situations where a user would need node specific kernel arguments
+for the pre-provisioning image. The reason could be the use of a mixed set of
+hardware, troubleshooting provisioning or boot issues, selectively configuring
+custom logic e.g. enabling IPA plugins or other services embedded in the
+pre-provisioning image.
+
+### Goals
+
+1. Implement a string type optional spec field named `preprovisioningExtraKernelParams`
+2. Extend the generic `Provisioner` interface to support the new optional field
+3. Implement support for the `preprovisioningExtraKernelParams` in the Ironic provisioner
+
+### Non-Goals
+
+1. To implement any sort validation for the new optional field
+2. Providing a default value for the new spec field
+3. Implement conditional logic to overwrite default kernel parameters on
+   per node basis
+
+## Proposal
+
+This document proposes a new BareMetalHost spec attribute intended for
+configuring the pre-provisioning image's (usually IPA) kernel arguments.
+
+The proposal involves the introduction of a new spec field thus a modification
+to the BMO API. The API change is intended to be backward compatible as the
+new `preprovisioningExtraKernelParams` field is optional.
+
+### Implementation Details/Notes/Constraints
+
+The `preprovisioningExtraKernelParams` field would be located directly under `spec`
+section. The format of the new field would be a list/array of individual
+strings. The new field would be optional and it would be considered
+either a NOOP or a cleaning operation depending on the previous value of the
+field in case it would be not present or have no value or would have an empty
+array as a value.
+
+The proposed BMH looks like the following:
+
+```yaml
+apiVersion: metal3.io/v1alpha1
+kind: BareMetalHost
+metadata:
+ name: bm0
+spec:
+ online: true
+ bmc:
+   address: idrac://192.168.122.1:6230/
+   credentialsName: bm0-bmc-secret
+ preprovisioningExtraKernelParams: "--timeout 60000 systemd.journald.forward_to_console=yes ipa-debug=1"
+   ...
+   ...
+   ...
+ bootMACAddress: 52:54:00:b7:b2:6f
+...
+...
+...
+
+```
+
+The example contains a snippet of a common IPA kernel argument list.
+The `preprovisioningExtraKernelParams` string would be received by the `Provisioner`
+interface as is. The handling of the list would be up to the particular
+implementations of the `Provisioner` interface.
+
+Given the BMH snippet from above, the kernel parameter list generated by
+the `Ironic provisioner` and posted to the Ironic Node API would look like
+almost the same with one important addition. The ironic provisioner will
+always prepend the `%default%` substring to the `preprovisioningExtraKernelParams`.
+
+The addition of the "%default%" will cause Ironic to inject the extra
+kernel parameters provided via the ironic config file and ironic-image
+environment variables. The inclusion of "%default%" is beneficial from
+multiple point of view, it makes the API based kernel parameter update logic
+consistent with the same feature used for dynamically built `preprovisioningImage`s.
+An other benefit is that kernel parameters coming from environment variables
+might contain credentials like ssh keys, or other sensitive information
+that would cause a security issue to display in a spec field.
+
+It is possible to implement an annotation or an other spec field to
+force BMO to overwrite the node specific kernel arguments. Implementing
+logic to conditionally overwrite the parameters might prove useful in some
+scenarios but it would completely deviate from how users are applying
+kernel parameters both with pre built or with dynamically build pre provisioning
+images thus using this feature might cause unexpected issues.
+
+In this proposal I am proposing the minimal viable feature to add node
+specific kernel arguments, in case in the future there will be interest in
+fully overwriting kernel parameters then the proposed feature can be extended
+with the relevant logic.
+
+### Risks and Mitigations
+
+Providing a faulty list kernel arguments might result in boot issues
+or unexpected behavior during the life cycle of the pre-provisioning image.
+
+The user has to be aware that the kernel arguments supplied here will fully or
+partially overwrite the default arguments depending on how the particular
+`Provisioner` is handling the argument list. In case of Ironic provisioner
+the `preprovisioningExtraKernelParams` will completely replace the default argument
+list used by Ironic.
+
+## Design Details
+
+Most of the design is very straightforward and easy to combine with the
+reconcile logic, the support for node specific pre-provisioning kernel args
+also already exist in Ironic, so right after the feature is implemented in BMO
+it can be used without waiting for Ironic implementation to arrive.
+
+The only challenge is the process of updating/cleaning the previously applied
+kernel argument list, this cleanup/update process highly depends on the
+particular provisioner.
+
+This document proposes extending the existing "NodeUpdate" functions of the
+Ironic provisioner utilized during provisioning, inspection and registration
+with updating the kernel parameters of the Ironic driver_info. In case of
+servicing and preparing states/operations "NodeUpdate"s have to be added this
+based on the user's workflow there might be a few extra node updates based on
+how many tines are the servicing or preparing logic is run.
+
+### Work Items
+
+- Implement a string type optional spec field named `preprovisioningExtraKernelParams`
+- Extend the generic `Provisioner` interface to support the new optional field
+- Implement support for the `preprovisioningExtraKernelParams` in the Ironic driver
+- Extend the data types used in different operational states to hold
+  an entry for `preprovisioningExtraKernelParams`
+- Implement unit tests, and align existing unit tests as needed
+- Add a check to the existing BMO e2e workflow that checks that the redfish
+  images and the PXE config files to verify that the provisioner image will
+  receive the correct parameters. Logging into a running IPA could also work
+  but in e2e tests Metal3 CI is using upstream IPA images that don't allow
+  users to log in via neither serial or ssh connections.
+
+### Dependencies
+
+- Ironic in case of the `Ironic Provisioner`
+
+### Test Plan
+
+- Unit tests for the functions
+- Integration testing with VMs, most likely as part of the existing
+  e2e workflow.
+
+### Upgrade / Downgrade Strategy
+
+- In case of upgrade user would not need to do anything
+- In case of downgrade the user has to remove the field from the BMH
+  to both make the BMH compatible with the older API and to allow the
+  particular provisioner in use to return using the defaults arguments list.
+
+### Version Skew Strategy
+
+None
+
+## Drawbacks
+
+None
+
+## Alternatives
+
+None
+
+## Reference
+
+None