Template Type Conversion

^1.1.15

How to produce correctly-typed integers, floats, and booleans in Lynq templates.

Related pages

• Templates Overview — Quick start
• Template Syntax Reference — Variables and functions

The YAML Quoting Problem

When writing LynqForm CRDs in YAML, template expressions must be quoted because the YAML parser requires it:

# INVALID YAML — parser error
containerPort: {{ .appPort }}

# Valid YAML — must quote template expressions
containerPort: "{{ .appPort }}"

The problem: Quotes make the YAML valid, but the rendered output remains a string, causing Kubernetes API validation to fail for numeric and boolean fields:

# After rendering without type functions
containerPort: "8080"  # Kubernetes rejects — expected integer
replicas: "3"          # Kubernetes rejects — expected integer
enabled: "true"        # Kubernetes rejects — expected boolean

# What Kubernetes expects
containerPort: 8080    # integer
replicas: 3            # integer
enabled: true          # boolean

---

Type Conversion Functions

int(value)

Convert to integer:

replicas: "{{ .maxReplicas | int }}"                   # "3" → 3
containerPort: "{{ .appPort | int }}"                  # "8080" → 8080
replicas: "{{ .replicas | default \"2\" | int }}"      # chain with default
value: "{{ .cpuCount | int }}"                         # 2.8 → 2 (truncates)

Conversion rules:

• String "123" → 123
• Float 2.8 → 2 (truncates)
• Already int → returns as-is
• Invalid input → 0 (graceful fallback)

float(value)

Convert to float64:

resources:
  limits:
    cpu: "{{ .cpuLimit | float }}"              # "1.5" → 1.5
targetCPUUtilization: "{{ .threshold | float }}" # "75.5" → 75.5

Conversion rules:

• String "1.5" → 1.5
• Int 2 → 2.0
• Already float → returns as-is
• Invalid input → 0.0

bool(value)

Convert to boolean:

enabled: "{{ .featureEnabled | bool }}"                     # "true" → true
readOnly: "{{ .isReadOnly | bool }}"                        # "false" → false
automountServiceAccountToken: "{{ .autoMount | bool }}"    # 1 → true, 0 → false

Truthy values → true:

• Strings: "true", "True", "TRUE", "1", "yes", "Yes", "YES", "y", "Y"
• Numbers: any non-zero integer (1, 42, -5)
• Boolean: true

Falsy values → false:

• Strings: "false", "False", "FALSE", "0", "no", "No", "NO", "n", "N", "" (empty)
• Numbers: 0
• Boolean: false

---

When to Use Type Conversion

Use type conversion for

• Integers: replicas, containerPort, targetPort, minReplicas, maxReplicas
• Floats: cpu resource limits/requests, targetCPUUtilizationPercentage
• Booleans: automountServiceAccountToken, readOnlyRootFilesystem, privileged

Don't use type conversion for

• Environment variable values — always strings in containers
• Labels and annotations — always strings
• Command arguments — always strings
• ConfigMap/Secret data values — always strings
• Image tags — always strings even if numeric-looking ("1.2.3")

---

Complete Example

apiVersion: operator.lynq.sh/v1
kind: LynqForm
metadata:
  name: typed-app
spec:
  hubId: production-db
  deployments:
    - id: app
      nameTemplate: "{{ .uid }}-api"
      spec:
        apiVersion: apps/v1
        kind: Deployment
        spec:
          replicas: "{{ .maxReplicas | default \"2\" | int }}"
          template:
            spec:
              automountServiceAccountToken: "{{ .mountToken | bool }}"
              containers:
                - name: app
                  image: "{{ .image }}"
                  ports:
                    - containerPort: "{{ .appPort | int }}"
                      protocol: TCP
                  env:
                    # String fields — no conversion needed
                    - name: APP_ENV
                      value: "{{ .environment }}"
                    - name: NODE_ID
                      value: "{{ .uid }}"
                    # Integer env var — keep as string (env values are always strings)
                    - name: MAX_CONNECTIONS
                      value: "{{ .maxConns }}"
                  resources:
                    limits:
                      cpu: "{{ .cpuLimit | float }}"
                      memory: "{{ .memoryLimit }}Mi"
                    requests:
                      cpu: "{{ .cpuRequest | float }}"
                      memory: "{{ .memoryRequest }}Mi"

---

How It Works

The int/float/bool functions use type markers internally to survive the template rendering boundary:

1. Template function wraps the result:

   int("42") → "__LYNQ_TYPE_INT__42"  // internal representation

2. Go template engine processes normally — the marker is treated as a string and survives evaluation.

3. Controller detects and restores the type:

   renderUnstructured() detects marker → converts to native Go int → 42

4. Kubernetes receives a correctly-typed value:

   containerPort: 42  # pure integer, no quotes

Why not use Sprig's atoi?

Go's text/template engine always returns rendered results as strings, regardless of what type a function returns internally. Sprig's atoi returns an integer during template execution, but the final output is still a string.

The type marker approach is the only way to preserve type information across the template rendering boundary.

See Also

• Template Syntax Reference — All variables and functions
• Debugging & Migration — Type-related error messages and fixes