84 lines
3.2 KiB
Markdown
84 lines
3.2 KiB
Markdown
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---
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title: The Merge
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sort_key: A2
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---
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As an Execution-Layer (EL) client, Geth supports the transition of Ethereum from PoW to
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PoS, a.k.a. [The Merge](https://ethereum.org/en/upgrades/merge/). As this milestone
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approaches for the Ropsten testnet, users running a Geth node will need to keep a few
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things in mind to ensure a smooth transition.
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### Transition
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The transition will happen when a pre-announced total difficulty is reached by the chain.
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This is unlike usual forks which occur at a certain scheduled block number.
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The total difficulty threshold that triggers the Merge is also known as the *Terminal
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Total Difficulty* (TTD).
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{% include note.html content="In case of an emergency delay, the TTD can be overriden using `--override.totalterminaldifficulty`." %}
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### Consensus client
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After the Merge, Ethereum's Proof-Of-Stake consensus logic is handled by a separate piece
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of software called a Consensus-Layer (CL) client.
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This means running Geth alone will not suffice to be able to follow the chain. You must
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set up a consensus client and configure it so it can talk to Geth. This has to be done
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before the Merge event happens.
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The two clients will coordinate the transition together.
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You can choose one of several [Consensus Client implementations][cl-list].
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Note that CL clients are equipped with two modes. One for following the beacon chain
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(beacon node), and another mode used for validators. **It is NOT required to run a
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validator or stake 32 ETH in order to follow the chain!**
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### EL - CL communication
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ELs and CLs communicate using a [JSON-RPC API][engineapi] under the namespace `engine`
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which is exposed by Geth.
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The `engine` API is authenticated via [JWT](https://jwt.io). If a TTD is set for the given
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network, as is the case for Ropsten, Geth will:
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- Generate a JWT secret under the path `<datadir>/geth/jwtsecret`. This secret is needed
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both by Geth and the CL client.
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- Open HTTP and WS endpoints on the authenticated port 8551.
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This is what it looks like by default:
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```shell
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geth --ropsten --datadir ~/.ropsten
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```
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```terminal
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INFO [05-25|11:04:41.179] Starting Geth on Ropsten testnet...
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...
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WARN [05-25|11:04:41.520] Catalyst mode enabled protocol=eth
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INFO [05-25|11:04:41.627] Generated JWT secret path=/home/user/.ropsten/geth/jwtsecret
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INFO [05-25|11:04:41.628] WebSocket enabled url=ws://127.0.0.1:8551
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INFO [05-25|11:04:41.628] HTTP server started endpoint=127.0.0.1:8551 auth=true prefix= cors=localhost vhosts=localhost
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```
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### Engine API Authentication
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The listening address of the engine API is configurable. It is also possible to
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self-generate the JWT secret and feed the resulting file to Geth. To generate the secret,
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run:
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```shell
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openssl rand -hex 32 | tr -d "\n" > "/tmp/jwtsecret"
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```
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Now configure authentication using Geth flags:
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```shell
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geth --ropsten --datadir ~/.ropsten --authrpc.addr localhost --authrpc.port 8551 --authrpc.vhosts localhost --authrpc.jwtsecret /tmp/jwtsecret
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```
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[engineapi]: https://github.com/ethereum/execution-apis/blob/main/src/engine/specification.md
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[cl-list]: https://ethereum.org/en/developers/docs/nodes-and-clients/#consensus-clients
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