# Pre-Installation Preparation

## Assumptions
Omnia assumes that prior to installation:
* Systems have a base operating system (currently CentOS 7 or 8)
* Network(s) has been cabled and nodes can reach the internet
* SSH Keys for `root` have been installed on all nodes to allow for password-less SSH
* Ansible is installed on the master node
```
yum install ansible
```

## Example system designs
Omnia can configure systems which use Ethernet- or Infiniband-based fabric to connect the compute servers.

![Example system configuration with Ethernet fabric](images/example-system-ethernet.png)

![Example system configuration with Infiniband fabric](images/example-system-infiniband.png)

## Network Setup
Omnia assumes that servers are already connected to the network and have access to the internet.
### Network Topology
Possible network configurations include:
* A flat topology where all nodes are connected to a switch which includes an uplink to the internet. This requires multiple externally-facing IP addresses
* A hierarchical topology where compute nodes are connected to a common switch, but the master node contains a second network connection which is connected to the internet. All outbound/inbound traffic would be routed through the master node. This requires setting up firewall rules for IP masquerade, see [here](https://www.server-world.info/en/note?os=CentOS_7&p=firewalld&f=2) for an example.
### IP and Hostname Assignment
The recommended setup is to assign IP addresses to individual servers. This can be done manually by logging onto each node, or via DHCP. In addition, hostnames should be assigned