readme.md

Loop on field of an element

Commands

cue eval *.cue

cue export *.cue --out yaml

Explanations

We can do loop in Cuelang: Official documentation on loop

In the official documentation, it's a loop on a list, in our case, we want a loop on the sub-field port of our deployments.

The template deployments:

deployments: [Name=_]: {
	apiVersion: "apps/v1"
	kind:       "Deployment"
	metadata: {
		name: Name
		labels: {
			app:       Name
			domain:    string | *"prod"
		}
	}
}

The port isn't present in the template because is optional, so we need a condition inside the loop. The official documention on conditional fields.

The loop:

for name, dep in deployments {
	if dep["ports"] != _|_ {

First line: it's a key/value loop on deployments:

• name: name of the deployment
• dep: the data of a deployment

Second line: we test if the field port exist with if dep["ports"] != _|_ . The _|_ is bottom, it's an error or missing field (the documentation on Values):

At the bottom of the lattice is the value called bottom, denoted _|_. A bottom value usually indicates an error. Bottom is an instance of every value.

Important:
Don't use the name of a field as variable of the loop (name and dep in the example). Otherwise, the loop acts strangely.

Then we need to create an element **services** and to use the loop to create every **service**

The template services:

services: [Name=_]: {
	apiVersion: "apps/v1"
	kind:       "Service"
}

and the loop:

for name, dep in deployments {
	if dep["ports"] != _|_ {
	services: "\(name)": {
		spec: selector: dep.metadata.labels

		spec: ports: [
			for p in dep.ports {
				port:       *p | int
				targetPort: *p | int
			},
		]
	}
	}
}

dep refer to the data of the deployment and services to the template of service:

• for name, dep in deployments: a loop on every deployment
• if dep["ports"] != _|_: only if the field ports exist in the deployment
• services: "\(name)": it will create a new service with the name of the deployment (name come from the loop)
• spec: selector: dep.metadata.labels: we use the labels of the deployment as selector of the service
• spec: ports: [: we add a field ports in the new service
• for p in dep.ports {: second loop to map every ports
• port: *p | int and targetPort: *p | int to add source and target port in the service definition

Examples

• the deployments original and changed haven't any port
• the deployment exposed have ports 8080 and 50