Starting a long-running process in cloud-init on ec2 instance

I'm trying and failing to start a long-running command on launch of an EC2 (Amazon Linux). It needs to run under the ec2-user account. This was my first attempt:

#!/bin/bash
echo 'Woot 1!' > /home/ec2-user/woot1.txt
pushd /home/ec2-user/my-app-dir
nohup sudo -u ec2-user /home/ec2-user/my-app-dir/my_process.py &
echo 'Woot 2!' > /home/ec2-user/woot2.txt

The key command I'm trying to run is the "nohup" line, to run my_process.py.

The shell script works when I run it as root from a shell, but when I supply it in user-data to ec2-run-instances and login to the instance, I see both woot1.txt and woot2.txt, but my_process.py is not running. What's more, my_process.py creates a log file when it runs, but there is no log file there (and no nohup.out either) when I supply the script as user-data to ec2-run-instances.

I've tried putting the same things in a cloud-init form as well, with the same results:

#cloud-config
runcmd:
 - echo 'Woot 1!' > /home/ec2-user/woot1.txt
 - pushd /home/ec2-user/my-app-dir
 - nohup sudo -u ec2-user /home/ec2-user/my-app-dir/my_process.py &
 - echo 'Woot 2!' > /home/ec2-user/woot2.txt

If anyone can tell me where I'm going wrong, I'd appreciate it.