Add Flow for Minnows; Add VM Minnows Test.

[colemickens]

Summary by CodeRabbit

• New Features

  • Added a FlakeHub edge cache service with configurable caching, DNS, listen addresses, lifetimes, sizing, and storage; includes packaged runtime and startup wiring.

• Tests

  • CI now validates the Minnows VM-based test environment.
  • Added VM-based multi-architecture tests that build and boot images and verify the edge cache service starts successfully.

[coderabbitai]

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📝 Walkthrough

Walkthrough

Adds an nginx-based edge-cache Flow module, Minnows test artifacts (system and flake) that build and vmtest a VM expecting the edge-cache service, and a CI step that runs nix flake check --build-all in test/minnows.

Changes

Edge Cache Service with Test Infrastructure

Layer / File(s)	Summary
Flow module metadata & interface flow.nix	Flow module declares metadata, required capabilities (runAsRoot, fullFilesystemAccess), user/group resources, and interface options for nginx/DNS/listen/cache.
Generated nginx configs flow.nix	Build-time generation of nginx server and runtime configs: pass-through for .narinfo, caching for /nar, and proxy_cache_path configured from inputs.
systemd service and prestart setup flow.nix	Wires systemd.services.flakehub-edge-cache with an ExecStartPre script to create/chown the cache directory and an ExecStart that launches nginx with the generated config.
Minnows system configuration test/minnows/system.nix	Minnows system function that composes platforms, runtime resources, and wires the fec1 flow (importing the edge-cache flow) and a debug-shell flow.
Test flake inputs & outputs helpers test/minnows/flake.nix	Adds flake inputs (nixpkgs follow + Minnows sources), outputs function, supported systems, and helpers to build per-system pkgs/lib.
Per-system minnowsSystems export test/minnows/flake.nix	Exports minnowsSystems.<system>.default by importing ./system.nix with per-system inputs and system.
Per-system vmtest checks test/minnows/flake.nix	Implements checks.<system>.default as a pkgs.runCommand that runs minnows-cli to generate secure-boot state, builds a disk from the bootspec, runs vmtest expecting flow-fec1-flakehub-edge-cache.service, and writes $out.
CI Validation Integration .github/workflows/ci.yml	Adds a checks job step "Check Minnows Test VM" that cds into test/minnows and runs nix flake check --build-all.

Sequence Diagram(s)

sequenceDiagram
  participant CI as CI Workflow
  participant FlakeCheck as "nix flake check --build-all"
  participant MinnowsCLI as minnows-cli
  participant DiskBuilder as Disk build
  participant VMTest as vmtest
  participant EdgeService as flow-fec1-flakehub-edge-cache.service

  CI->>FlakeCheck: run check in test/minnows
  FlakeCheck->>MinnowsCLI: invoke secure-boot generation
  MinnowsCLI->>DiskBuilder: build disk from bootspec
  FlakeCheck->>VMTest: execute vmtest with built disk
  VMTest->>EdgeService: verify service activation
  EdgeService-->>VMTest: service started
  VMTest-->>FlakeCheck: test result

Loading

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• DeterminateSystems/flakehub-edge-cache#1: Prior CI workflow/checks job additions related to running Minnows VM tests.

Suggested reviewers

• grahamc

Poem

A rabbit hops where flakes compile and sing,
Caches hum, nginx keeps a steady ring,
Minnows spin disks, VMs wake and meet,
Services rise, logs whisper "start complete." 🐇

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the two main changes: adding a Flow module (flow.nix) for Minnows and adding a VM-based test suite for Minnows (test/minnows directory with flake.nix and system.nix).
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch colemickens/flow-init

---

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@flow.nix`:
- Around line 98-102: The code references this.tempDirectory but the
tempDirectory option is commented out, causing evaluation errors; either restore
the tempDirectory option block (uncomment and ensure it defines description,
type = flow.lib.types.nullOr flow.lib.types.path, and default =
"/tmp/flakehub-edge-cache") so this.tempDirectory is available, or remove/guard
uses of this.tempDirectory at the call sites (replace direct this.tempDirectory
access with a lookup that falls back to null or remove the dependency). Ensure
changes target the tempDirectory option and all usages of this.tempDirectory.

In `@test/minnows/flake.nix`:
- Around line 29-32: The check references an attribute path that doesn't exist
because minnowsSystems defines minnowsSystems.aarch64-linux.testvm (in the
import of system.nix) but the checks expression expects
inputs.self.minnowsSystems.${system}.default.bootspec; update the minnowsSystems
attribute names or the checks lookup so they match: either expose a top-level
attribute named aarch64-linux (or whatever ${system} expands to) with a
.default.bootspec, or change the checks expression to reference the .testvm
entry (inputs.self.minnowsSystems.${system}.testvm.default.bootspec or adjust
${system} accordingly); locate minnowsSystems, the import of system.nix, and the
checks usage to make names consistent.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 4ac349ae-c13b-4a82-bda4-4b50e5c33f60

📥 Commits

Reviewing files that changed from the base of the PR and between 6bd05b5 and 185851b.

⛔ Files ignored due to path filters (1)

• test/minnows/flake.lock is excluded by !**/*.lock

📒 Files selected for processing (4)

• .github/workflows/ci.yml
• flow.nix
• test/minnows/flake.nix
• test/minnows/system.nix

[coderabbitai]

Actionable comments posted: 0

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@test/minnows/flake.nix`:
- Around line 32-35: The import of system.nix hardcodes system =
"aarch64-linux", causing x86_64 builds to pick the wrong packages; change the
import in the default attribute (the block starting with default = import
./system.nix { inherit inputs; system = ...) to use the incoming closure/system
variable (i.e., pass the existing system instead of the literal "aarch64-linux"
or simply don’t override it) so minnowSystems.x86_64-linux.default resolves with
the correct architecture-specific packages.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 16c93571-3265-4aad-8480-3cf5a647587a

📥 Commits

Reviewing files that changed from the base of the PR and between f88fc60 and eb1b64f.

⛔ Files ignored due to path filters (1)

• test/minnows/flake.lock is excluded by !**/*.lock

📒 Files selected for processing (3)

• .github/workflows/ci.yml
• test/minnows/flake.nix
• test/minnows/system.nix

🚧 Files skipped from review as they are similar to previous changes (2)

• .github/workflows/ci.yml
• test/minnows/system.nix

[coderabbitai]

Actionable comments posted: 0

[coderabbitai]

Actionable comments posted: 0