Github's DNS likely will serve up a different IP for github when there is an outage. I can't talk about the details but GitHub and the rest of Microsoft use a global load balancing system that works through DNS.
Would be interesting to know what these fail over patterns are. As DNS takes a while to propagate, I thought DNS records already indicate fail over addresses.
I think only MX records indicate any priority for each additional record returned, for A records theres no indication of which records have priority over others and the usual behavior of authoritative DNS servers is to rotate the order in which records for the same thing are returned, so effectively returning more than one record for the same question results in a distribution of requests to the IPs returned rather than any sort of failover behavior.
In the case of the software Microsoft uses, it monitors endpoints for the websites in question and then changes which IP(s) are returned based on the availability of those endpoints, the geographic region and other factors.
