Initial user stanza support & architecture review by navaneeth-dev · Pull Request #7 · flatcar/Butane-init

navaneeth-dev · 2026-09-17T14:41:07Z

Summary

add the bt Cobra CLI for converting cloud-config YAML to Butane YAML
support the initial Cluster API worker users subset: name, password hash, GECOS, home directory, shell, and SSH authorized keys
reject unsupported or malformed input instead of silently producing a partial conversion
preserve cloud-init's default locked-password behavior
document the supported fields and current limitations
Added GitHub Actions CI for unit testing, will add QEMU tests soon

Testing

validated generated output with Butane v0.29.0 in strict mode
booted Flatcar Stable under QEMU/KVM and verified SSH login, GECOS, custom home directory, shell, locked password, and authorized key provisioning

Signed-off-by: Navaneeth <me@rizexor.com>

Copilot

🟢 Approval recommended

The changes are cohesive, well-tested with clear rejection semantics, and CI is in place to enforce build/vet/test for the new CLI and transpiler logic.

Pull request overview

Adds an initial bt CLI and a strict cloud-config → Butane transpiler focused on the Cluster API worker users subset, with validation and unit tests, aligning with the repo’s goal of a minimal but correct conversion path for Cluster API provisioning.

Changes:

Introduce a Cobra-based bt CLI that reads cloud-config from a file or stdin and writes Butane YAML to stdout or an output file (atomic write).
Implement strict transpilation for the supported users subset, rejecting unsupported fields, YAML aliases/anchors, multiple documents, and missing #cloud-config headers, and validating the generated Butane via butane.TranslateBytes.
Add unit tests plus fixture documentation and GitHub Actions CI for build/vet/test.

File summaries

File	Description
README.md	Documents `bt` usage, supported `users` fields, and current limitations.
main.go	Adds the `bt` Cobra CLI, input handling, and atomic output writing.
main_test.go	Tests CLI stdin→stdout behavior and output file permissions.
internal/transpile/transpile.go	Implements strict parsing/validation and Butane generation + validation.
internal/transpile/users.go	Parses and validates the supported `users` fields and maps them to Butane `passwd.users`.
internal/transpile/transpile_test.go	Adds fixture-driven unit tests for success and rejection cases.
internal/transpile/testdata/README.md	Documents the provenance and purpose of fixtures.
internal/transpile/testdata/cluster-api-supported-user.yaml	Success fixture covering supported `users` fields.
internal/transpile/testdata/cluster-api-groups.yaml	Rejection fixture for groups-related fields.
internal/transpile/testdata/cluster-api-deferred-fields.yaml	Rejection fixture for deferred/unsupported account-policy fields.
go.mod	Introduces module definition and dependencies.
go.sum	Adds dependency checksums.
.github/workflows/ci.yml	Adds CI workflow to build, vet, and test on push/PR.

Review details

Files reviewed: 12/13 changed files
Comments generated: 0
Review effort level: Lite

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The standalone Butane module is deprecated. Use the public Butane packages shipped in Ignition v2.27.0 and raise the Go version to the dependency's required Go 1.25. Signed-off-by: Navaneeth <me@rizexor.com>

Copilot

🔵 Needs a closer look

The Jinja template rejection logic can be bypassed when the directive appears after #cloud-config, contradicting the documented “rejected” behavior.

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

internal/transpile/transpile.go:104

validateCloudConfigHeader() returns as soon as it sees #cloud-config, so a ## template: jinja line that appears after the header would not be rejected even though the README states Jinja templates are rejected. This can lead to silently accepting templated configs depending on directive placement.

Files reviewed: 12/13 changed files
Comments generated: 0 new
Review effort level: Lite

elmiko

i think this is looking nice for an initial configuration. i have a question about the combined error return from the Transpile function.

also, i'm curious if you plan to make a test file for the users.go, or will it be tested through the transpile_test.go ?

Represent validation failures as typed problems so callers can inspect paths and source locations without parsing the human-readable error message. Signed-off-by: Navaneeth <me@rizexor.com>

navaneeth-dev · 2026-09-18T14:35:35Z

Refactored to users_test.go and future stanzas will also be done like this.

