I ran into exactly this issue for the cert-manager to obtain a LetsEncrypt certificate for our cluster. (The ACME URL was failing inside the pod: no route to host). It took me quite a long time just to figure out it was a DNS related issue because K8s buries technology behind so many layers. How can I make a simple edit to /etc/hosts? Who knows? Ohh and you are not supposed to do it that way anyway. The solution ended up being forcing the cert-manger to run on a node with no DNS issues using such Byzantine terms as "tolerations". Its that bizarre vocabulary where they are obviously trying really hard to abstract something away from you that you would just rather be able to get your hands on. It reminds me of other absurdly complex technologies from the Java world like J2EE and whatnot.