One of the happy netlab users sent me an interesting challenge:

• He’s built a large lab and added tons of extra configuration to the lab devices.
• Afterwards, he realized he’d like to add a few more devices to the lab and was worried about losing all the changes he had made.

Unfortunately, you cannot add new devices to an already-running lab. You must shut down the lab, change the topology description, and start a new lab. However, there are things you can do to preserve the extra work you already did:

• Save the current device configurations with netlab collect -o folder. Make sure you specify an output folder; by default, netlab saves the configurations in the config folder, which the netlab down --cleanup command removes..
• Check whether you can load the saved configurations with netlab config your_folder --check (the --check option is passed to Ansible)
• Shut down the lab, change the topology file, and restart the lab.
• Add the saved configurations to the lab devices with netlab config your_folder. The command will fail for all devices you added to the lab, but should merge the saved configurations with those generated from the modified lab topology.

The above procedure definitely works on most Cisco platforms (IOS/XE, NX-OS, IOS-XR) and Arista EOS, Aruba AOS, and Dell OS10; it most probably works on Juniper platforms. Here’s what the actual limitations are:

• You have to get the whole device configuration with netlab collect
• netlab collect must save the device configuration in a single text file
• netlab config must be able to take that text file and push it as a new configuration to the device.

I never tested VyOS or Mikrotik, but I know you’ll experience problems in these scenarios:

• You cannot save the Linux or Fortinet configurations (details).
• You cannot save the data-plane configuration for FRR.
• You can reload only the FRRouting configuration onto FRR, Cumulus Linux 4.x, and SoNIC devices.
• Due to the way netlab configures Nokia SR Linux and Nokia SR-OS, you cannot use the saved device configuration with the netlab config command.

Finally, you could use netlab config --reload to reload the saved configurations to Nokia devices, but then you’d lose all the changes netlab made to configure the links and routing protocol parameters between the already-existing and the new devices. You could, however, run another netlab initial command (hopefully limited to Nokia devices; see below) after reloading the saved configurations.

$ netlab config saved --limit eos,iosv,iol
$ netlab config --reload saved --limit srlinux
$ netlab initial --limit srlinux

Fortunately, the networking engineer who wanted to expand his lab used Arista EOS devices, and the migration worked flawlessly.