Python script from systemctl at launch

Question

I have 3 systemd services I created that run a Python script and pass a key argument because the scripts download datasets that require that key. When I enable the service it works just fine, but if I reboot the EC2 instance its on it fails on launch with:

(code=exited, status=255)

I want it to run on launch because I have a workflow that uses EventBridge to trigger a Lambda function that turns on the instance at specific time to download the dataset to S3 and begin the ETL process. Why would the service run as intended with $sudo systemctl start service-name.service but fails on startup?

Answer 1

Hmmm, this will depend on how you're running the EC2. Basically, there are two ways.

Via Cloud-init / EC2 userdata

You can specify if the script will be executed on the first boot (when the EC2 is created), every (re)boot, etc.

You can check the officials' docs for that:

Cloud-init: Event and Updates

AWS - Run commands on your Linux instance at launch

How can I utilize user data to automatically run a script with every restart of my Amazon EC2 Linux instance?

Via Linux systemd

You can use the example below (just remove the comments and/or just/add the Requires and After if it's needed.)

## doc here: https://man7.org/linux/man-pages/man5/systemd.unit.5.html#[UNIT]_SECTION_OPTIONS
[Unit]
Description=Startup script
# Requires=my-other-service.target
# After=After=network.target my-other-service.target

## doc here: https://man7.org/linux/man-pages/man5/systemd.service.5.html#OPTIONS
[Service]
Type=oneshot
ExecStart=/opt/myscripts/startup.sh

## doc here: https://man7.org/linux/man-pages/man5/systemd.unit.5.html#[INSTALL]_SECTION_OPTIONS
[Install]
WantedBy=multi-user.target