I manually update the DNS settings at the registrar for my domains, such as

    https://domains.google.com/registrar

What are people using to automate updates to DNS settings? which registrars have an API ?

Specifically I need to manually update : 

- TXT field for the DKIM setting

- TXT field for spf  

    @                  TXT          1m       "v=spf1 ip4:100.22.22.100 include:blah.com -all"

- A record everytime I change external IP

To run my own DNS host servers seems like overkill. Ideally I would just make some secure REST call to perform programmatic updates.