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StackKits use CUE as their schema language. Understanding this architecture helps you customize kits and create your own.

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Why CUE?

CUE (Configure, Unify, Execute) provides something that YAML and JSON Schema cannot: types, constraints, and composition in a single language. 
// CUE catches errors that YAML cannot
#Service: {
    name:    string & =~"^[a-z][a-z0-9-]*$"
    port:    int & >0 & <65536
    enabled: bool | *true  // default: true
}
Key advantages:
  • Type safety — Catch configuration errors before deployment
  • Composable — Kits can extend and override each other
  • Defaults — Sensible defaults reduce configuration burden
  • Constraints — Express rules like “port must be > 1024” or “domain must be valid”

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Three-layer architecture

Every StackKit follows a three-layer model:
  1. OS Layer — Base operating system configuration, security hardening, networking
  2. Platform Layer — Container runtime (Docker Compose), standard networks, volumes
  3. Application Layer — Modular services that users select and configure

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How validation works

When you run kombify validate, your kombination.yaml is checked against the CUE schema of your selected StackKit:
1

Schema loading

The StackKit’s CUE schema is loaded, including all layer definitions and constraints.
2

Unification

Your configuration is unified with the schema. CUE checks that every value satisfies its type and constraints.
3

Default resolution

Missing optional values are filled with CUE defaults.
4

Error reporting

Any validation errors are reported with clear messages indicating what went wrong and where.

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Extending kits

StackKits are designed to be extended. You can:
  • Override defaults — Change any default value in your kombination.yaml
  • Add services — Include additional services not in the base kit
  • Customize layers — Modify OS or platform settings for your environment

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Further reading

Spec-driven design

The philosophy behind declarative infrastructure

Available kits

Browse the StackKit catalog