the_information_nexus/tech_docs/CUE.md

Welcome to the world of CUE – Configure-Unify-Execute – a language that turns the usual “write YAML and pray” workflow into something that feels almost… serendipitous.

In CUE you don’t imperatively build configs, websites, DB schemas, or API specs.
Instead you declare the shape, constraints and defaults you want, then let CUE’s graph-unification engine search the (enormous but finite) space of legal values and hand you back the one deterministic result that satisfies every rule.
That moment when cue export suddenly spits out the exact JSON or SQL DDL you needed? Deterministic serendipity – reproducible, cacheable, diff-able.

A 30-second taste:

package site

#Page: {
    title: string & =~"^[A-Z].*"
    path:  string & =~"^/[a-z0-9/-]+$"
    meta: {
        description: string & strings.MinRunes(30) & strings.MaxRunes(160)
        keywords:    [...string] & list.Unique()
    }
}

home: #Page & {
    title: "Welcome to the World of CUE"
    path:  "/"
    meta: keywords: ["cue", "configure", "unify", "execute"]
}

Run cue export home and you get the exact JSON your static-site generator needs, with every constraint already proven.
Change a single keyword and CUE re-unifies, yielding a new but still deterministic artefact.

The same file can:

• generate OpenAPI specs, Terraform, Kubernetes YAML
• validate incoming JSON requests at runtime
• spit out SQL DDL and Go structs (cue get go) or even HTML via a tiny script

Because CUE merges types, values and constraints into one concept, the usual inheritance hell disappears: you compose by unification (&) instead of copy-paste or fragile overrides.

So yes – in the CUE universe you write a handful of declarations, run cue, and the “accidental” correct configuration pops out every single time.
Raw deterministic serendipity, no runtime surprises, no “works on my machine”.

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CUE (Configure-Unify-Execute) is an open-source data constraint language developed at Google, designed for configuration management, validation, and templating. It stands for Configure, Unify, Execute.

Purpose

CUE simplifies tasks involving defining, validating, and using data in complex systems like Kubernetes. It combines schemas, constraints, and values into a unified framework, ensuring configurations adhere to predefined rules.

Key Features

• Validation First: Unlike traditional languages, CUE prioritizes validation, ensuring data meets strict criteria.
• JSON Superset: It builds upon JSON, adding logic like conditionals and loops.
• Constraint-Based: Uses constraints instead of inheritance, avoiding complexity from order-dependent merging.
• Order Independence: Merging configurations is associative, commutative, and idempotent, ensuring consistency regardless of merge order.
• Tooling: Offers CLI tools (cue command), APIs for automation, and integrations with YAML/JSON.

Use Cases

• Kubernetes: Validate and generate YAML configurations.
• Data Validation: Define schemas for APIs or infrastructure.
• Code Generation: Extract schemas from source code or generate code from CUE definitions.
• CI/CD Pipelines: Ensure deployment consistency.

Example

In CUE, you might define a schema for a Kubernetes deployment, enforce constraints (e.g., resource limits), and generate validated YAML—all in one workflow.

Summary

CUE is a robust, constraint-driven language that unifies configuration, validation, and execution, particularly valuable for managing complex, policy-driven systems like cloud infrastructure.

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Here are six starter ideas that feel more like “mini-projects” than “hello-world” exercises. Each one is scoped to be finished in an evening or weekend and leaves you with something useful you can actually commit to a repo or show a teammate.

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1. “Pet-Picture” API Contract
   • Goal: Design the request/response contract for a tiny REST service that lets users POST pictures of their pets.
   • CUE angle
   – Write a #PetPhoto schema with required fields (id, petName, imageURL), plus constraints (URL must start with https://, file size ≤ 5 MB, allowed MIME types).
   – Export the same CUE to JSON Schema so front-end folks can use it in Swagger / OpenAPI.
   • Quick win: curl a sample payload through cue vet in CI and watch it reject the 6 MB GIF someone tried to sneak in .

