Since Cloud Server v. 7.2, it's possible to upgrade gradually a Cloud Server environment from version 6 to v.7: upgrade before the nodes at your convenience and finally the Cloud Server.

Nodes v. 7 can work with a Cloud Server v. 6.
Nodes v. 6 cannot instead work with a Cloud Server v. 7 and are marked as 'invalid version'.

This is the suggested procedure.

Premises
i) Updating the NoMachine installation requires the termination of all the running sessions on that host. These sessions cannot be recovered later. This is necessary for installing the new libraries and binaries. Processes already loaded in the system memory lock down the corresponding binaries and libraries that cannot be otherwise replaced.
ii) The procedure implies a shutdown of all services. They are automatically restarted once the update procedure is completed.
iii) The procedure considers two cases: one single Cloud Server or two Cloud Servers in a HA failover cluster.

Step 1- Stop the node(s) you're going to update (optional)
As a precaution, we suggest to stop the node before proceeding with its upgrade.
This will prevent new connections to the node(s) but will not terminate sessions there. You can stop access to the node(s) from the Cloud Server host as explained below.

On Linux and macOS, execute the command as 'sudo' user or as 'root' and without 'sudo':
sudo /etc/NX/nxserver --serverstop <server:port>

On Windows, open a CMD console as administrator and execute:
cd C:\Program files (x86)\NoMachine\bin\
nxserver --serverstop <server:port>

Step 2- Then, proceed to update the node.
You can do that by installing a new package or via UI by means of the automatic updates from the NoMachine repositories. 

Step 3- Finally, re-enable accepting connections on the nodes by running the following commands on the Cloud Server host. Skip this point if you didn't stopped the nodes at point 1.

On Linux and macOS:
sudo /etc/NX/nxserver --serverstart <server:port>

On Windows, open a CMD console as administrator and execute:
cd C:\Program files (x86)\NoMachine\bin\
nxserver --serverstart <server:port>

TIP     
The 'nxserver --serverstop' and 'nxserver --serverstart' commands accept a comma-separated list of servers in the format of: <server1:port>,<server2:port>...
where <server1:port> is the name of the node as it appears in the output of 'nxserver --serverlist'.

Step 4- Once all nodes have been updated, update the Cloud Server.
Let's distinguish two cases, a single Cloud Server (Case I) or two Cloud Servers in a failover cluster (Case II).

Case I - Updating a single Cloud Server

Stop accepting connections on the Cloud Server by executing the following commands.

On Linux and macOS:
sudo /etc/NX/nxserver --stop

On Windows, open a CMD console as administrator and execute:
cd C:\Program files (x86)\NoMachine\bin\
nxserver --stop

Update the Cloud Server. The update procedure will restart automatically all the necessary services.

Case II - Updating the Cloud Server failover cluster

Step 1- Shutdown the Cloud Server on the secondary server host to avoid to activate the failover procedure when stopping Cloud Server on the primary server host.
To do that, execute the following command on the secondary server host.

On Linux and macOS:
sudo /etc/NX/nxserver --shutdown

On Windows, open a CMD console as administrator and execute:
cd C:\Program files (x86)\NoMachine\bin\
nxserver --shutdown

Step 2- Then stop accepting connections on the active Cloud Server by executing the following commands.

On Linux and macOS:
sudo /etc/NX/nxserver --stop

On Windows, open a CMD console as administrator and execute:
cd C:\Program files (x86)\NoMachine\bin\
nxserver --stop

Step 3- Now update the primary Cloud Server and the secondary Cloud Server. Order of update is not relevant.

Step 4- Finally restart both Cloud Servers after the update to make sure that the cluster interface is created on the primary server. Execute firstly on the primary CS host then on the secondary CS host the following command.

On Linux and macOS:
sudo /etc/NX/nxserver --restart

On Windows, open a CMD console as administrator and execute:
cd C:\Program files (x86)\NoMachine\bin\
nxserver --restart