support TTL derived from zone

[szuecs]

We should omit setting default TTLs and usethe default from the derived SOA records.
I would hope that all APIs are ok with not specifying a TTL, while creating a DNS record and it will derive the ttl from the origin config.

As I see google DNS is ok with specifying TTL=0, omitwhich probably means "omit cache". So TTL=0 can not be used in the API calls.

[stealthybox]

I'm noticing that when I modified the Google Provider to not pass a TTL, Cloud DNS did not use the MINIMUM =300 value in the non RFC compliant way: (resulted in 0 instead of 300)

❯ gcloud dns record-sets list --zone companyci-com
NAME                   TYPE  TTL    DATA
companyci.com.        NS    21600  ns-cloud-c1.googledomains.com.,ns-cloud-c2.googledomains.com.,ns-cloud-c3.googledomains.com.,ns-cloud-c4.googledomains.com.
companyci.com.        SOA   21600  ns-cloud-c1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 259200 300
nginx.companyci.com.  A     60     10.128.0.7
nginx.companyci.com.  TXT   300    "heritage=external-dns,external-dns/owner=companyci-external-dns"

$TTL doesn't seem to be set on my SOA records by default.
I'll see if this is something that is usable.

Here's a related issue with the NodeJS CloudDNS SDK: googleapis/nodejs-dns#9

edit: Looks like you can update the SOA with a transaction in the CLI: googleapis/google-cloud-ruby#320

[benley]

Hi @njuettner, is this resolved via a new feature somewhere, or is the issue closed more like "wontfix"? I'm okay either way, just would like to know the outcome.