From London, Slack was resolving to a load balancer in eu-west-2 earlier during the outage. It now resolves to eu-west-1 and I have no issues connecting to Slack.

  $ nslookup edgeapi.slack.com
  Server:  1.1.1.1
  Address: 1.1.1.1#53
  
  Non-authoritative answer:
  edgeapi.slack.com canonical name = prod-haproxy-edge-nlb-eip-038c466f971aa8b8.elb.eu-west-2.amazonaws.com.
  Name: prod-haproxy-edge-nlb-eip-038c466f971aa8b8.elb.eu-west-2.amazonaws.com
  Address: 35.176.156.206

  $ nslookup edgeapi.slack.com
  Server:  1.1.1.1
  Address: 1.1.1.1#53
  
  Non-authoritative answer:
  edgeapi.slack.com canonical name = prod-haproxy-edge-nlb-eip-1bffe8d4fbdf4b94.elb.eu-west-1.amazonaws.com.
  Name: prod-haproxy-edge-nlb-eip-1bffe8d4fbdf4b94.elb.eu-west-1.amazonaws.com
  Address: 18.200.77.145