OpenStack compute service : error when trying to access the instances section

In the Horizon dashboard, I tried to access the instances section, which is part of the compute service. I got this error :

JSONDecodeError at /project/instances/
Expecting value: line 1 column 1 (char 0)
Request Method: 	GET
Request URL: 	http://localhost/dashboard/project/instances/
Django Version: 	3.2.10
Exception Type: 	JSONDecodeError
Exception Value: 	
Expecting value: line 1 column 1 (char 0)
Exception Location: 	/usr/lib/python3.8/json/, line 355, in raw_decode

I checked all the running devstack services, they were all running but one :

I tried to start this service only but it was not enough. I had to restart all services :

sudo systemctl restart devstack@*

Installing OpenStack on Ubuntu

Here are the steps to install OpenStack with DevStack on Ubuntu 20.04.3 LTS.
DevStack really simplifies the installation of OpenStack.
I followed the steps described here :
1) First you need to create the user “stack” :
sudo useradd -s /bin/bash -d /opt/stack -m stack
2) That user should have no password and have sudo privileges :
echo “stack ALL=(ALL) NOPASSWD: ALL” | sudo tee /etc/sudoers.d/stack
3) Login as the user stack :
sudo -u stack -i
4) Then clone the DevStack files :
git clone
5) Go to the devstack folder and create a file called local.conf :
cd devstack
/opt/stack/devstack/touch local.conf
Add the following content :

And finally launch the script that will install OpenStack :

2021-12-15 20:03:55.748 | completed in 1444 seconds. (it took a bit more than 20mn)

You can then login to the Horizon dashboard. Just go to the URL http://localhost. User/password : admin/secret

You can check the version installed :

And also launch OpenStack CLI :