Microsoft has revealed that Thursday’s outage was caused by a code defect that allowed the Azure DNS service to become overwhelmed and not respond to DNS queries. The outage was so wide-spread within Microsoft’s infrastructure that even their Azure status page, which is used to provide outage info, was inaccessible. Microsoft’s eventually resolved the outage at approximately 6:30 PM EST, with some services taking a bit longer to function again. Microsoft does not explain what this anomalous surge of DNS queries was, it may have been a DDoS attack targeting certain domains.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-outage-caused-by-overloaded-azure-dns-servers/