Lynq
GitHub stars

Template Syntax Reference ​

Complete reference for template variables, custom functions, the Sprig library, and advanced techniques.

Related pages

Available Variables ​

Required Variables ​

These are always available from the template context:

yaml
.uid         # Node unique identifier (from uid mapping)
.activate    # Activation status (from activate mapping)

Context Variables ​

Automatically provided:

yaml
.hubId        # LynqHub name
.templateRef  # LynqForm name

Custom Variables ​

From extraValueMappings in LynqHub:

yaml
spec:
  extraValueMappings:
    planId: subscription_plan
    region: deployment_region
    dbHost: database_host

Access in templates:

yaml
.planId   # Maps to subscription_plan column
.region   # Maps to deployment_region column
.dbHost   # Maps to database_host column

Deprecated Variables ​

DEPRECATED

The following variables are deprecated since v1.1.11 and will be removed in v1.3.0:

yaml
.hostOrUrl   # Original URL/host from hub (from hostOrUrl mapping)
.host        # Auto-extracted host from .hostOrUrl

Migration: Use extraValueMappings + the toHost() function instead. See Debugging & Migration.

Built-in Custom Functions ​

toHost(url) ​

Extract hostname from URL:

yaml
# Input: https://acme.example.com:8080/path
# Output: acme.example.com
env:
- name: HOST
  value: "{{ .domainUrl | toHost }}"  # Use with extraValueMappings

trunc63(s) ​

Truncate to 63 characters (Kubernetes name limit):

yaml
nameTemplate: "{{ printf \"%s-%s-deployment\" .uid .region | trunc63 }}"

sha1sum(s) ​

Generate SHA1 hash — useful for short, stable, unique resource names:

yaml
nameTemplate: "app-{{ .uid | sha1sum | trunc 8 }}"

fromJson(s) ​

Parse JSON string from a database column:

yaml
# Database column: config = '{"apiKey":"sk-abc","endpoint":"https://api.example.com"}'
env:
- name: API_KEY
  value: "{{ (.config | fromJson).apiKey }}"
- name: ENDPOINT
  value: "{{ (.config | fromJson).endpoint }}"

Sprig Functions (200+) ​

Full documentation: https://masterminds.github.io/sprig/

String Functions ​

yaml
nameTemplate: "{{ .uid | upper }}"
nameTemplate: "{{ .uid | lower }}"
value: "{{ .name | trim }}"
value: "{{ .uid | replace \".\" \"-\" }}"
value: "{{ .name | quote }}"

Encoding Functions ​

yaml
value: "{{ .secret | b64enc }}"
value: "{{ .encoded | b64dec }}"
value: "{{ .param | urlquery }}"
value: "{{ .data | sha256sum }}"

Default Values ​

yaml
image: "{{ .deployImage | default \"nginx:stable\" }}"
port: "{{ .appPort | default \"8080\" }}"
region: "{{ .region | default \"us-east-1\" }}"

Conditionals ​

Prefer ternary for binary switches — it stays on one line and reads left-to-right:

yaml
# ternary vTrue vFalse condition
env:
- name: DEBUG
  value: "{{ ternary \"true\" \"false\" (eq .planId \"enterprise\") }}"
replicas: {{ ternary 5 2 (eq .planId "enterprise") | int }}

Use if/else when constructing strings from multiple variables or when the condition is compound:

yaml
- name: HOST
  value: "{{ if and .customDomain (eq .domainVerified \"true\") }}{{ .customDomain }}{{ else }}{{ .uid }}.default.svc{{ end }}"

Lists and Iteration ​

yaml
annotations:
  tags: "{{ list \"app\" .uid .region | join \",\" }}"

Math Functions ​

yaml
value: "{{ add .basePort 1000 }}"
value: "{{ mul .cpuLimit 2 }}"
value: "{{ max .minReplicas 3 }}"

Template Rendering Process ​

1. Variable Collection ​

The hub controller collects variables from the database row and merges them with context:

uid       = "acme-corp"
activate  = true
planId    = "enterprise"           # from extraValueMappings
domainUrl = "https://acme.ex.com"  # from extraValueMappings
hubId     = "customer-hub"         # context
templateRef = "customer-web-app"   # context

2. Template Evaluation ​

For each resource in the LynqForm:

  1. Render nameTemplate → resource name
  2. Render labelsTemplate → labels map
  3. Render annotationsTemplate → annotations map
  4. Render spec → recursively render all string values

3. Resource Application ​

The rendered resource is applied to Kubernetes using Server-Side Apply with fieldManager: lynq.

Advanced Template Techniques ​

Local Variables ​

Define a local variable to avoid repeating complex expressions:

yaml
nameTemplate: |
  {{- $base := printf "%s-%s" .uid (.region | default "default") -}}
  {{ $base | trunc63 }}-web

Multi-Tier with Shared Variable ​

yaml
deployments:
  - id: web
    nameTemplate: |
      {{- $base := printf "%s-%s" .uid (.region | default "default") -}}
      {{ $base | trunc63 }}-web
    spec:
      apiVersion: apps/v1
      kind: Deployment
      spec:
        replicas: "{{ .webReplicas | default \"2\" | int }}"
        template:
          spec:
            containers:
              - name: web
                image: "{{ .webImage | default \"nginx:stable\" }}"
                env:
                  {{- $apiHost := printf "%s-api-svc.%s.svc.cluster.local" .uid .namespace }}
                  - name: API_ENDPOINT
                    value: "http://{{ $apiHost }}"
  - id: api
    nameTemplate: |
      {{- $base := printf "%s-%s" .uid (.region | default "default") -}}
      {{ $base | trunc63 }}-api
    dependIds: [web]
    spec:
      apiVersion: apps/v1
      kind: Deployment
      spec:
        replicas: "{{ .apiReplicas | default \"3\" | int }}"
        template:
          spec:
            containers:
              - name: api
                image: "{{ .apiImage | default \"api:latest\" }}"
                env:
                  {{- $dbHost := printf "%s-db.%s.svc.cluster.local" .uid .namespace }}
                  - name: DATABASE_URL
                    value: "postgres://{{ $dbHost }}:5432/{{ .uid }}"

Range Over Lists ​

yaml
data:
  endpoints.txt: |
    {{- range $i, $region := list "us-east-1" "us-west-2" "eu-west-1" }}
    {{ $region }}.example.com
    {{- end }}

Complex JSON Parsing ​

yaml
# Database column: config = '{"db":{"host":"localhost","port":5432}}'
env:
- name: DB_HOST
  value: "{{ ((.config | fromJson).db).host }}"
- name: DB_PORT
  value: "{{ ((.config | fromJson).db).port }}"

See Also ​