Traffic Ops /api/1.4/cdns/name/{name}/dnsseckeys returns 500 if Snapshot or DS TTL Parameter doesn't exist

[rob05c]

The problem is, the 1.4 endpoint adds the DS Record text, which must come from the Snapshot, and which requires the DS TTL to construct.

There are a few ways we can fix this

1. Still require those things, and return a 400 with a helpful message if they don't exist, e.g. "CDN must be snapshotted", "a Parameter name 'tld.ttls.DS' config file 'CRConfig.json' must exist on the profile of a server on this CDN".
2. Automatically create an initial Snapshot when a CDN is created.
3. Automatically create a Parameter when a CDN's DNSSEC is turned on. This may not be possible, because the Parameter currently must be on a Server's Profile, and no servers may exist.
4. Use a default TTL if the Parameter/Snapshot doesn't exist. This should be the same default the Router uses, if the TTL doesn't exist in the CRConfig. I'm not sure this is an acceptable solution, if the Router has no default.
5. Move the mandatory tld.ttls.DS data to a table/row which must exist if DNSSEC is enabled. I know we aren't willing to do that work, but I feel obligated to note it's a solution, and the ideal solution which will make errors like this impossible.

My current intention is #4, and log a warning. It's not ideal, but it's relatively quick to implement, and mostly right.

I specifically do not think we should simply omit the DS Record from 1.4 if we can't create it. The new version is defined to return it, and it could break any number of things if it simply isn't there.

[rob05c]

@jhowell-comcast if you have any comments/suggestions.