- You can do this, but it's highly discouraged since it means no VPC peering if you ever need that.
- Can't do this at all with network interfaces, it all is via VPC peering.
- Can't change the VPC after an instance has been created, you have to take a snapshot and relaunch it.
I thought one would have a node two VPC, e.g. app and database, so it can speak to both, but the load balancers can't.
With peering one would have an app VPC and a database VPC and peer them?
Not sure best practice for DO since I haven't tried their VPC setup but it doesn't appear to have a way to let two VPCs interact yet.
- You can do it, but it's probably not a great idea if you need to do VPC peering (or attach multiple VPCs to one VM, see next).
- Does actually work, but it does not work if the VPCs you're trying to attach to a single VM have overlapping CIDRs.
- Same deal, almost. You cannot add or remove network interfaces from an existing VM.
If you're launching ephemeral networks for testing VMs / virtual appliances in their own, isolated networks, it can be totally feasible to have lots of them using the same addresses. You can only create 5 VPCs (at all) by default per AWS account, but they'll raise that limit for you if you request it.