systemd service unit file for Greenlight (BigBlueButton Frontend)

greenlight.service

[Unit]
Description=Frontend for BigBlueButton conferencing system
After=network.target

[Install]
WantedBy=multi-user.target

[Service]
# Directory where greenlight is installed
WorkingDirectory=/opt/greenlight
# temp data / see below
CacheDirectory=greenlight
# Settings file from sample.env (https://github.com/bigbluebutton/greenlight/blob/master/sample.env)
EnvironmentFile=/etc/default/greenlight
Environment="RAILS_ENV=production"
Environment="PORT=8000"

# only writable Location: CacheDirectory - for temporary data (i.e. bundle startup)
Environment="HOME=/var/cache/greenlight"

Type=exec
ExecStartPre=bundle exec rake db:migrate
ExecStart=bundle exec puma -C config/puma.rb

TimeoutSec=15
Restart=always

# Prevent writes to /usr, /boot, and /etc
DynamicUser=yes
ProtectSystem=strict
NoNewPrivileges=true
ProtectHome=true

Maybe you want to set the After to postgresql.service.