So although it's the same domain, slack.com, the records still resolve which seems to rule out a DNS related issue. DNS is served by AWS Route53 in all cases and only by Route53 (which might or might not be a great idea considering what happened to Dyn late last year).
Slack.com and the API are hosted by EC2, status.slack.com points to Rackspace.
I wonder what happened to take both down.
