What is the syntax of annotation values in Kubernetes?

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According to Kubernetes documentation

The metadata in an annotation can be small or large, structured or unstructured, and can include characters not permitted by labels.

Annotations, like labels, are key/value maps

Then there is a detailed explanation on the syntax of the annotation keys. But it says nothing about the value part.

Where can I find more about the allowed length and character set for the value of an annotation in Kubernetes?

kubernetes
1 Answers

Here you can find the code that validates annotations in current master:

func ValidateAnnotations(annotations map[string]string, fldPath *field.Path) field.ErrorList {
    allErrs := field.ErrorList{}
    for k := range annotations {
        for _, msg := range validation.IsQualifiedName(strings.ToLower(k)) {
            allErrs = append(allErrs, field.Invalid(fldPath, k, msg))
        }
    }
    if err := ValidateAnnotationsSize(annotations); err != nil {
        allErrs = append(allErrs, field.TooLong(fldPath, "", TotalAnnotationSizeLimitB))
    }
    return allErrs
}

The keys are validated according to the rules that you mentioned. The only validation applied to the values is the total length of all annotations (size of keys + size of values for all annotations) that can't be longer than 256Kb.

const TotalAnnotationSizeLimitB int = 256 * (1 << 10) // 256 kB

...

func ValidateAnnotationsSize(annotations map[string]string) error {
    var totalSize int64
    for k, v := range annotations {
        totalSize += (int64)(len(k)) + (int64)(len(v))
    }
    if totalSize > (int64)(TotalAnnotationSizeLimitB) {
        return fmt.Errorf("annotations size %d is larger than limit %d", totalSize, TotalAnnotationSizeLimitB)
    }
    return nil
}
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