Question 27026 in CentOS Question posted in
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Pods can't resolve external DNS – CentOS

I have a problem with k8s hosted on my own bare-metal infrastructure.

The k8s was installed via kubeadm init without special configuration, and then I apply CNI plugin

Everything works perfectly expects external DNS resolution from Pod to the external world (internet).

For example:

I have Pod with the name foo, if I invoke command curl google.com I receive error
curl: (6) Could not resolve host: google.com

but if I invoke the same command on the same pod a second time I receive properly HTML

<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<TITLE>301 Moved</TITLE></HEAD><BODY>
<H1>301 Moved</H1>
The document has moved
<A HREF="http://www.google.com/">here</A>.
</BODY></HTML>

and if I repeat this command again I can receive errors with DNS resolution or HTML and so on.
this behavior is random sometimes I must hit 10times and get an error and on 11 hits I can receive Html

I also try to debug this error with this guide, but it does not help.

Additional information:
CoreDNS is up and running and have default config

apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health {
           lameduck 5s
        }
        ready
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           fallthrough in-addr.arpa ip6.arpa
           ttl 30
        }
        prometheus :9153
        forward . /etc/resolv.conf {
           max_concurrent 1000
        }
        cache 30
        loop
        reload
        loadbalance
    }
kind: ConfigMap
metadata:
  name: coredns

and files /etc/resolv.conf looks fine

nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local 
options ndots:5

the problem exists on Centos 8(master, kubeadm init) and on Debian 10(node, kubeadm join)
SELinux in on permissive and SWAP is disabled

it is looks like after install k8s and weavenet problem appear even on the host machine.

I’m not certain where the problem came from either k8s or Linux.
It started after I have installed k8s.

what have I missed?

Tags:

2

Answers


  1. 0

    I can suggest using different CNI plugin and setting it up from scratch. Remember when using kubeadm , apply CNI plugin after you ran kubeadm init, then add worker nodes. Here you can find supported CNI plugins. If the problem still exists, it’s probably within your OS.

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  2. 0

    Check /etc/resolv.conf. The conf file can set the nameserver to 8.8.8.8.

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