Moving a Validating Node

This guide is for active validators who want to move their node to another machine. There are two primary methods to achieve this, outlined below.

Method One: Copying the Data to a New Location

This method is simple but requires downtime. The node needs to download all the blocks generated while it is stopped.

1. Stop the node.

2. Copy the node's data to a new mount:

   rsync -av --inplace --sparse  /var/lib/casper/ /new_mount

3. Change the mount point.

4. Restart the node.

Method Two: Swapping Keys with a Hot Backup

This method is a safer option, limiting downtime and enabling a smooth transition from the old to the new node. It keeps the node in sync with the tip of the chain.

1. Once a node is running (current_node), create a second node (backup_node) on another machine. These two nodes will run in parallel.
2. When the backup_node is up to date, stop both nodes.
3. Swap their associated keys.
4. Restart the backup_node.

Preparation for swapping

Let both nodes synchronize to the tip of the blockchain. Keep the current validating node running with the original validator keyset.

Bond the backup_node and wait until rewards are issued.

To swap keys:

1. Create the following folder structure on both nodes under the /etc/casper/validator_keys/ directory.
2. Create subdirectories for the current_node and backup_node.
3. Copy each node's keyset under the corresponding directories.

/etc/casper/validator_keys/
├── public_key.pem
├── public_key_hex
├── secret_key.pem
├── current_node
│   ├── public_key.pem
│   ├── public_key_hex
│   └── secret_key.pem
└── backup_node
|   ├── public_key.pem
|   ├── public_key_hex
|   └── secret_key.pem

This setup allows key swapping by running the sudo -u casper cp * ../ command, as shown below.

Swapping the nodes

On the current_node, run these commands:

sudo systemctl stop casper-node-launcher
cd /etc/casper/validator_keys/backup_node
sudo -u casper cp * ../

On the backup_node (the future validator), run these commands:

sudo systemctl stop casper-node-launcher
cd /etc/casper/validator_keys/current_node
sudo -u casper cp * ../
sudo systemctl start casper-node-launcher

Restart the original validator node (current_node), which is now the new backup:

sudo systemctl start casper-node-launcher

Understanding rewards impact

After swapping, the new validator node shows no round length until an era transition occurs and will lose all rewards from the point of the switch until the end of that era. The validator is not ejected but will receive rewards starting with the next era.

tip

You could time the swap right before the era ends to minimize reward losses.

Checking file permissions

After the swap, check and fix file permissions by running the /etc/casper/node_util.py utility.