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| title | sort_key |
|---|---|
| Connecting to Consensus Clients | A3 |
Geth is an execution client. Historically, an execution client alone has been enough to run a full Ethereum node. However, Ethereum will soon swap its consensus mechanism from proof-of-work (PoW) to proof-of-stake (PoS) in a transition known as The Merge.
When that happens, Geth will not be able to track the Ethereum chain on its own. Instead, it will need to be coupled to another piece of software called a "consensus client". For Geth users that intend to continue to run full nodes after The Merge, it is sensible to start running a consensus client now, so that The Merge can happen smoothly. There are five consensus clients available, all of which connect to Geth in the same way.
This page will outline how Geth can be set up with a consensus client in advance of The Merge (or to interact with an alread-merged testnet).
{% include note.html content=" It is recommended to practise connecting a consensus client to Geth on a testnet such as Sepolia or Goerli but to wait until merge-ready releases are available before doing it on Ethereum Mainnet." %}
Configuring Geth
Geth can be downloaded and installed according to the instructions on the Installing Geth page. In order to connect to a consensus client, Geth must expose a port for the inter-client RPC connection.
The RPC connection must be authenticated using a jwtsecret file. This is created and saved
to <datadir>/geth/jwtsecret by default but can also be created and saved to a custom location or it can be
self-generated and provided to Geth by passing the file path to --authrpc.jwtsecret. The jwtsecret file
is required by both Geth and the consensus client.
The authorization must then be applied to a specific address/port. This is achievd by passing an address to
--authrpc.addr and a port number to --authrpc.port. It is also safe to provide either localhost or a wildcard
* to --authrpc.vhosts so that incoming requests from virtual hosts are accepted by Geth because it only
applies to the port authenticated using jwtsecret.
The Merge itself will be triggered using a terminal total difficulty (TTD). The specific value for the TTD has not yet been decided. When it is decided, Geth needs to know what it is in order to merge successfully. This will most likely be included in a new release, so Geth will have to be stopped, updated and restarted in advance of The Merge.
A complete command to start Geth so that it can connect to a consensus client looks as follows:
geth --authrpc.addr localhost --authrpc.port 8551 --authrpc.vhosts localhost --authrpc.jwtsecret /tmp/jwtsecret
Consensus clients
There are currently four consensus clients that can be run alongside Geth. These are:
Lighthouse: written in Rust
Nimbus: written in Nim
Prysm: written in Go
Teku: written in Java
It is recommended to consider client diversity when choosing a consensus client. Instructions for installing each client are provided in the documentation linked in the list above.
The consensus client must be started with the right port configuration to establish an RPC connection
to the local Geth instance. In the example above, localhost:8551 was authorized
for this purpose. The consensus clients all have a command similar to --http-webprovider that
takes the exposed Geth port as an argument.
The consensus client also needs the path to Geth's jwt-secret in order to authenticate the RPC connection between them.
Each consensus client has a command similar to --jwt-secret that takes the file path as an argument. This must
be consistent with the --authrpc.jwtsecret path provided to Geth.
The consensus clients all expose a Beacon API that can be used to check the status of the Beacon client or download blocks and consensus data by sending requests using tools such as Curl. More information on this can be found in the documentation for each consensus client.
Validators
After The Merge, miners are no longer responsible for securing the Ethereum blockchain. Instead, this becomes the responsibility of validators that have staked at least 32 ETH into a deposit contract and run validator software. Each of the consensus clients have their own validator software that is described in detail in their respective documentation. The easiest way to handle staking and validator key generation is to use the Ethereum Foundation Staking Launchpad. The launchpad is also available for Prater, Ropsten and Kiln testnets. It is also highly recommended to review the Merge readiness checklist.
Using Geth
After the merge, Geth will follow the head of the chain via its connection to the consensus client. However, Geth is still
the portal for users to send transactions to Ethereum. Overall, Geth will not change very much from a user-perspective.
The Geth Javascript console is still available for this purpose, and the majority of the JSON-RPC API will
remain available via web3js or HTTP requests with commands as json payloads. These options are explained in more detail on the
Javascript Console page. The Javascript console can be started using the following command
in a separate terminal (assuming Geth's IPC file is saved in datadir):
geth attach datadir/geth.ipc
Testnets
Ethereum Mainnet has not yet undergone The Merge, but some public testnets have. This means that running Geth alone is no longer enough to interact with merged testnets. This includes two testnets that were purpose built to test The Merge (Kiln, Kintsugi) and the long-standing public PoW chain, Ropsten, as well as the relatively new testnet Sepolia. If Geth is connected to these merged networks alone it will simply stall when it syncs as far as the merge block, awaiting information from a consensus client. Therefore, any activity on these testnets requires Geth to be connected to a consensus client. There are many instructional articles that exlain how to connect to these testnets using Geth in combination with various consensus clients, for example:
Connecting to Kiln using Lighthouse
Connecting to Kiln using Prysm
Connecting to Ropsten using Lighthouse
The Merge testing will soon progress to merging the Goerli testnet. Once this has happened Geth will require a connection to a consensus client to work on those networks too.
Summary
As The Merge approaches it is important for Geth users to prepare by installing and running a consensus client. Otherwise, Geth will stop following the head of the chain immediately after The Merge. There are five consensus clients to choose from. This page provided an overview of how to choose a consensus client and configure Geth to connect to it. This pre-emptive action will protect against disruption to users as a result of The Merge.