400 Bad Request
X-Instance-ID header is missing from request.

Metadata is available from VM and accessible through metadata proxy, which poplulates request with instance ID and gives metadata server clues which metadata return in answer. Metadat proxy, in general, is accessible on address 169.254.169.254 and pinned either to DHCP or VR entity of the VM's subnet depending on configuration (neutron/dhcp_agent.ini, neutron/l3_agent.ini), e.g.

VM$ netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
169.254.169.254 25.1.4.10       255.255.255.255 UGH       0 0          0 eth0

where in example 25.1.4.10 is DHCP server of eth0's subnet.

If you'll try to access metadata from inside of your VM, you will get what you're looking for:

VM$ curl http://169.254.169.254/2007-01-19/meta-data/
ami-id
ami-launch-index
ami-manifest-path
hostname
instance-id
local-hostname
local-ipv4
public-hostname
public-ipv4
reservation-id