lighthouse/validator_client/README.md

Lighthouse Validator Client

The Validator Client (VC) is a stand-alone binary which connects to a Beacon Node (BN) and fulfils the roles of a validator.

Roles

The VC is responsible for the following tasks:

• Requesting validator duties (a.k.a. shuffling) from the BN.
• Prompting the BN to produce a new block, when a validators block production duties require.
• Completing all the fields on a new block (e.g., RANDAO reveal, signature) and publishing the block to a BN.
• Prompting the BN to produce a new shard atteststation as per a validators duties.
• Ensuring that no slashable messages are signed by a validator private key.
• Keeping track of the system clock and how it relates to slots/epochs.

The VC is capable of managing multiple validators in the same process tree.

Implementation

This section describes the present implementation of this VC binary.

Services

Each validator is represented by two services, one which tracks the validator duties and another which performs block production duties.

A separate thread is maintained for each service, for each validator. As such, a single validator utilises three (3) threads (one for the base VC and two for each service) and two validators utilise five (5) threads.

DutiesManagerService

Polls a BN and requests validator responsibilities, as well as a validator index. The outcome of a successful poll is a EpochDuties struct:

EpochDuties {
	validator_index: u64,
	block_prodcution_slot: u64,
}

This is stored in the EpochDutiesMap, a HashMap mapping epoch -> EpochDuties.

BlockProducerService

Polls the system clock and determines if a block needs to be produced. Reads from the EpochDutiesMap maintained by the DutiesManagerService.

If block production is required, performs all the necessary duties to request, complete and return a block from the BN.

Configuration

Validator configurations are stored in a separate data directory from the main Beacon Node binary. The validator data directory defaults to: $HOME/.lighthouse-validator, however an alternative can be specified on the command line with --datadir.

The configuration directory structure looks like:

~/.lighthouse-validator
└── validators
    ├── 3cf4210d58ec
    │   └── private.key
    ├── 9b5d8b5be4e7
    │   └── private.key
    └── cf6e07188f48
        └── private.key

Where the hex value of the directory is a portion of the validator public key.

Validator keys must be generated using the separate accounts_manager binary, which will place the keys into this directory structure in a format compatible with the validator client.

The chain specification (slot length, BLS domain, etc.) defaults to foundation parameters, however is temporary and an upgrade will allow these parameters to be read from a file (or initialized on first-boot).

BN Communication

The VC communicates with the BN via a gRPC/protobuf connection.