In MacOS, please consider changing the Docker command to use /private instead of /var. "/private/var" is an alias to "/var" and is by default exported to Docker i MacOS. To get node-lambda to work, I had to remove the default value of "/private" and replace it with "/var/folders". This is because Docker (8.x) won't let you have both because they are considered the same.

Solution: Since the tmp folder path is probably auto generated, you might need to just prepend "/private" to the path, if the OS is MacOS.

Here's more info on the subject:
https://stackoverflow.com/questions/45122459/docker-mounts-denied-the-paths-are-not-shared-from-os-x-and-are-not-known