An important note if you want to use this right away:
This feature is currently available for the C3, C4, M3, R3, and T2 instance types running in the US East (Northern Virginia) region; we plan to make it available in other regions as quickly as possible. The instances must be running within a VPC, must use EBS-backed storage, but cannot be Dedicated Instances.
VPC-only sounds like a giant caveat, and it is, but this is a good opportunity to note that this is the trend now with AWS and the direction they're heading - (non-VPC) "EC2 Classic" is being gradually phased out, VPC is now the default for new accounts, and most new features are being added only to VPC. So, time for everyone to start thinking about migrating.
AWS recently announced ClassicLink [1], which helps with migration: "In order to allow EC2-Classic instances to communicate with these resources, we are introducing a new feature known as ClassicLink. You can now enable this feature for any or all of your VPCs and then put your existing Classic instances in to VPC security groups."
They will hopefully introduce a new "classic" (as an abstraction over VPC) at some point, unless they want to lose many low-end customers to "easier" clouds.
Having this level of control can be nice, but most of it really needs to be optional because for most deployments it does nothing other than add an excessive amount of unneeded complexity.
Some of the APIs are outright hostile, e.g. 'delete_vpc' which makes you track down half a dozen dependencies (without providing hints about which those might be) before you're allowed to delete a VPC.
> unless they want to lose many low-end customers to "easier" clouds.
I've never gotten the impression that AWS is interested in building a 'cloud' for those less technically inclined. Heroku and others fill that void, EC2 is where you move after Heroku doesn't fit the bill and before dedicated hardware does.
For people not yet on one of the newer instance types (HVM VPC), it is possible to migrate directly assuming you can tolerate a few minutes of downtime to make the final switch. This was the guide that helped me: https://forums.aws.amazon.com/thread.jspa?threadID=155526
This feature is currently available for the C3, C4, M3, R3, and T2 instance types running in the US East (Northern Virginia) region; we plan to make it available in other regions as quickly as possible. The instances must be running within a VPC, must use EBS-backed storage, but cannot be Dedicated Instances.