kubernetes/kops · error

unable to unmarshall content from template: %s, error: %s

Error message

unable to unmarshall content from template: %s, error: %s

What it means

Returned by RunToolBoxTemplate when a rendered template document fails yaml.Unmarshal into map[string]interface{} during --format-yAML processing. After rendering, the output is split on "---\n" and each chunk must be a YAML mapping; invalid YAML syntax, non-mapping documents (scalars/lists), or template artifacts that render to garbage trigger this error. The failing chunk is embedded verbatim in the message.

Source

Thrown at cmd/kops/toolbox_template.go:199

		rendered, err := r.Render(string(content), context, snippets, options.failOnMissing)
		if err != nil {
			return fmt.Errorf("unable to render template: %s, error: %s", x, err)
		}
		// @check if the content is zero ignore it
		if len(rendered) <= 0 {
			continue
		}

		if !options.formatYAML {
			documents = append(documents, strings.Split(rendered, "---\n")...)
			continue
		}

		for _, x := range strings.Split(rendered, "---\n") {
			var data map[string]interface{}
			if err := yaml.Unmarshal([]byte(x), &data); err != nil {
				return fmt.Errorf("unable to unmarshall content from template: %s, error: %s", x, err)
			}
			if len(data) <= 0 {
				continue
			}
			formatted, err := yaml.Marshal(&data)
			if err != nil {
				return fmt.Errorf("unable to marhshal formatted content to yaml: %s", err)
			}
			documents = append(documents, string(formatted))
		}
	}
	// join in harmony all the YAML documents back together
	content := strings.Join(documents, "---\n")

	iowriter := out
	// @check if we are writing to a file rather than stdout
	if options.outputPath != "" {
		w, err := os.OpenFile(utils.ExpandPath(options.outputPath), os.O_RDWR|os.O_TRUNC|os.O_CREATE, 0o660)

View on GitHub (pinned to 4c8573c808)

Solutions

1. Read the offending chunk in the error message and fix the YAML syntax at that point (indentation with spaces, quote strings containing : or #)
2. Ensure each document between --- separators is a YAML mapping (key: value), not a scalar or list
3. Quote values substituted into the template if they may contain YAML special characters
4. Temporarily drop --format-yAML to see the raw rendered output and diagnose what the substitution produced
5. Validate the rendered output with a linter such as yamllint

Example fix

// before (rendered doc)
metadata:
	name: my-cluster

// after
metadata:
  name: my-cluster

for _, doc := range strings.Split(rendered, "---\n") {
    var m map[string]interface{}
    if err := yaml.Unmarshal([]byte(doc), &m); err != nil {
        return fmt.Errorf("rendered chunk is not a YAML mapping: %v", err)
    }
}

func isYAMLMapping(doc string) bool {
    var m map[string]interface{}
    return yaml.Unmarshal([]byte(doc), &m) == nil
}

if err := yaml.Unmarshal([]byte(doc), &data); err != nil {
    return fmt.Errorf("document %q is not a YAML mapping (check tabs, unquoted special chars): %w", doc, err)
}

When it happens

Trigger: --format-yAML is used and a rendered document chunk contains invalid YAML (tabs for indentation, duplicate keys, bad escapes) or is a non-mapping (a bare scalar, a list at top level), including chunks where the template rendered unexpected content between --- separators.

Common situations: Rendered values injecting special characters (colons in unquoted strings, "#" starting comments) that break YAML; tab indentation introduced by values substitution; templates whose sections between --- render to empty-but-nonempty whitespace or scalar output; assuming formatYAML can reformat non-map documents.

Related errors

• error parsing channel %q: %v
• error parsing configuration: %v
• failed to parse manifest: %w
• error parsing addons or manifest: %v
• error parsing addons: %v

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/bf2463725568391e. Report an issue: GitHub.