Add tech_docs/CUE_your_new_friend.md
This commit is contained in:
222
tech_docs/CUE_your_new_friend.md
Normal file
222
tech_docs/CUE_your_new_friend.md
Normal file
@@ -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**! 🚀
|
||||
Reference in New Issue
Block a user