I am trying to understand what exactly the function "lookup" does in terraform code? does it find maps or lists? just confused how to use this lookup correctly.
11 Answer
The lookup documentation has the following to say about it:
lookupretrieves the value of a single element from a map, given its key. If the given key does not exist, the given default value is returned instead.
The normal way to look up a value from a map by key is to use the index syntax, like example["foo"], but that operation will return an error if there is no element with the key foo in the map example.
lookup is therefore similar to the index syntax except for the additional behavior of choosing a fallback value to use instead of an error if the key doesn't exist. lookup(example, "foo", "default") is the same as example["foo"] except that it will produce "default" rather than an error if there is no element with the key "foo".
More recent Terraform versions also have the try function which can serve as a perhaps easier to understand alternative to lookup, because it still uses the normal index syntax as part of the expression: try(example["foo"], "default") is similar to lookup(example, "foo", "default"), and will produce the same result as long as example is a map of strings.
