Set Node.js Environment Variable (NODE_ENV) in iisnode to Production/Development/Test

Joachim is right above that adding <iisnode node_env="production" /> to web.config allows control over the NODE_ENV value. Another way is to add the iisnode.yml file next to your web.config, and in there spcify the NODE_ENV value as node_env: production. See other settings you can use in iisnode.yml at https://github.com/tjanczuk/iisnode/blob/master/src/samples/configuration/iisnode.yml