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Red Cricket
Asked: 2021-08-17 13:40:26 +0800 CST

why is ssh using cached dns record when dig reports updated version of cname record?

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I have a Jenkins pipeline that will start my AWS Ubuntu EC2 instances. This Jenkins pipeline will also update a CNAME record I have for my EC2 instances in route53.

Sometimes there is a long delay in my ability to ssh to the instance via the CNAME. I figured it might be a cache issue, but if I execute dig the-cname.example.com I see the updated versions of the DNS records. Also I have no problem ssh'ing to the new IP and the value of the DNS A record that AWS gave my instance.

Is my ssh client using a cached version of the CNAME?

domain-name-system ssh

1 Answers

  1. Best Answer

    dig performs an actual DNS query, while ssh will simply ask your system (most likely through gethostbyname) to resolve a name.

    dig will ask an actual DNS server while ssh will ask the local service in charge of DNS (nowadays, most likely systemd-resolve) which will cache results.

    If using systemd, you can clear the cash using systemd-resolve flush-caches.

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