I've made a Heroku NodeJS app. At first time, it had "web" type of app. I setup New Relic so the app won't shutdown. New Relic pings the app by https protocol.
I changed the app to "worker" type, then New Relic responded with 503 status code, so ping operations are all failed. How to ping a "worker" Heroku app to keep it alive?
You cannot. The worker process will not listen on any HTTP port.
You shouldn't need it either. If you don't have any web dynos, your worker will not sleep.
If you have a web dyno, the worker will be put to sleep when the web goes to sleep. So adding a ping to the web dyno would be enough.
See https://devcenter.heroku.com/articles/free-dyno-hours#dyno-sleeping
