If Mongo DB gets down after Meteor app is up and running then how I can check that it’s down or not?
I think you could set a Monti (https://montiapm.com/) alert for long running queries or methods.
If you host with Atlas, you could add an alert for the number of connections:
We have local version of app not connected to the Internet. I can see debug messages Exception while polling query. So the question if there any hook or callback or anything to get informed that DB is down.
some of the Mongo options have changed since but this is a good start I think: Exception while polling query (QUERY): MongoError: connection (NUMBER) to (MONGODB) closed · Issue #9135 · meteor/meteor · GitHub
In my case mongo is really down. Just want to catch such cases and show windows with error message.