The services appear to have been down for approximately 20 minutes at the time of posting and it is unclear how long the outage might last. At the current time, iMessage appears to be working fine.
Update 4:12 PM PT: As noted in our forums, it appears the outage is caused by a Google DNS issue. Apple services and web pages are accessible after turning off Google DNS.
Update 4:33 PM PT: The issue appears to have been resolved and all Apple services are now functioning as normal with Google DNS.