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Installer/MCO: store pointer ignition customizations in MachineConfig
This is an alternative to #467
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Steven Hardy
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enhancements/machine-config/custom-ignition-machineconfig.md
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| --- | ||
| title: Store user ignition customizations in MachineConfig | ||
| authors: | ||
| - "@hardys" | ||
| - "@celebdor" | ||
| reviewers: | ||
| - "@celebdor" | ||
| - "@cgwalters" | ||
| - "@crawford" | ||
| - "@kirankt" | ||
| - "@runcom" | ||
| - "@stbenjam" | ||
| - "@yuqi-zhang" | ||
| approvers: | ||
| - "@cgwalters" | ||
| - "@crawford" | ||
| - "@runcom" | ||
| - "@yuqi-zhang" | ||
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| creation-date: 2020-08-21 | ||
| last-updated: 2020-11-13 | ||
| status: implementable | ||
| --- | ||
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| # Store user ignition customizations in MachineConfig | ||
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| ## Release Signoff Checklist | ||
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| - [x] Enhancement is `implementable` | ||
| - [ ] Design details are appropriately documented from clear requirements | ||
| - [ ] Test plan is defined | ||
| - [ ] Graduation criteria for dev preview, tech preview, GA | ||
| - [ ] User-facing documentation is created in [openshift-docs](https://github.com/openshift/openshift-docs/) | ||
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| ## Summary | ||
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| This enhancement proposes changing the way installer ignition customizations | ||
| are stored, so that instead of storing the modified pointer ignition in a | ||
| Secret we include the user changes in a MachineConfig, such that the MCO | ||
| can manage it, and it is included in the MCO rendered config. | ||
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| ## Motivation | ||
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| The installer supports user [modification of the pointer ignition config](https://github.com/openshift/installer/blob/master/docs/user/customization.md#os-customization-unvalidated) it generates. While this interface is marked as unvalidated, we know from [previous bug reports](https://bugzilla.redhat.com/show_bug.cgi?id=1881703) that some users are using it. | ||
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| This presents a problem for the plans to have the [MCO manage the pointer config](https://github.com/openshift/enhancements/blob/master/enhancements/machine-config/user-data-secret-managed.md) | ||
| because it uses a static template that does not consider any user customizations, and for that reason the work was [reverted](https://github.com/openshift/machine-config-operator/pull/2126). | ||
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| Additionally, in some situations it is necessary to perform network configuration | ||
| before it is possible to download the rendered config from the MCS in the ramdisk | ||
| where ignition evaluates the pointer config. | ||
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| This leads to a chicken-egg problem, where a user could configure the network | ||
| via ignition, but ignition cannot apply any config until it has downloaded | ||
| any append/merge directives. | ||
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| We could solve that problem on some platforms (baremetal in particular) by | ||
| just providing the fully rendered config to each host, bypassing the pointer | ||
| config where config-drive size limits allow. However this results in the [same | ||
| issue with losing any user customizations](https://bugzilla.redhat.com/show_bug.cgi?id=1833483) provided directly via the pointer config. | ||
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| Discussions indicate we may want to deprecate/remove this ignition-config method of | ||
| customization and mandate MachineConfig manifests instead. We could in the | ||
| meantime do that internally e.g have the installer detect any customization | ||
| to the pointer config, and inject a MachineConfig manifest containing that data | ||
| instead of writing it via the current user-data Secret. | ||
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| ### Goals | ||
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| * Unblock the MCO managed pointer ignition work that was previously reverted | ||
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| * Provide a solution to customer requirements for baremetal IPI around bond/VLAN | ||
| and other configurations for controlplane networking | ||
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| * Provide a means by which we might warn the user if we decide to deprecate customization via the pointer ignition config. | ||
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| ### Non-Goals | ||
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| This work may give us some options wrt warnings around this interface but it | ||
| does not aim to formally deprecate the ignition-configs customization, that | ||
| may be separately discussed in a future enhancement. | ||
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| The discussion of interfaces here and how they relate to network configuration | ||
| only considers the existing interfaces, not proposals around a future | ||
| [declarative network configuration](https://github.com/openshift/enhancements/pull/399) although we need to ensure the approach taken in each case is aligned. | ||
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| ### User Stories | ||
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| #### Story 1 | ||
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| As a user I would like my existing customizations to pointer ignition files | ||
| to work, but be warned if there is a preferable interface I should be using. | ||
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| #### Story 2 | ||
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| As a baremetal IPI user, I need to deploy in an environment where network | ||
| configuration is required before access to the controlplane network is possible. | ||
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| Specifically I wish to deploy in an environment where the controlplane is | ||
| on a non-default VLAN (a common configuration for baremetal). | ||
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| Currently I cannot perform this configuration via ignition or MachineConfig, | ||
| because the pointer config requires network access prior to any configuration | ||