2. Terraform Variable Guardrails
   • Goal: Stop teammates from fat-fingering Azure VM sizes or AWS regions in your Terraform repo.
   • CUE angle
   – Describe all valid regions, SKUs, and tag patterns in CUE.
   – Make a variables.cue that unifies with every .tfvars file in the repo; fail the plan if anything is wrong .
   • Quick win: open a PR that deliberately violates the policy and see GitHub Actions reject it in <30 s.

3. Team Dotfiles Distribution
   • Goal: Ship a single YAML/JSON file per engineer that declares their preferred shell, VS Code extensions, and git aliases.
   • CUE angle
   – Provide a #Workstation schema with defaults (shell = "zsh", extensions = [ "GitLens", "k9s" ]).
   – Write a 20-line Go program that ingests the unified CUE value and spits out the right Ansible or Home-Brew bundle per person .

4. Kubernetes “Golden Path” Templates
   • Goal: Give devs a one-command way to generate a Deployment + Service + HPA that already meets security and resource standards.
   • CUE angle
   – Create a #Microservice definition that enforces labels, resource limits, and security contexts.
   – Provide optional overlays (staging vs prod) that inject different image registries or replica counts .
   • Quick win: cue cmd gen prod my-app writes prod-my-app.yaml with zero copy-paste.

5. Resume-as-Data
   • Goal: Host your résumé as YAML but still be able to export to PDF, JSON, and HTML.
   • CUE angle
   – Model sections (experience, education, skills) with strict types and regex rules (company names must match LinkedIn URLs).
   – Use cue export to feed a Go template that renders LaTeX or Markdown.
   • Quick win: change one bullet in YAML, rerun make and see every output format refresh.

6. Advent-of-Code Input Validator
   • Goal: Stop wasting time on malformed puzzle inputs.
   • CUE angle
   – For any AoC day, capture the input grammar in CUE (grids, ints, regex groups).
   – Add constraints (board size 100×100, numbers 0-9 only).
   • Quick win: paste your downloaded input into input.txt; cue vet tells you immediately if the site changed the format overnight.

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How to pick one
• If you live in Terraform → start with #2.
• If you just want to “see CUE do magic” → #1 or #5 finishes in <30 min.
• If you’re already on K8s → #4 will save you real toil next sprint.

Each repo can literally be a folder with a schema.cue, a data.* file, and a two-line GitHub Action that runs cue vet. Ship it, tag a friend for review, and you’ve officially gone from “reading about CUE” to “running CUE in production.”

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Below is a step-by-step brainstorm that keeps the promise:
“Everything is an object” → expressed in CUE → rendered into one or more Docker containers → deployed on stock Debian.

We iterate together—after each numbered idea you can simply reply “next” or “deep-dive ” and I’ll expand only the one you like.

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1. Object–Music Player (OM-Player)
   • Object model: every track, playlist, device, volume-level, EQ preset is a CUE object.
   • CUE → Docker trick: cue export om.cue | cue cmd gen docker-compose.yml yields three containers (MPD server, web-UI, icecast stream).
   • Deploy: ./deploy.sh on a Debian box auto-pulls images, mounts /music, and exposes port 8000.
   • Hook: you can change “cross-fade = 2.0s” in the CUE file, run cue vet, and the compose file re-renders without touching YAML by hand.

2. Object–Photo Darkroom (OM-Darkroom)
   • Object model: raw image, transform pipeline (crop 1:1 → denoise → LUT), export profiles.
   • CUE → Docker trick: single multi-stage Dockerfile generated from CUE; includes conditional GPU layer if gpu: true.
   • Deploy: on Debian with or without NVIDIA Docker runtime .
   • Hook: cue eval darkroom.cue shows you the exact ImageMagick CLI that will run inside the container before you ever build.

