How To: Checkpoint Sync

This guide covers the additional steps required to checkpoint sync a beacon node from another beacon node that you trust.
This guide does not cover setting up an entire node from scratch.

:warning: You should always verify that your beacon node is synced correctly after doing a checkpoint sync.
Check Step 4 for instructions

More reading on checkpoint sync:

EF DevOps Endpoints

The EF DevOps team runs a handful of endpoints to help with syncing a testnet node.

Goerli/Prater: https://goerli.checkpoint-sync.ethpandaops.io
Sepolia: https://sepolia.checkpoint-sync.ethpandaops.io

Tutorial

Step 1

Note down the beacon endpoint you’re planning to checkpoint sync from. This can be another beacon node you run, a beacon node that a friend runs, one of the endpoints above, or any beacon node you trust.

Note: The source beacon node must be for the same Ethereum network as your beacon node.

For this tutorial we will use the EF DevOps Goerli endpoint (https://goerli.checkpoint-sync.ethpandaops.io)

Step 2

Add the checkpoint sync argument to your client. The flag is different between clients.

Prysm

--checkpoint-sync-url=https://goerli.checkpoint-sync.ethpandaops.io
--genesis-beacon-api-url=https://goerli.checkpoint-sync.ethpandaops.io

Lighthouse

--checkpoint-sync-url=https://goerli.checkpoint-sync.ethpandaops.io

Teku

--initial-state=https://goerli.checkpoint-sync.ethpandaops.io/eth/v2/debug/beacon/states/finalized

Lodestar

--checkpointSyncUrl=https://goerli.checkpoint-sync.ethpandaops.io

Nimbus

Requires the trustedNodeSync command to be run before the beacon is launched. Read more here: https://nimbus.guide/trusted-node-sync.html

Step 3

Start your client. Once started, check your logs for details surrounding the checkpoint process.

Note: You must be starting your client with a fresh data directory/database

Prysm

level=info msg="requesting https://goerli.checkpoint-sync.ethpandaops.io/eth/v2/debug/beacon/states/genesis"
level=info msg="requesting https://goerli.checkpoint-sync.ethpandaops.io/eth/v2/debug/beacon/states/finalized"

Lighthouse

INFO Starting checkpoint sync                remote_url: https://goerli.checkpoint-sync.ethpandaops.io, service: beacon
INFO Loaded checkpoint block and state       state_root: 0xb6e8c25393411f252775f82b4907298572003ac37acf9422dd2500b5c368a08d, block_root: 0xefe19ea0d99bf45d50d4302f6bbc3feb2c1ec46f8d6e112594ec86b9581596ae, slot: 3480832, service: beacon

Teku

INFO  - Loading initial state from https://goerli.checkpoint-sync.ethpandaops.io/eth/v2/debug/beacon/states/finalized
INFO  - Loaded initial state at epoch 11348 (state root = 0x08dab651bd667b166a0c99b7a21ee455f4f9fadfce0e37dbcee490f5ec841477, block root = 0xa5bd8b3eaadd81f892f120219f3bcee6565a37d045bf0cee4c4023a51def430c, block slot = 363136).  Please ensure that the supplied initial state corresponds to the latest finalized block as of the start of epoch 11348 (slot 363136).

Lodestar

info: Fetching weak subjectivity state weakSubjectivityServerUrl=https://goerli.checkpoint-sync.ethpandaops.io
info: Download completed

Nimbus

Starting trusted node sync                 databaseDir=/data/consensus/db restUrl=https://goerli.checkpoint-sync.ethpandaops.io blockId=finalized backfill=false reindex=false
Downloading checkpoint block               restUrl=https://goerli.checkpoint-sync.ethpandaops.io blockId=finalized
Downloading checkpoint state               restUrl=https://goerli.checkpoint-sync.ethpandaops.io checkpointSlot=370528
Writing checkpoint state
Writing checkpoint block
Database initialized, historical blocks will be backfilled when starting the node

Step 4

Validate that your node is on the expected chain. To do this we’ll check the state root of the finalized checkpoint against another source. For this guide we’ll use prater.beaconcha.in (the beaconcha.in instance for Goerli) but any source that you trust is fine.

You will need to know the IP & Port of your beacon node.

Default ports:

Lighthouse: 5052
Nimbus: 5052
Teku: 5051
Prysm: 3500
Lodestar: 9596

1. Obtaining finalized checkpoint & state root

Option A
  1. Open http://YOUR_NODE_IP:YOUR_NODE_PORT/eth/v1/beacon/headers/finalized in your browser.
  2. Find the slot number.
  3. Find the state_root value.
Option B
  1. Install curl and jq.
  2. In a new terminal window run:
curl -s http://YOUR_NODE_IP:YOUR_NODE_PORT/eth/v1/beacon/headers/finalized  | jq .'data.header.message'
  1. Find the slot and state_root values.

2. Validate against a known source

If it’s a match, congratulations :tada:. If it’s not a match you should start from scratch by wiping your beacon node and starting from the top.

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