Adding a Custom DNS Entry to CoreDNS

I ran into a small problem recently when I was leveraging my site updating code referenced in Automating Static WordPress Updates. The problem was that I was unable to update content reliably for two reasons:

1. The content was not properly switching out the hostname in the URL when I would crawl my backend WordPress site. I actually implemented something that helped to correct this but it lead to problem #2. I should probably post a new article on the changes I made in my script…
2. My script would only crawl the external static site so updates were not getting published. This lead me to creating this post!

Now that I have the problems covered, let’s get right to it. In order to resolve the issue, I needed my Kubernetes to have split DNS for certain hosts. I needed my static site updating script to be able to crawl my backend WordPress and NOT crawl the public facing static site.

Edit coreDNS’s configmap

In order to add a custom entry to your Kubernetes, you can simply edit coredns’s configmap and add a new hosts entry. Here is my current coredns configmap:

apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health
        ready
        kubernetes cluster.local in-addr.arpa ip6.arpa {
          pods insecure
          fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        forward . /etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
        import custom/*.override
    }
    import custom/*.server
kind: ConfigMap

Based upon the hosts information provided by CoreDNS, we just add a new host block and life will be good, right? I noticed that in the documentation, I see This plugin only supports A, AAAA, and PTR records. That’s not going to work since I’m wanting to point to a new hostname. Instead, we’ll use the rewrite syntax. Below is my updated CoreDNS configmap.

apiVersion: v1
data:
  Corefile: ".:53 {
    errors
    health
    rewrite stop {
       name exact live-blog.shellnetsecurity.com. nginx-npp.wordpress.svc.cluster.local
       answer name nginx-npp.wordpress.svc.cluster.local. live-blog.shellnetsecurity.com
    }   
    ready
    kubernetes cluster.local in-addr.arpa ip6.arpa {
      pods insecure
      fallthrough in-addr.arpa ip6.arpa
    }
    prometheus :9153
    forward . /etc/resolv.conf
    cache 30
    loop
    reload
    loadbalance
    import
    custom/*.override
  }
  import custom/*.server"
kind: ConfigMap

Fixed and no restart required like with using hosts