3. Object–Home-Lab Router (OM-Router)
   • Object model: interface objects, VLAN objects, nftables rule objects, WireGuard peer objects.
   • CUE → Docker trick: produces a privileged container that maps /etc/wireguard, /etc/nftables; plus a dry-run sidecar container that just prints the rules it would apply.
   • Deploy: systemd service on Debian host starts the container at boot.
   • Hook: cue vet guarantees that no two VLANs share the same ID, no overlapping subnets, etc.

4. Object–FaaS Edge (OM-Edge)
   • Object model: every function is an object (fn, runtime, env, memory, cpu).
   • CUE → Docker trick: CUE spawns one container per function plus an nginx reverse-proxy container.
   • Deploy: Debian box becomes a mini Lambda—curl /fn/hello triggers the container of the moment.
   • Hook: horizontal scale is just changing replicas: 3 in CUE and re-exporting.

5. Object–Minecraft World (OM-Mine)
   • Object model: world seed, player objects, permission objects, mod objects.
   • CUE → Docker trick: Server container + optional RCON web UI container.
   • Deploy: on Debian; mods are baked into the image hash calculated from the CUE file.
   • Hook: roll back to yesterday’s world by reverting one Git commit to the CUE file and redeploying.

6. Object–CI Matrix (OM-Matrix)
   • Object model: every job, step, runner label, secret ref is an object.
   • CUE → Docker trick: generates a lightweight Drone-CI server + runner containers.
   • Deploy: single docker compose up on Debian; self-hosted CI in < 2 min.
   • Hook: matrix expansion (go: [1.21, 1.22]) happens in CUE, not in YAML anchors.

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Your turn
Reply with the number you want to pursue (or say “new batch”) and I’ll give:

1. Minimal CUE schema
2. Exact docker-compose.yml generator snippet
3. One-liner to run it on a fresh Debian install

Yes — there are very concrete reasons to pair Go + CUE that do not apply (or apply only weakly) to other language stacks.
Below is a concise decision grid you can paste into an ADR or RFC.

Benefit	Why it matters	Go + CUE	Other stacks
Single binary, zero runtime	Shipping a CLI to ops/DevOps that “just works”	go build produces a static binary that embeds CUE via cuelang.org/go	Node, Python, etc. need a runtime and dependency tree
Schema ↔ code round-trip	Keep Go structs as the source-of-truth and still get CUE validation	cue get go k8s.io/api/apps/v1 auto-generates CUE from Go types; cue export can spit JSON/YAML back out	Other languages have to hand-write schemas or use separate tools
Cloud-native lingua franca	Every major infra tool (K8s, Terraform, Helm, Docker, Dagger, Argo CD) is written in Go	You can import their Go packages and generate CUE constraints without re-implementing anything	Python/Node/Java must FFI or re-implement
Rich Go API	Load, unify, validate, diff, trim configs inside your program	Full lattice operations (unify, subsumption, export) via cuecontext and cue/load	Only shell-out or WASM today for non-Go
Performance	Parse & validate 1000s of YAML manifests in CI	Pure Go, no CGO; benchmarks show ~2× faster than Starlark/Jsonnet on large k8s repos	Python/Node bindings pay serialization cost
Policy-as-code reuse	Embed the same constraints in admission webhooks, CLIs, or controllers	Import CUE in Go controller code; compile once, run everywhere	Rego (OPA) needs separate runtime; Jsonnet is turing-complete & slower
Community & tooling	KubeVela, Dagger, Grafana, Holos, etc. all expose Go SDKs that expect CUE	Shared libraries and examples	Smaller, fragmented ecosystems outside Go

When not to pick Go + CUE

• Your service is purely browser/Node → TypeScript + JSON Schema or Zod is lighter.
• You need end-user scripting (e.g., Terraform custom providers) → HCL/Starlark still wins on mind-share.
• You target resource-constrained embedded → CUE’s Go runtime is heavier than a hand-rolled C validator.

TL;DR

If you are already in the Go / cloud-native orbit, Go + CUE is the only combination today that lets you keep your existing types, ship a single static CLI, and reuse the exact same constraints in controllers, CI, and documentation generators .