Tags for types of incidents

[danny-lloyd]

• Tags for services that the incident applies to
• Machine readable so that we could in future have
  • a JASMIN status page that just picks up relevant incidents
  • the MOTD only show some categories but not ones that don't apply like MOLES downtime
  • a CEDA services specific status page
• If each service has a tag then we could create a list on the status page of services that are up based on the fact that they aren't tagged in any current incident