variable "image_metadata" { default = { key: "value", something: { foo: "bar", } } validation { condition = length(var.image_metadata.key) > 4 error_message = "The image_metadata.key field must be more than 4 runes." } validation { condition = substr(var.image_metadata.something.foo, 0, 3) == "bar" error_message = "The image_metadata.something.foo field must start with \"bar\"." } }