From the AWS Service Health Dashboard this morning:

7:45 AM PDT We are investigating possible connectivity issues for a small number of instances in a single Availability Zone in the US-EAST-1 Region.

8:11 AM PDT We can confirm network connectivity issues for some EC2 instances in the US-EAST-1 region. Customers may be experiencing network impairment or connectivity issues to their EBS volumes performing read/write operations. We are actively working to resolve this issue.

8:37 AM PDT We can confirm network connectivity issues for some EC2 instances in a single Availability Zone in the US-EAST-1 region. Customers may be experiencing impaired read/write access to their EBS volumes. New instance launches are also delayed. We are actively working to resolve this issue.