Executing multiple scripts on startup in a particular order

Question

I am running Raspbian GNU Linux (9) Stretch, on my Raspberry Pi 3.

Project Overview

1. Python script which makes use of 2 inputs to the Pi. Calculations are performed based on these inputs, and values are stored in a database.
2. A separate Django website which reads values from this database and updates the content of the web page.

Django Server run using: /home/pi/mysite/manage.py runserver 127.0.0.1:8000

Python Script located at: /home/pi/Desktop/myscript.py

On startup I would like to first make sure that my Django server is up and running and then start my python script.

What I have done so far

I came across the following question, but this is not what I am looking for. However most of the information is highly relevant.

if Type=simple in your unit file, you can only specify one ExecStart, but you can add as many ExecStartPre,ExecStartPost`, but none of this is suited for long running commands, because they are executed serially and everything one start is killed before starting the next one.

If Type=oneshot you can specify multiple ExecStart, they run serially not in parallel.

Initially I started by trying to get the python script to run on startup. To do this I am using a simple systemd service as follows.

[Unit]
Description=My script

[Service]
ExecStart=/usr/bin/python3 /home/pi/Desktop/myscript.py

[Install]
WantedBy=multi-user.target

This runs without error and initiates the python script on startup.

However, I cannot get my Django server up and running inside the same systemd service since only one ExecStart is allowed. I need both to be run in parallel.

Any suggestions on how this can be done?-

Answer 1

Solved

The simplest solution I found was to create another Unit:

[Unit]
Description=Mysite

[Service]
ExecStart=/usr/bin/python3 /home/pi/mysite/manage.py runserver 127.0.0.1:8000

[Install]
WantedBy=multi-user.target

We can enable it using:

rpi ~$ sudo systemctl enable mysite.service

Next we need to edit the myscript.service, such that this runs before mysite.service.

[Unit]
Description=My script

[Service]
ExecStart=/usr/bin/python3 /home/pi/Desktop/myscript.py
Wants=mysite.service 

[Install]
WantedBy=multi-user.target

The difference between Wants and Requires can be found here.