Toolkit: DNS lookup can fail

[rix0rrr]

Reported by @ygoodmn:

CDK 0.9.2 on Ubuntu VM : running cdk deploy get disconnections, is there some retry. Seen this a few times

(node:19925) UnhandledPromiseRejectionWarning: Error: getaddrinfo EAI_AGAIN cloudformation.us-west-1.amazonaws.com:443
at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:67:26)
(node:19925) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:19925) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
❌ Deployment of stack cdk-sms104-WAF failed: NetworkingError: getaddrinfo EAI_AGAIN cloudformation.us-west-1.amazonaws.com:443
getaddrinfo EAI_AGAIN cloudformation.us-west-1.amazonaws.com:443

Happens DURING stack monitoring.

• Why is DNS lookup constantly happening? Don't we reuse the CFN client?

As per this thread:

EAI_AGAIN means the DNS server replied that it cannot currently fulfill the request. (If you want the hairy details, the RCODE field in the response is set to 2, SERVFAIL.)

[rix0rrr]

This will be a hard one to debug. We are instantiating some new CloudFormation clients, but the monitor in particular reuses the same client used to start the update, so that can't be it.