• Java: JVM DNS cache settings

    2 min read

    One of the annoyances of running workloads in a JVM is taking into account that it has it's own DNS cache: It's easy to forgot about it when troubleshooting an issue so we might end up not understanding the problem at all

    11/05/2022

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  • Pod and Service DNS naming schema

    2 min read

    kubernetes DNS name resolution

    Kubernetes provides a DNS to be used to locate other pods or services instead of using it's IP address. The default cluster domain is cluster.local but we can change it if we like.

    18/06/2021

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  • Troubleshoot Kubernetes service not being resolved

    2 min read

    When you create a Kubernetes Service, pods from within the same namespace should be able to resolve it's IP by name. For example, if we create a service named ampa-votacions; any pod from the same namespace should be able to resolve it's IP. But sometimes it can't be resolved:

    $ kubectl exec -it ampa-install-ws7cw -- sh
    / $ nslookup ampa-votacions
    Server:   172.20.0.10
    Address:  172.20.0.10:53
    
    ** server can't find ampa-votacions.us-west-2.compute.internal: NXDOMAIN
    
    ** server can't find ampa-votacions.ampa.svc.cluster.local: NXDOMAIN
    
    ** server can't find ampa-votacions.svc.cluster.local: NXDOMAIN
    
    ** server can't find ampa-votacions.ampa.svc.cluster.local: NXDOMAIN
    
    ** server can't find ampa-votacions.cluster.local: NXDOMAIN
    
    ** server can't find ampa-votacions.svc.cluster.local: NXDOMAIN
    
    ** server can't find ampa-votacions.cluster.local: NXDOMAIN
    
    ** server can't find ampa-votacions.us-west-2.compute.internal: NXDOMAIN
    

    19/04/2021

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  • tcpdump: filter DNS queries

    2 min read

    When a DNS change is involved in an ongoing issue, we need to be sure when we use, for example curl, whether we are hitting the new or the old resource. Is that DNS record still cached locally? One of the best ways of checking this is by sniffing the DNS traffic using tcpdump

    30/03/2021

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From pet to cattle
Treat your kubernetes clusters like cattle, not pets