Upgrade Graylog server from el7 to el8

• Install a new server with EL8, using our kickstart file
• On the old server, stop graylog and backup its mongo database

systemctl stop graylog-server
pre-backup
# Copy /home/lbkp/mongo/graylog somewhere

• Shutdown the old server and start the new one with the same IP
• Ensure log listeners won't be accessible yet (either disable rules on the main firewall, or set graylog_http_src_ip to an empty array)
• Run the ansible playbook :

ansible-playbook -i inventories/fws.ini fws.yml -l graylog.fws.fr

• Stop Graylog service, copy the mongo dump on the new server, and restore graylog's mongo database

systemctl stop graylog-server
mongo graylog --eval "db.dropDatabase()"
mongorestore -d graylog /home/lbkp/mongo/graylog/
systemctl start graylog-server