CUE in practice

This page walks through building a real config against jaque’s schema, with snippets you can copy and adapt.

The smallest config

hosts: gw: {
  address: "192.168.1.1"
  check: {type: "icmp", host: address}
}

One host, ICMP checked every 60 seconds (#Schedule’s default). host: address reuses the field you just set two lines up — CUE resolves references within the same struct, so you’re not retyping the IP.

A host with a service

hosts: gw: {
  address: "192.168.1.1"
  check:   {type: "icmp", host: "192.168.1.1"}
  services: web: check: {type: "http", url: "http://192.168.1.1/"}
}

Every service under a host is checked independently, with its own #Schedule — a service doesn’t inherit its host’s check_interval unless you make it.

A shared template

Ten devices of the same kind shouldn’t repeat their check config ten times: anchor a partial struct on #Host (or #Check) and unify it at each use site. See Why CUE for the #CastDevice example and why anchoring on the schema, not a bare struct, is what makes this safe to do at scale.

Contacts, a policy, and an escalation

contacts: {
  alice: {type: "email", address: "[email protected]"}
  oncall_hook: {type: "webhook", url: "https://hooks.example.com/oncall"}
}

notifications: business_hours: {
  period: [
    {weekday: "monday", start: "09:00", end: "17:00"},
  ]
  levels: [
    {contacts: ["alice"], threshold: 3, renotify_interval: "30m"},
    {contacts: ["oncall_hook"], renotify_interval: "10m"},
  ]
}

hosts: gw: {
  address: "192.168.1.1"
  check: {type: "icmp", host: "192.168.1.1"}
  notification: "business_hours"
}

Full detail — every contact type, escalation semantics, windows — is in Contacts and policies and Escalations and windows.

Labels and views

hosts: web: {
  address: "10.0.0.1"
  check:   {type: "icmp", host: "10.0.0.1"}
  labels:  {env: "prod", role: "web"}
}

views: prod: selector: "env=prod"

See Labels and views for selector grammar and what a saved view actually is.

Zones

zone defaults to "default" on a host; a service’s zone defaults to "", which inherits the host’s:

hosts: gw: {zone: "eu-west"}
services: web: {}  // inherits "eu-west"

Validating a config

There’s no separate jaque validate — loading is validating:

jaque -config yourfile.cue

Validation happens in two phases and fails differently depending on which one catches the problem — see Why CUE for the distinction between a schema-constraint failure (unknown field, wrong type) and a concretion failure (a value left unresolved). Either way, the error names the field, not just “config invalid”.