Today, we had an issue with connecting to Kadira mostly from apps hosted at modulus. But it turns out that, it's not a modulus problem but a problem on the AWS DNS resolver. It couldn't identify kadira's DNS entry which is engine.kadira.io.
So, we've added another DNS entry point for kadira called enginex.kadira.io and it'll fix the issue.
Since this is an AWS issue, this affects most of the Kadira deployments including apps hosted on
*.meteor.com, modulus and heroku.
How to get the fix