lighthouse/book/src/local-testnets.md

Local Testnets

This section is about running your own private local testnets.

• If you wish to join the ongoing public testnet, please read become a validator.

It is possible to create local, short-lived Lighthouse testnets that don't require a deposit contract and Eth1 connection. There are two components required for this:

1. Creating a "testnet directory", containing the configuration of your new testnet.
2. Using the --dummy-eth1 flag on your beacon node to avoid needing an Eth1 node for block production.

There is a TL;DR (too long; didn't read), followed by detailed steps if the TL;DR isn't adequate.

TL;DR

lcli new-testnet
lcli interop-genesis 128
lighthouse bn --testnet-dir ~/.lighthouse/testnet --dummy-eth1 --http
lighthouse vc --testnet-dir ~/.lighthouse/testnet --allow-unsynced testnet insecure 0 128

Optionally update the genesis time to now:

lcli change-genesis-time ~/.lighthouse/testnet/genesis.ssz $(date +%s)

1. Creating a testnet directory

1.1 Install lcli

This guide requires lcli, the "Lighthouse CLI tool". It is a development tool used for starting testnets and debugging.

Install lcli from the root directory of this repository with:

cargo install --path lcli --force

1.2 Create a testnet directory

The default location for a testnet directory is ~/.lighthouse/testnet. We'll use this directory to keep the examples simple, however you can always specify a different directory using the --testnet-dir flag.

Once you have lcli installed, create a new testnet directory with:

lcli new-testnet

• This will create a "mainnet" spec testnet. To create a minimal spec use lcli --spec minim new-testnet.
• The lcli new-testnet command has many options, use lcli new-testnet --help to see them.

1.3 Create a genesis state

Your new testnet directory at ~/.lighthouse/testnet doesn't yet have a genesis state (genesis.ssz). Since there's no deposit contract in this testnet, there's no way for nodes to find genesis themselves.

Manually create an "interop" genesis state with 128 validators:

lcli interop-genesis 128

• A custom genesis time can be provided with -t.
• See lcli interop-genesis --help for more info.

2. Start the beacon nodes and validator clients

Now the testnet has been specified in ~/.lighthouse/testnet, it's time to start a beacon node and validator client.

2.1 Start a beacon node

Start a beacon node:

lighthouse bn --testnet-dir ~/.lighthouse/testnet --dummy-eth1 --http

• --testnet-dir instructs the beacon node to use the spec we generated earlier.
• --dummy-eth1 uses deterministic "junk data" for linking to the eth1 chain, avoiding the requirement for an eth1 node. The downside is that new validators cannot be on-boarded after genesis.
• --http starts the REST API so the validator client can produce blocks.

2.2 Start a validator client

Once the beacon node has started and begun trying to sync, start a validator client:

lighthouse vc --testnet-dir ~/.lighthouse/testnet --allow-unsynced testnet insecure 0 128

• --testnet-dir instructs the validator client to use the spec we generated earlier.
• --allow-unsynced stops the validator client checking to see if the beacon node is synced prior to producing blocks.
• testnet insecure 0 128 instructs the validator client to use insecure testnet private keys and that it should control validators from 0 to 127 (inclusive).