| being performed on the host. | ||
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| ## Design Details | ||
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| If the installer can detect the case where the pointer config loaded at `create cluster` contains | ||
| user customizations we can create a new MachineConfig object to encapsulate this config, | ||
| instead of persisting it to the user-data secret directly. | ||
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| This would be equivalent to the user creating those same customizations via a MachineConfig | ||
| manifests, and we could potentially warn users to guide them to that interface, | ||
| but avoid breaking any existing users performing customizations directly via | ||
| the pointer ignition. | ||
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| This would mean we can potentially restore the [MCO managed pointer ignition](openshift/machine-config-operator#1792) | ||
| work, where the MCO will maintain a templated pointer config, and any user customizations | ||
| will be persisted in the existing rendered config. | ||
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| This would also solve the issue for IPI baremetal without any [MCO API changes](https://github.com/openshift/enhancements/pull/467), since we could consume the existing rendered config directly. | ||
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| ### Test Plan | ||
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| * Ensure no regressions in existing deployments via existing e2e-metal-ipi CI coverage | ||
| * Prove we can do deployments where the controlplane network requires configuration, such as that described in [previous bug reports](https://bugzilla.redhat.com/show_bug.cgi?id=1824331) - we can add a periodic CI job based on e2e-metal-ipi to test this. | ||
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| ### Upgrade / Downgrade Strategy | ||
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| This change only impacts the day1 deployment, since the changes are in | ||
| the installer. | ||
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| If the MCO managed pointer ignition config work is restored, the upgrade | ||
| strategy will be defined in https://github.com/openshift/enhancements/blob/master/enhancements/machine-config/user-data-secret-managed.md | ||
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| ### Version Skew Strategy | ||
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| ## Alternatives | ||
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| ### Native ignition support for early-network config | ||
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| This was initially proposed via [an ignition issue](https://github.com/coreos/ignition/issues/979) | ||
| where we had some good discussion, but ultimately IIUC the idea of adding a new | ||
| interface for early network configuration to ignition was rejected. | ||
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| ### Implement MCO support for a flattened ignition config | ||
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| This was discussed in https://github.com/openshift/enhancements/pull/467 and | ||
| the solution documented here is derived from discussion on that PR. | ||
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| ### Implement config flattening in platform-specific repos | ||
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| The ignition configuration is consumed at two points during deployment for IPI baremetal | ||
| deployments: | ||
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| * Via terraform (when the installer deploys the controlplane | ||
| nodes using [terraform-provider-ironic](https://github.com/openshift-metal3/terraform-provider-ironic). | ||
| * Workers are then deployed via the machine-api, using a | ||
| [baremetal Cluster API Provider](https://github.com/openshift/cluster-api-provider-baremetal/) | ||
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| The ironic terraform provider is designed to be generic, and thus we would prefer | ||
| not to add OS specific handling of the user-data there, and in addition [previous | ||
| prototying of a new provider](https://github.com/openshift-metal3/terraform-provider-openshift) | ||
| indicates that due to terraform limitations it is not possible to | ||
| pass the data between providers/resources in the way that would be required. | ||
|
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| ### Add support for injecting NM config to IPI | ||
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| This might be possible using a recently added [ironic python agent feature](https://specs.openstack.org/openstack/ironic-specs/specs/approved/in-band-deploy-steps.html) | ||
| using that interface, it could be possible to inject network configuration in a | ||
| similar way to coreos-install. | ||
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| However this is a very bleeding edge feature (not yet documented), and it means | ||
| maintaining a custom interface that would be different to both the proven | ||
| uncustomized OSP deploy ramdisk, and the coreos-deploy toolchain. | ||
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| ### Convert IPI to coreos-install based deployment | ||
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| Long term, from an OpenShift perspective, this makes sense as there is overlap | ||
| between the deploy tooling. | ||
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| However in the short/medium term, the IPI deployment components are based on | ||
| Ironic, and that is only really tested with the ironic deploy ramdisk | ||
| (upstream and downstream) - we need to investigate how IPI deployments may be | ||
| adapted to converge with the coreos-install based workflow, but this is likely | ||
| to require considerable planning and development effort to achieve, thus is not | ||
| implementable as an immediate solution. | ||
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| ### Customize images | ||
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| Currently the only option for IPI based deployments is to customize the | ||
| OS image, then provide a locally cached copy of this custom image to the | ||
| installer via the `clusterOSImage` install-config option. | ||
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| This is only a stopgap solution, it is inconvenient for the user, and | ||
| inflexible as it will only work if the configuration required is common | ||
| to every node in the cluster (or for multiple worker machinepools, you | ||
| would require a custom image per pool). |