hashicorp/terraform · error

lookup failed to find key

Error message

lookup failed to find key %s

What it means

lookup() runtime error: the requested key was not present in the map/object and no default value was supplied. The function searches object attributes and map keys; if HasIndex/HasAttribute is false and defaultValueSet is false, it returns this error. The key is passed through redactIfSensitive so sensitive keys are not leaked.

Solutions

1. Add a third argument as the default: lookup(var.map, "key", "fallback").
2. Ensure the key actually exists (use contains/keys to check first).
3. Rename the key in the lookup to match the current map.

Example fix

// before
name = lookup(var.tags, "Name")

// after
name = lookup(var.tags, "Name", "default-name")

// Always provide a default, or check contains() first.
locals {
  name = contains(keys(var.map), var.key) ? lookup(var.map, var.key) : "fallback"
}

When it happens

Trigger: lookup(map, key) where key does not exist in map and the third (default) argument is omitted; or lookup on an object whose attribute name is missing.

Common situations: Map keys sourced from a variable/list where a specific key isn't always present, environment-specific data missing an entry, refactor that renamed a key but callers weren't updated.

Related errors

• lookup() takes two or three arguments, got
• invalid CIDR expression
• at most 1 action can be invoked per operation
• can't compute sum of opposing infinities
• can't delete default state

AI-assisted analysis of hashicorp/terraform@d32a084675 (2026-08-11). Data as JSON: /api/errors/6cd297cf2ecf08a7. Report an issue: GitHub.

Appendix: source

Thrown at internal/lang/funcs/collection.go:326

		lookupKey := keyVal.AsString()

		if mapVar.Type().IsObjectType() {
			if mapVar.Type().HasAttribute(lookupKey) {
				return mapVar.GetAttr(lookupKey).WithMarks(markses...), nil
			}
		} else if mapVar.HasIndex(cty.StringVal(lookupKey)) == cty.True {
			return mapVar.Index(cty.StringVal(lookupKey)).WithMarks(markses...), nil
		}

		if defaultValueSet {
			defaultVal, err = convert.Convert(defaultVal, retType)
			if err != nil {
				return cty.NilVal, err
			}
			return defaultVal.WithMarks(markses...), nil
		}

		return cty.UnknownVal(cty.DynamicPseudoType), fmt.Errorf(
			"lookup failed to find key %s", redactIfSensitive(lookupKey, keyMarks))
	},
})

// MatchkeysFunc constructs a function that constructs a new list by taking a
// subset of elements from one list whose indexes match the corresponding
// indexes of values in another list.
var MatchkeysFunc = function.New(&function.Spec{
	Params: []function.Parameter{
		{
			Name: "values",
			Type: cty.List(cty.DynamicPseudoType),
		},
		{
			Name: "keys",
			Type: cty.List(cty.DynamicPseudoType),
		},
		{

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