In my experience, Coinbase/GDAX becomes unavailable every time the cost of Bitcoin drops significantly in a really short period of time... it happened again this morning a little before 7am... Not sure if they are trying to control the drops or if their servers can't handle the load.
I was wondering the same thing about GDAX/Coinbase. I've been seeing "partial" outages both on their portal and their API side. Partial outages are the worst, as they only leave 'some' of the participants unable to act.
