Adding/Removing a Compute Node

This page describes the steps to add or remove a compute node from an existing SCEPTRE cluster.

Assumptions:

A SCEPTRE cluster has already been installed.

For adding: Compute node has the necessary connections and system packages

For removing: Compute node is still connected to the minimega mesh or is accessible via SSH.

Adding a compute node

Verify the compute node is successfully connected to the CTL and TDN networks.
Verify the necessary packages are installed on the compute node.
Verify the user on the compute node has sudo privileges WITHOUT using a password (See NOTE below).
From the headnode, connect the new compute node to the minimega mesh (in the command below, replace NEW_COMPUTE with the hostname of the new compute node and replace USERNAME with the username of the new compute node):
```
sudo minimega -e deploy launch NEW_COMPUTE USERNAME sudo
```
Verify the new compute node is connected to minimega mesh:
```
sudo minimega -e mesh list
```

NOTE: To allow USERNAME to use sudo without a password (replace USERNAME with the username of the new compute node), first open the sudoers file using: sudo visudo. Next add the following entry for USERNAME to the bottom of the file: USERNAME ALL=(ALL) NOPASSWD:ALL. Finally, save and close the file.

Removing a compute node

Verify there are no VMs running on the node.
From the headnode, remove the compute node from the minimega mesh (in the command below, replace COMPUTE with the hostname of the compute node to be removed):
```
sudo minimega -e mesh send COMPUTE quit
```