Keep document-level checks in transpile_test.go and group user-specific behavior in users_test.go while preserving the public Transpile test seam. Signed-off-by: Navaneeth <me@rizexor.com>

navaneeth-dev · 2026-09-18T14:37:46Z

Is there a public Go lib to validate Butane? Currently using https://pkg.go.dev/github.com/coreos/ignition but last update is 2 years back?

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Signed-off-by: Navaneeth <me@rizexor.com>

Update the shared fixture helper after testdata was renamed to testcases so users tests resolve the existing fixture files again. Signed-off-by: Navaneeth <me@rizexor.com>

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elmiko · 2026-09-18T15:05:31Z

Is there a public Go lib to validate Butane? Currently using https://pkg.go.dev/github.com/coreos/ignition but last update is 2 years back?

that's a good question, i'm not sure. perhaps @tormath1 knows?

elmiko

i think this is looking good, no further comments from my side.

/lgtm

tormath1 · 2026-09-21T08:39:35Z

Is there a public Go lib to validate Butane? Currently using https://pkg.go.dev/github.com/coreos/ignition but last update is 2 years back?

Given the very recent merge of Butane into Ignition (https://github.com/coreos/ignition/pull/2235/changes#diff-fe44f09c4d5977b5f5eaea29170b6a0748819c9d02271746a20d81a5f3efca17R18), I think the best way to proceed is to import the module as:

 "github.com/coreos/ignition/v2/butane/config"

As you actually did, you need to add 'v2' suffix to your link to get the current doc: https://pkg.go.dev/github.com/coreos/ignition/v2

tormath1

Thanks, it looks good for a first iteration. :)

Co-authored-by: Mathieu Tortuyaux <mathieu.tortuyaux@gmail.com> Signed-off-by: Navaneeth Rao <me@rizexor.com>

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Co-authored-by: Mathieu Tortuyaux <mathieu.tortuyaux@gmail.com> Signed-off-by: Navaneeth Rao <me@rizexor.com>

Copilot

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Move the library from internal/transpile to the module root so Cluster API and other consumers can import it. Move the bt executable to cmd/bt and keep fixtures with the root package tests. Signed-off-by: Navaneeth <me@rizexor.com>

Use Go 1.27 for local builds and CI through the version declared in go.mod. Signed-off-by: Navaneeth <me@rizexor.com>

Build output with the Ignition v2 Flatcar and passwd types. Use the YAML zero-value omission option to avoid emitting unsupported empty sections. Signed-off-by: Navaneeth <me@rizexor.com>

Inspect only the first input line because Jinja, cloud-config, and invalid input exhaust the supported header states. Cover a leading blank line as an invalid header. Signed-off-by: Navaneeth <me@rizexor.com>

Check dependency sources into vendor and force CI build, vet, and test commands to use them without downloading modules. Signed-off-by: Navaneeth <me@rizexor.com>

Copilot

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

navaneeth-dev · 2026-09-23T16:12:30Z

Done

navaneeth-dev added 7 commits September 16, 2026 22:50

feat(transpile): add users cloud-config support

ae5fdcf

Signed-off-by: Navaneeth <me@rizexor.com>

fix(cli): restrict output file permissions

6dfe937

Signed-off-by: Navaneeth <me@rizexor.com>

ci: add Go checks

5d2dd3c

Signed-off-by: Navaneeth <me@rizexor.com>

fix(transpile): reject Jinja templates

2975b51

Signed-off-by: Navaneeth <me@rizexor.com>

test: add Cluster API cloud-config fixtures

bdbcc0d

Signed-off-by: Navaneeth <me@rizexor.com>

refactor: move CLI to module root

e78b181

Signed-off-by: Navaneeth <me@rizexor.com>

refactor(transpile): extract users stanza

d634782

Signed-off-by: Navaneeth <me@rizexor.com>

navaneeth-dev self-assigned this Sep 17, 2026

navaneeth-dev requested a review from a team as a code owner September 17, 2026 14:41

navaneeth-dev requested review from elmiko and tormath1 and a lite review from Copilot September 17, 2026 14:41

Copilot started reviewing on behalf of navaneeth-dev September 17, 2026 14:42 View session

