Cisco Umbrella is blocking my Node.js App in Heroku website?
Cisco Umbrella will block sites it deems to be a Security Threat to help protect people accessing these sites. This is normally because the site has been associated with one of three activities: malware, phishing, or command and control. If the domain is new then Cisco Umbrella has an option to block new domains for a period of time to protect users against temporary malicious domains.
This protection is achieved when using Cisco Umbrella as a DNS resolvee. This is either done using a client on your device or as a network configuration.
If your certain the domain is safe, you can whitelistthe dmain via the Umbrella Dashboard, if available. Alternativly use another DNS resolver services such as Google which offers no protection or filtering.