How to launch EC2 instance with Boto, specifying size of EBS?

Question

I'm using boto/python to launch a new EC2 instance that boots from an EBS volume. At the time I launch the instance, I'd like to override the default size of the booting EBS volume.

I found no boto methods or parameters that might fit into my launch code:

ec2 = boto.connect_ec2( ACCESS_KEY, SECRET_KEY, region=region )

reservation = ec2.run_instances( image_id=AMI_ID, 
                                 key_name=EC2_KEY_HANDLE, 
                                 instance_type=INSTANCE_TYPE,
                                 security_groups = [ SECGROUP_HANDLE, ] )

This web page shows how to increase the size of a running EC2-instance's EBS volume using command-line tools, but I'd like to use boto at the time the EC2 instance is specified:

Answer 1

You have to create a block device mapping first:

dev_sda1 = boto.ec2.blockdevicemapping.EBSBlockDeviceType()
dev_sda1.size = 50 # size in Gigabytes
bdm = boto.ec2.blockdevicemapping.BlockDeviceMapping()
bdm['/dev/sda1'] = dev_sda1 

After this you can give the block device map in your run_instances call:

reservation = ec2.run_instances( image_id=AMI_ID, 
                                 key_name=EC2_KEY_HANDLE, 
                                 instance_type=INSTANCE_TYPE,
                                 security_groups = [ SECGROUP_HANDLE, ],
                                 block_device_mappings = [bdm])

Unfortunately this is not really well documented, but the example can be found in the source code.