A few things we have noticed recently when it comes to Galera Manager support requests, that we feel we should address in this blog post.
First and foremost, it is a requirement that you install Galera Manager on a clean host. This means you install the base operating system and nothing else: no Nginx, no Apache, no InfluxDB, etc. The Galera Manager installer (gm-installer) will pull all the requisite packages, set SELinux to permissive during the install, etc. The next release of the gm-installer aims to be less fragile when it comes to this, and will aggressively handle installs on machines that already have software installed on it.
The other common issue is the inability to access ports, generally blocked by a firewall (gm-installer should have fixed this as long as setup is going properly), or some other reason. What gm-installer cannot fix is if your firewall is beyond Linux, i.e. some hardware based firewall blocking port access.
It goes without saying that you must run gm-installer as a superuser, i.e. root. You can achieve this by doing sudo su or just run it via sudo, i.e. sudo ./gm-installer.
You also do need to run gm-installer on a machine that has access to the Internet. It is not possible to run the installation offline, even if you have managed to grab the packages.