Simplifying Configuration

Demo

Simple Deployment

YAML

kubectl get all -A

kubectl apply -f simple/nginx.yaml

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

kubectl delete -f simple/nginx.yaml

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

CUE

cue import -l 'kind' -l 'metadata.name' -p demo -f simple/nginx.yaml

cue export simple/nginx.cue

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' simple/nginx.cue

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' simple/nginx.cue | kubectl apply -f -

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' simple/nginx.cue | kubectl delete -f -

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

Pulling Up Configuration

cue mod init

cat >demo.cue <<EOF
package demo

Namespace: [Name=string]: {
	apiVersion: "v1"
	kind:       "Namespace"
	metadata: {
		name: Name
		labels: name: Name
	}
}

Deployment: [Name=string]: {
	apiVersion: "apps/v1"
	kind:       "Deployment"
	metadata: {
		name: Name
		labels: app: Name
	}
	spec: {
		selector: matchLabels: app: Name
		template: metadata: labels: app: Name
	}
}
EOF

cue trim -s ./simple

cue export ./simple

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./simple | kubectl apply -f -

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./simple | kubectl delete -f -

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

Multiple Configurations

cue import -l 'kind' -l 'metadata.name' -p demo -f ./multi

cue trim -s ./multi

cat > multi/multi.cue <<EOF
package demo

Deployment: [_]: spec: template: spec: containers: [{
	name:  "nginx"
	image: "nginx"
	ports: [{
		containerPort: 80
	}]
}]
EOF

cue trim -s ./multi

cue export ./multi

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./multi | kubectl apply -f -

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./multi | kubectl delete -f -

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

Tiered Configuration

cue import -l 'kind' -l 'metadata.name' -p demo -f ./org/**/*.yaml

cue trim -s ./org/*/*/

cat > org/org.cue <<EOF
package demo

Deployment: [_]: spec: template: spec: containers: [{
	name:  "nginx"
	image: "nginx"
	ports: [{
		containerPort: 80
	}]
}]
EOF

cue trim -s ./org/*/*/

cat >> org/org.cue <<EOF

_org: string | *"org"

_dept: string | *"none"

_org_dept: "\(_org)-\(_dept)"

_ns: "ns-\(_org_dept)"

_app: "app-\(_org_dept)"

_env: *"scratch" | "dev" | "qa" | "prod"

Namespace: "\(_ns)": {}

Namespace: [_]: metadata: name: _ns

Deployment: "\(_app)": {}

Deployment: [_]: metadata: namespace: _ns

Deployment: [_]: metadata: name: _app

Namespace: [_]: metadata: labels: environment: _env
Deployment: [_]: {
	metadata: labels: environment: _env
	spec: {
		selector: matchLabels: environment: _env
		template: metadata: labels: environment: _env
	}
}
EOF

# This will throw some errors, but it highlights what we need to do
cue trim -s ./org/*/*/

cat >org/dept-a/dept-a.cue <<EOF
package demo

_dept: "dept-a"
EOF

cat >org/dept-b/dept-b.cue <<EOF
package demo

_dept: "dept-b"
EOF

cue trim -s ./org/*/*/

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./org/dept-a/dev | kubectl apply -f -

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./org/dept-a/dev | kubectl delete -f -

for d in dept-a dept-b; do
  for e in dev prod; do
    cat >>org/$d/$e/*.cue <<EOF
_env: "$e"
EOF
  done
done

cue trim -s ./org/*/*/

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./org/dept-a/dev | kubectl apply -f -

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./org/dept-a/dev | kubectl delete -f -

for d in dept-a dept-b; do
  for e in dev prod; do
    cat >org/$d/$e/*.cue <<EOF
package demo

_env: "$e"
EOF
  done
done

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./org/dept-a/dev | kubectl apply -f -

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

kubectl describe deployment app-org-dept-a -n ns-org-dept-a

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./org/dept-a/dev | kubectl delete -f -

CUE Scripting

cat >demo_tool.cue <<EOF
package demo

import (
    "encoding/json"
    "tool/cli"
)

command: demo: cli.Print & {
    out: {
        apiVersion: "v1"
        kind: "List"
        items: [for x in [Namespace, Deployment] for y in x {y}]
    }
    text: json.Marshal(out)
}
EOF

cue cmd demo ./org/dept-a/dev

cue cmd demo ./org/dept-a/dev | jq

cue cmd demo ./org/dept-a/dev | kubectl apply -f -

kubectl get all -A --field-selector metadata.namespace!=kube-system,metadata.namespace!=default

cue cmd demo ./org/dept-a/dev | kubectl delete -f -

Random Bits

Import YAML

cue import -l 'kind' -l 'metadata.name' -l '"k8s"' -p demo --dryrun -f -o ./simple/nginx-k8s.cue ./simple

Export K8S Configuration

cue export -e Namespace ./simple

cue export -e '[Namespace, Deployment]' ./simple

cue export -e '[for x in [Namespace, Deployment] {x}]' ./simple

cue export -e '[for x in [Namespace, Deployment] for y in x {y}]' ./simple

cue export -e '{"apiVersion": "v1", "kind": "List", "items": [for x in [Namespace, Deployment] for y in x {y}]}' ./simple

References

• https://cuelang.org/
• https://github.com/cue-lang/cue
• https://cuetorials.com/
• A Practical guide to CUE: patterns of everyday use
  • https://github.com/cue-examples/fosdem2022
• https://engineering.mercari.com/en/blog/entry/20220127-kubernetes-configuration-management-with-cue/
• https://engineering.mercari.com/en/blog/entry/20220122-adventures-of-using-cue-at-scale/
• https://www.alibabacloud.com/blog/configure-a-new-capability-for-kubernetes-paas-in-20-minutes_597277
• https://bitfieldconsulting.com/golang/cuelang-exciting
• https://github.com/thesecuresoftwarefactory/ssf