Setup: Local Cluster with Polar

Install Polar

This tutorial will leverage the Polar application for setting up a local cluster of Lightning Network nodes on regtest. Polar can be downloaded for MacOS, Linux, and Windows. The source code is hosted on Github.

Polar website

Mac and Windows users will need to install Docker Desktop as a dependency before using Polar. Linux users will need to download both Docker Server and Docker Compose.

Core UI Components

After downloading, installing, and running Polar, the following welcome screen will appear.

Polar welcome screen

There are three options for users in the top right:

  1. Create Network: spin up a new cluster of LND, c-lightning, eclair, and bitcoind nodes. This will create a Docker container within which Polar will operate.

  2. Import Network: download a pre-built cluster of Lightning nodes for local testing.

  3. Manage Images: customize the command used to start various versions of LND, c-lightning, eclair, and bitcoind nodes.

This tutorial will first focus on Create Network, so click either the orange “Create a Lightning Network” button in the middle, or Create Network in the top right corner.

Create and Start a Network

Create Network Screen

After clicking Create Network, the following screen should appear. As previously mentioned, it allows you to specify how many of each node implementations your cluster will be composed of.

Note: You will always need at least one Bitcoin Core node!

Create a new Lightning Network with the following parameters:

  • Network Name = test01

  • How many Managed Nodes?

    • LND = 2

    • c-lightning = 0

    • Eclair = 0

    • Bitcoin Core = 1

After clicking the orange Create Network button, Polar should display this new interface.

New Network Screen, Pre-Boot

Press the orange Start button in the top right corner to start your local network. It takes a couple seconds for the nodes to boot up, but the indicator lights will eventually turn green signaling that the process has completed. Once this has happened, click on “alice” the lnd node to see the below screen.

New Network Screen, Post-Boot

Most of the information on this screen is self-explanatory. The local regtest instance is only at Block Height = 1 so alice’s Confirmed Balance and Unconfirmed Balance are both 0 sats. To change that, click on the Actions tab for alice, ensure Deposit Funds is set to 1,000,000 and press Deposit.

Alice's Action Tab

Two numbers should have changed after clicking Deposit. First, the height number in the top status bar incremented from 1 to 107. That is because it takes 100 blocks for a coinbase reward to become spendable by a bitcoind node (if you click on backend1, you’ll see a Spendable Balance of >349 BTC and an Immature Balance of >5000 BTC), and an additional 6 blocks for a deposit to lnd to be confirmed. Second, alice’s balance in the top right of her node panel increased from 0 to 1.0M sats, signifying the successful deposit.

Create and Pay an Invoice

Now that alice’s on-chain wallet has been funded, it’s time to open a channel. Click Open Channel -> Outgoing, select bob as the Destination, accept the default Capacity (sats) of 250,000, and click the orange Open Channel button.

Once the channel has been opened, click on the new green line between alice and bob’s lnd nodes to see the below screen.

New Channel Details

Hovering over the green dot on alice’s node will display “Source”, while hovering over the blue dot on bob’s node will display “Destination”. This is to signify which side of the channel has the Source Balance of 240,950 sats, and which side has the Destination Balance of 0 sats.

Since bob has no Destination Balance, right click on his node open an Actions panel, and select Create Invoice. Accept the default 50,000 sat Amount, and press the orange Create Invoice button. Successfully doing so should create this screen.

Invoice Success

Click on Copy & Close, right click on alice’s node, and select Pay Invoice. Paste the invoice you copied from the above screen into the Bolt 11 Invoice field, and click the orange Pay Invoice button. After doing so, the alice, bob, and channel dashboards should look like this:

Alice, Bob, and Channel Success

Congratulations! You’ve made your first successful Lightning Network payment on regtest!

Before moving on, click on bob’s lnd node and over to his Connect dashboard. The url:port information for bob’s GRPC Host, REST Host, P2P Internal, and P2P External will be useful in the next section, as will the Hex details of bob’s TLS Cert and Admin Macaroon.

Bob Connect

Now, click the red Stop button in the top right corner and prepare for the next section.