geth readme

Flashbots Block Builder

This project implements the Flashbots block builder, based on go-ethereum (geth).

See also: https://docs.flashbots.net/flashbots-mev-boost/block-builders

Run on your favorite network, including Mainnet, Goerli, Sepolia and local devnet. Instructions for running a pos local devnet can be found here.

You will need to run a modified beacon node that sends a custom rpc call to trigger block building. You can use the modified prysm fork for this.

Test with mev-boost and mev-boost test cli.

Building geth requires both a Go (version 1.19 or later) and a C compiler. You can install them using your favourite package manager. Once the dependencies are installed, run

How it works

• Builder polls relay for the proposer registrations for the next epoch when block building is triggered
• If both local relay and remote relay are enabled, local relay will overwrite remote relay data. This is only meant for the testnets!

Limitations

• Does not accept external blocks
• Does not have payload cache, only the latest block is available

Usage

Configure geth for your network, it will become the block builder.

Builder-related options:

$ geth --help

   BUILDER

    --builder                      (default: false)
          Enable the builder

    --builder.beacon_endpoint value (default: "http://127.0.0.1:5052")
          Beacon endpoint to connect to for beacon chain data [$BUILDER_BEACON_ENDPOINT]

    --builder.bellatrix_fork_version value (default: "0x02000000")
          Bellatrix fork version. [$BUILDER_BELLATRIX_FORK_VERSION]

    --builder.dry-run              (default: false)
          Builder only validates blocks without submission to the relay

    --builder.genesis_fork_version value (default: "0x00000000")
          Gensis fork version. [$BUILDER_GENESIS_FORK_VERSION]

    --builder.genesis_validators_root value (default: "0x0000000000000000000000000000000000000000000000000000000000000000")
          Genesis validators root of the network. [$BUILDER_GENESIS_VALIDATORS_ROOT]

    --builder.listen_addr value    (default: ":28545")
          Listening address for builder endpoint [$BUILDER_LISTEN_ADDR]

    --builder.local_relay          (default: false)
          Enable the local relay

    --builder.no_bundle_fetcher    (default: false)
          Disable the bundle fetcher

    --builder.relay_secret_key value (default: "0x2fc12ae741f29701f8e30f5de6350766c020cb80768a0ff01e6838ffd2431e11")
          Builder local relay API key used for signing headers [$BUILDER_RELAY_SECRET_KEY]

    --builder.remote_relay_endpoint value
          Relay endpoint to connect to for validator registration data, if not provided
          will expose validator registration locally [$BUILDER_REMOTE_RELAY_ENDPOINT]

    --builder.secondary_remote_relay_endpoints value
          Comma separated relay endpoints to connect to for validator registration data
          missing from the primary remote relay, and to push blocks for registrations
          missing from or matching the primary [$BUILDER_SECONDARY_REMOTE_RELAY_ENDPOINTS]

    --builder.secret_key value     (default: "0x2fc12ae741f29701f8e30f5de6350766c020cb80768a0ff01e6838ffd2431e11")
          Builder key used for signing blocks [$BUILDER_SECRET_KEY]

    --builder.validation_blacklist value (default: "")
          Path to file containing blacklisted addresses, json-encoded list of strings.

    --builder.validator_checks     (default: false)
          Enable the validator checks

    MINER

    --miner.algotype value         (default: "mev-geth")
          Block building algorithm to use [=mev-geth] (mev-geth, greedy)

    --miner.blocklist value
          flashbots - Path to JSON file with list of blocked addresses. Miner will ignore
          txs that touch mentioned addresses.

    --miner.extradata value
          Block extra data set by the miner (default = client version)

   METRICS

   --metrics.builder value          (default: false)
            Enable builder metrics collection and reporting

Environment variables:

BUILDER_TX_SIGNING_KEY - private key of the builder used to sign payment transaction, must be the same as the coinbase address

Metrics

To enable metrics on the builder you will need to enable metrics with the flags --metrics --metrics.addr 127.0.0.1 --metrics.builder which will run a metrics server serving at 127.0.0.1:6060/debug/metrics. This will record performance metrics such as block profit and block building times. The full list of metrics can be found in miner/metrics.go.

See the metrics docs for geth for more documentation.

Blacklisting addresses

If you want to reject transactions interacting with certain addresses, save the addresses in json file with an array of strings. Deciding whether to use such a list, as well as maintaining it, is your own responsibility.

• for block building, use --miner.blocklist
• for validation, use --builder.validation_blacklist

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Details of the implementation

There are two parts of the builder.

1. ./builder responsible for communicating with the relay
2. ./miner responsible for producing blocks

builder module

Main logic of the builder is in the builder.go file.

Builder is driven by the modified consensus client that calls OnPayloadAttribute indicating that block should be produced. After requesting additional validator data from the relay builder starts building job with runBuildingJob. Building job continuously makes a request to the miner with the correct parameters and submits produced block.

• Builder retries build block requests every second on average.
• If the job is running but a new one is submitted for a different slot we cancel previous job.
• All jobs have 12s deadline.
• If new request is submitted for the same slot as before but with different parameters, we run these jobs in parallel. It is possible to receive multiple requests from CL for the same slot but for different parent blocks if there is a possibility of a missed block.
• All submissions to the relay are rate limited at 2 req/s
• Only blocks that have more profit than the previous best submissions for the particular job are submitted.

Additional features of the builder:

• Builder can submit data about build blocks to the database. It stores block data, included bundles, and all considered bundles. Implemented in flashbotsextra.IDatabaseService.
• It's possible to run local relay in the same process
• It can validate blocks instead of submitting them to the relay. (see --builder.dry-run)

miner module

Miner is responsible for block creation. Request from the builder is routed to the worker.go where generateWork does the job of creating a block.

• Coinbase of the block is set to the address of the block proposer, fee recipient of the validator receives its eth in the last tx in the block.
• We reserve gas for the proposer payment using proposerTxPrepare and commit proposer payment after txs are added with proposerTxCommit. We do it in a way so all fees received by the block builder are sent to the fee recipient.
• Transaction insertion is done in fillTransactionsAlgoWorker \ fillTransactions. Depending on the algorithm selected. Algo worker (greedy) inserts bundles whenever they belong in the block by effective gas price but default method inserts bundles on top of the block. (see --miner.algo)
• Worker is also responsible for simulating bundles. Bundles are simulated in parallel and results are cached for the particular parent block.
• algo_greedy.go implements logic of the block building. Bundles and transactions are sorted in the order of effective gas price then we try to insert everything into to block until gas limit is reached. Failing bundles are reverted during the insertion but txs are not.
• Builder can filter transactions touching a particular set of addresses. If a bundle or transaction touches one of the addresses it is skipped. (see --miner.blocklist flag)

Bundle Movement

There are two ways bundles are moved to builders

1. via API -sendBundle
2. via Database - flashbotsextra.IDatabaseService

fetcher service

• Fetcher service is part of flashbotsextra.IDatabaseService which is responsible for fetching the bundles from db and pushing into mev bundles queue which will be processed by builder.
• Fetcher is a background process which fetches high priority and low priority bundles from db.
• Fetcher fetches 500 high priority bundles on every head change, and 100 low priority bundles in the interval of every 2 seconds.

Block builder diagram

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Security

If you find a security vulnerability in this project or any other initiative related to proposer/builder separation in Ethereum, please let us know sending an email to security@flashbots.net.

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License

The code in this project is free software under the LGPL License.