Copilot AI reviewed Sep 17, 2026

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build(deps): migrate Butane to Ignition module

8f8ff1a

The standalone Butane module is deprecated. Use the public Butane packages shipped in Ignition v2.27.0 and raise the Go version to the dependency's required Go 1.25. Signed-off-by: Navaneeth <me@rizexor.com>

Copilot AI review requested due to automatic review settings September 17, 2026 15:20

Copilot started reviewing on behalf of navaneeth-dev September 17, 2026 15:21 View session

Copilot AI reviewed Sep 17, 2026

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elmiko reviewed Sep 17, 2026

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Comment thread transpile.go

feat(transpile): expose structured validation errors

bc5885d

Represent validation failures as typed problems so callers can inspect paths and source locations without parsing the human-readable error message. Signed-off-by: Navaneeth <me@rizexor.com>

test(transpile): separate users coverage

e84a769

Keep document-level checks in transpile_test.go and group user-specific behavior in users_test.go while preserving the public Transpile test seam. Signed-off-by: Navaneeth <me@rizexor.com>

Copilot AI review requested due to automatic review settings September 18, 2026 14:39

Copilot AI reviewed Sep 18, 2026

chore: rename testdata to testcases

ee3b4eb

Signed-off-by: Navaneeth <me@rizexor.com>

navaneeth-dev force-pushed the feat/users branch from d84a46a to ee3b4eb Compare September 18, 2026 14:40

fix(test): follow renamed fixture directory

e96be58

Update the shared fixture helper after testdata was renamed to testcases so users tests resolve the existing fixture files again. Signed-off-by: Navaneeth <me@rizexor.com>

Copilot AI review requested due to automatic review settings September 18, 2026 14:43

Copilot AI reviewed Sep 18, 2026

elmiko reviewed Sep 18, 2026

View reviewed changes

elmiko approved these changes Sep 18, 2026

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tormath1 reviewed Sep 21, 2026

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chore: use latest flatcar butane version

c9dea21

Co-authored-by: Mathieu Tortuyaux <mathieu.tortuyaux@gmail.com> Signed-off-by: Navaneeth Rao <me@rizexor.com>

Copilot AI review requested due to automatic review settings September 23, 2026 13:55

Copilot AI reviewed Sep 23, 2026

fix: proper error msg for validating header

eeaf7a2

Co-authored-by: Mathieu Tortuyaux <mathieu.tortuyaux@gmail.com> Signed-off-by: Navaneeth Rao <me@rizexor.com>

Copilot AI review requested due to automatic review settings September 23, 2026 13:56

Copilot AI reviewed Sep 23, 2026

navaneeth-dev added 5 commits September 23, 2026 19:44

refactor: expose transpiler at module root

8508f88

Move the library from internal/transpile to the module root so Cluster API and other consumers can import it. Move the bt executable to cmd/bt and keep fixtures with the root package tests. Signed-off-by: Navaneeth <me@rizexor.com>

build: require Go 1.27

73afbdf

Use Go 1.27 for local builds and CI through the version declared in go.mod. Signed-off-by: Navaneeth <me@rizexor.com>

refactor: use upstream Butane schema types

423ebda

Build output with the Ignition v2 Flatcar and passwd types. Use the YAML zero-value omission option to avoid emitting unsupported empty sections. Signed-off-by: Navaneeth <me@rizexor.com>

refactor: validate cloud-config header directly

cc1b0b7

Inspect only the first input line because Jinja, cloud-config, and invalid input exhaust the supported header states. Cover a leading blank line as an invalid header. Signed-off-by: Navaneeth <me@rizexor.com>

build: vendor Go dependencies

f0e8fcc

Check dependency sources into vendor and force CI build, vet, and test commands to use them without downloading modules. Signed-off-by: Navaneeth <me@rizexor.com>

Copilot AI review requested due to automatic review settings September 23, 2026 16:11

Copilot AI reviewed Sep 23, 2026

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navaneeth-dev commented Sep 17, 2026

Summary

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🟢 Approval recommended

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🔵 Needs a closer look

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navaneeth-dev commented Sep 18, 2026

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tormath1 commented Sep 21, 2026 •

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