Slack has provided detailed about what happened on Jan 4, the first workday of 2021, when it went down. ” We observed signs that we were seeing widespread network degradation, which we escalated to AWS, our main cloud provider,” Slack Said in a detailed statement. ” The mini-peak at 7 am PST — combined with the underlying network problems — led to saturation of our web tier.”  Which resulted in Slack becoming unavailable.