From 788cf66f216c5c3499a70b047b05eea0ba0a7e2e Mon Sep 17 00:00:00 2001 From: medusa Date: Wed, 6 Aug 2025 07:39:19 -0500 Subject: [PATCH] Add tech_docs/CUE_your_new_friend.md --- tech_docs/CUE_your_new_friend.md | 222 +++++++++++++++++++++++++++++++ 1 file changed, 222 insertions(+) create mode 100644 tech_docs/CUE_your_new_friend.md diff --git a/tech_docs/CUE_your_new_friend.md b/tech_docs/CUE_your_new_friend.md new file mode 100644 index 0000000..ec7188f --- /dev/null +++ b/tech_docs/CUE_your_new_friend.md @@ -0,0 +1,222 @@ +# **The Complete Technical Guide to CUE (Configure-Unify-Execute)** +*A structured, practical, and comprehensive introduction to CUE—covering core concepts, real-world applications, and best practices.* + +--- + +## **1. Introduction to CUE** +### **What is CUE?** +CUE (**Configure-Unify-Execute**) is an **open-source data constraint language** developed at Google. It is designed for: +- **Configuration management** (Kubernetes, Terraform, CI/CD) +- **Data validation** (API schemas, input sanitization) +- **Code generation** (Dockerfiles, Kubernetes manifests, SQL schemas) +- **Policy enforcement** (security rules, compliance checks) + +Unlike YAML/JSON, CUE merges **types, values, and constraints** into a single model, enabling **deterministic, reproducible configurations**. + +### **Why CUE Over Alternatives?** +| Tool | Strengths | Weaknesses vs. CUE | +|--------------|-----------------------------|---------------------------------| +| **YAML** | Human-readable, widely used | No validation, no logic, fragile | +| **Jsonnet** | Templating, code reuse | Slower, no built-in validation | +| **HCL** | Terraform integration | Less flexible for non-TF use | +| **Pulumi** | Full programming model | Complex, runtime-dependent | +| **CUE** | **Validation + unification** | Steeper initial learning curve | + +--- + +## **2. Core Concepts** +### **The CUE Lattice** +CUE’s power comes from its **lattice structure**, where: +- **`_` (Top)**: Accepts any value (e.g., `string`, `int`, `{}`). +- **`_|_` (Bottom)**: An invalid/conflicting value (error state). +- **Unification (`&`)** combines constraints (like logical AND). +- **Disjunction (`|`)** allows alternatives (like logical OR). + +**Example:** +```cue +#Schema: { + name: string & =~"^[A-Z][a-z]+$" // Must start with uppercase + age: int & >0 & <120 // Age between 0 and 120 + role?: "admin" | "user" // Optional role +} + +valid: #Schema & { name: "Alice", age: 30 } // ✅ Valid +invalid: #Schema & { name: "alice", age: 150 } // ❌ Fails (name, age) +``` + +--- + +## **3. Getting Started** +### **Installation** +```bash +# Install CUE +brew install cue-lang/tap/cue # macOS +sudo apt-get install cue # Debian/Ubuntu +go install cuelang.org/go/cmd/cue@latest # Go users + +# Verify +cue version +``` + +### **Basic Workflow** +1. **Define schemas** (`.cue` files). +2. **Validate data** (`cue vet`). +3. **Export to JSON/YAML** (`cue export`). + +**Example:** +```cue +// schema.cue +#Person: { + name: string + age: int & >=18 +} + +// data.json +{ "name": "Bob", "age": 25 } + +# Validate +cue vet schema.cue data.json # ✅ Passes +``` + +--- + +## **4. Real-World Use Cases** +### **Case 1: Kubernetes Configuration** +**Problem**: YAML files are brittle and hard to validate. +**Solution**: Define a reusable schema. + +```cue +// k8s.cue +#Deployment: { + apiVersion: "apps/v1" + kind: "Deployment" + metadata: name: string + spec: { + replicas: int & >=1 + template: spec: containers: [{ + name: string + image: string & =~".+:.+" + }] + } +} + +myapp: #Deployment & { + metadata: name: "webapp" + spec: replicas: 3 + spec: template: spec: containers: [{ name: "app", image: "nginx:latest" }] +} + +# Export to YAML +cue export k8s.cue -e myapp --out yaml > deploy.yaml +``` + +### **Case 2: Terraform Guardrails** +**Problem**: Prevent invalid cloud configurations. +**Solution**: Enforce AWS/GCP policies. + +```cue +#AWS: { + region: "us-east-1" | "us-west-2" + instanceType: "t2.micro" | "t3.medium" +} + +my_vm: #AWS & { + region: "us-east-1" + instanceType: "t2.micro" # ✅ Valid +} + +invalid_vm: #AWS & { + region: "eu-west-1" # ❌ Fails (invalid region) +} +``` + +### **Case 3: CI/CD Pipeline-as-Code** +**Problem**: YAML-based pipelines are hard to maintain. +**Solution**: Define pipelines in CUE. + +```cue +#Pipeline: { + steps: [...{ + name: string + cmd: string + }] +} + +my_pipeline: #Pipeline & { + steps: [ + { name: "build", cmd: "go build" }, + { name: "test", cmd: "go test" }, + ] +} + +# Generate GitHub Actions YAML +cue export pipeline.cue --out yaml > .github/workflows/ci.yml +``` + +--- + +## **5. Debugging & Best Practices** +### **Debugging Unification Errors** +- Use `cue eval -v` to trace unification steps. +- Check for `_|_` (bottom) in output—indicates conflicts. + +### **Best Practices** +1. **Modularize**: Split schemas into files (`schemas/`, `configs/`). +2. **Reuse**: Leverage CUE’s **import system** (`import "acme.com/schemas"`). +3. **Validate Early**: Run `cue vet` in CI/CD. + +--- + +## **6. Advanced Topics** +### **Go + CUE Integration** +Embed CUE in Go programs for dynamic validation: +```go +package main + +import ( + "cuelang.org/go/cue/cuecontext" + "fmt" +) + +func main() { + ctx := cuecontext.New() + schema := ctx.CompileString(` + #Person: { + name: string + age: int & >=18 + }`) + data := ctx.CompileString(`{ name: "Alice", age: 30 }`) + + unified := schema.Unify(data) + if err := unified.Validate(); err != nil { + fmt.Println("Validation failed:", err) + } else { + fmt.Println("Valid!") + } +} +``` + +### **Generating Code** +Convert CUE to: +- **OpenAPI**: `cue export --out openapi` +- **Go Structs**: `cue get go` +- **SQL**: Use templates (`text/template`). + +--- + +## **7. Learning Resources** +- **Official Docs**: [cuelang.org](https://cuelang.org/) +- **Playground**: [cuelang.org/play](https://cuelang.org/play) +- **Community**: [CUE Slack](https://cuelang.slack.com/) + +--- + +## **Conclusion** +CUE replaces **ad-hoc YAML/JSON** with **structured, validated, and reusable** configurations. By mastering: +1. **Lattice logic** (unification, constraints), +2. **Real-world workflows** (K8s, Terraform, CI/CD), +3. **Tooling integration** (Go, OpenAPI), + +You can eliminate configuration errors and enforce policies **declaratively**. + +**Next Step**: Try the [CUE Tutorial](https://cuelang.org/docs/tutorials/) or experiment in the **playground**! 🚀 \ No newline at end of file