SRV polling (introduced in https://github.com/mongodb/specifications/blob/master/source/polling-srv-records-for-mongos-discovery/polling-srv-records-for-mongos-discovery.rst) adds a new server-discovery mechanism which is subject to the same success/failure modes as existing server discovery mechanisms. However, the SRV polling spec does not specify any events that are to be published when polling the DNS records results in success/failure. This could make it difficult to diagnose issues that stem from this new feature, as it would be hard to obtain runtime information about DNS polling.

We should update the spec to require drivers to publish at least the following events (names are suggestions):

• SRVLookupFailedEvent - published when SRV records cannot be retrieved due to a DNS failure.
• SRVRecordsEmptyEvent - published when the DNS lookup results in an empty seedlist.
• SRVRecordsChangedEvent - published when the DNS lookup results in a new seedlist.