Kong: Name resolution failed

Sometimes when calling a service on kong you might get a response like this

HTTP/1.1 503 Service Temporarily Unavailable
Connection: keep-alive
Content-Length: 36
Content-Type: application/json; charset=utf-8
Date: Thu, 02 Apr 2020 09:28:06 GMT
Server: kong/2.0.1
X-Kong-Response-Latency: 12

    "message": "name resolution failed"

What does it mean?

Kong cannot access the upstream

Make sure the corret protocol http or https is used.
Also if the upstream's SSL cannot be verified then