Environment Variables used by Meteor

BIND IP: bind to a specific IP address (optional)
DISABLE WEBSOCKETS: Set to 1 to disable trying websockets first before falling back to sockjs emulation
HTTP_FORWARDED_COUNT: set this with the number of proxies Meteor is running behind (optional)
MAIL_URL: how Meteor will send email, SMTP settings etc. (required to send email)
METEOR_SETTINGS: various runtime settings, see link (optional)
MONGO_OPLOG_URL: URL for Mongo (optional)
MONGO_URL: URL for connecting to Mongo (required in production)
NODE_ENV: not required by Meteor but set to ‘PRODUCTION’ by most node.js PaaS providers.
NODE_OPTIONS: Used in development (i.e. via Meteor-run) to pass additional options to node (like –debug). Optional.
PACKAGE_DIRS: If you wish to add packages outside of your application folder structure, set it to directory containing the packages. If more than one location, use colon to delimit the list. (optional)
PORT: What port to listen on (optional, defaults to 3000)
ROOT_URL: Default URL for how your app should be access (required on production)

Setting ROOT_URL in C9 fixes issues with Google login redirection.