mirror of
https://github.com/vmware-tanzu/velero.git
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Micah NagelandXun Jiang/Bruce Jiang
3244cc605f
Signed-off-by: Micah Nagel <micah.nagel@defenseunicorns.com>
71 lines
4.4 KiB
Markdown
71 lines
4.4 KiB
Markdown
# Apply flag for install command
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## Abstract
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Add an `--apply` flag to the install command that enables applying existing resources rather than creating them. This can be useful as part of the upgrade process for existing installations.
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## Background
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The current Velero install command creates resources but doesn't provide a direct way to apply updates to an existing installation.
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Users attempting to run the install command on an existing installation receive "already exists" messages.
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Upgrade steps for existing installs typically involve a three (or more) step process to apply updated CRDs (using `--dry-run` and piping to `kubectl apply`) and then updating/setting images on the Velero deployment and node-agent.
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## Goals
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- Provide a simple flag to enable applying resources on an existing Velero installation.
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- Use server-side apply to update existing resources rather than attempting to create them.
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- Maintain consistency with the regular install flow.
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## Non Goals
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- Implement special logic for specific version-to-version upgrades (i.e. resource deletion, etc).
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- Add complex upgrade validation or pre/post-upgrade hooks.
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- Provide rollback capabilities.
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## High-Level Design
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The `--apply` flag will be added to the Velero install command.
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When this flag is set, the installation process will use server-side apply to update existing resources instead of using create on new resources.
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This flag can be used as _part_ of the upgrade process, but will not always fully handle an upgrade.
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## Detailed Design
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The implementation adds a new boolean flag `--apply` to the install command.
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This flag will be passed through to the underlying install functions where the resource creation logic resides.
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When the flag is set to true:
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- The `createOrApplyResource` function will use server-side apply with field manager "velero-cli" and `force=true` to update resources.
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- Resources will be applied in the same order as they would be created during installation.
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- Custom Resource Definitions will still be processed first, and the system will wait for them to be established before continuing.
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The server-side apply approach with `force=true` ensures that resources are updated even if there are conflicts with the last applied state.
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This provides a best-effort mechanism to apply resources that follows the same flow as installation but updates resources instead of creating them.
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No special handling is added for specific versions or resource structures, making this a general-purpose mechanism for applying resources.
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## Alternatives Considered
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1. Creating a separate `upgrade` command that would duplicate much of the install command logic.
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- Rejected due to code duplication and maintenance overhead.
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2. Implementing version-specific upgrade logic to handle breaking changes between versions.
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- Rejected as overly complex and difficult to maintain across multiple version paths.
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- This could be considered again in the future, but is not in the scope of the current design.
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3. Adding automatic detection of existing resources and switching to apply mode.
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- Rejected as it could lead to unexpected behavior and confusion if users unintentionally apply changes to existing resources.
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## Security Considerations
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The apply flag maintains the same security profile as the install command.
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No additional permissions are required beyond what is needed for resource creation.
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The use of `force=true` with server-side apply could potentially override manual changes made to resources, but this is a necessary trade-off to ensure apply is successful.
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## Compatibility
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This enhancement is compatible with all existing Velero installations as it is a new opt-in flag.
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It does not change any resource formats or API contracts.
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The apply process is best-effort and does not guarantee compatibility between arbitrary versions of Velero.
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Users should still consult release notes for any breaking changes that may require manual intervention.
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This flag could be adopted by the helm chart, specifically for CRD updates, to simplify the CRD update job.
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## Implementation
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The implementation involves:
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1. Adding support for `Apply` to the existing Kubernetes client code.
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1. Adding the `--apply` flag to the install command options.
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1. Changing `createResource` to `createOrApplyResource` and updating it to use server-side apply when the `apply` boolean is set.
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The implementation is straightforward and follows existing code patterns.
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No migration of state or special handling of specific resources is required.
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