I'm not sure I'm asking this question correctly, but what kind of performance hit do I take by using a Docker container within an EC2 instance instead of just running straight on the EC2 instance's userspace?
I'm not looking for any kind of concrete number, but let's say I've got a Postgres running on an m1.large. Any idea how running Postgres under Docker would change my performance characteristics?
That's correct, you can approximate the overhead of LXC (and any other similar containerization such as OpenVZ, Solaris Zones, BSD jails etc.) as zero. In terms of performance they are closer to chroot than to a virtual machine.
I'm not looking for any kind of concrete number, but let's say I've got a Postgres running on an m1.large. Any idea how running Postgres under Docker would change my performance characteristics?