# Prysm Client Interoperability Guide

This README details how to setup Prysm for interop testing for usage with other Ethereum consensus clients.

## Installation & Setup

1. Install [Bazel](https://docs.bazel.build/versions/master/install.html) **(Recommended)**
2. `git clone https://github.com/prysmaticlabs/prysm && cd prysm`
3. `bazel build //...`

## Starting from Genesis

Prysm supports a few ways to quickly launch a beacon node from basic configurations:

- `NumValidators + GenesisTime`: Launches a beacon node by deterministically generating a state from a num-validators flag along with a genesis time **(Recommended)**
- `SSZ Genesis`: Launches a beacon node  from a .ssz file containing a SSZ-encoded, genesis beacon state

## Generating a Genesis State

To setup the necessary files for these quick starts, Prysm provides a tool to generate a `genesis.ssz` from
a deterministically generated set of validator private keys following the official interop YAML format 
[here](https://github.com/ethereum/eth2.0-pm/blob/master/interop/mocked_start).

You can use `bazel run //tools/genesis-state-gen` to create a deterministic genesis state for interop.

### Usage

- **--genesis-time** uint: Unix timestamp used as the genesis time in the generated genesis state (defaults to now)
- **--num-validators** int: Number of validators to deterministically include in the generated genesis state
- **--output-ssz** string: Output filename of the SSZ marshaling of the generated genesis state
- **--config-name=interop** string: name of the beacon chain config to use when generating the state. ex mainnet|minimal|interop

The example below creates 64 validator keys, instantiates a genesis state with those 64 validators and with genesis unix timestamp 1567542540,
and finally writes a ssz encoded output to ~/Desktop/genesis.ssz. This file can be used to kickstart the beacon chain in the next section. When using the `--interop-*` flags, the beacon node will assume the `interop` config should be used, unless a different config is specified on the command line.

```
bazel run //tools/genesis-state-gen -- --config-name interop --output-ssz ~/Desktop/genesis.ssz --num-validators 64 --genesis-time 1567542540
```

## Launching a Beacon Node + Validator Client

### Launching from Pure CLI Flags

Open up two terminal windows, run:

```
bazel run //beacon-chain -- \
--bootstrap-node= \
--deposit-contract 0x8A04d14125D0FDCDc742F4A05C051De07232EDa4 \
--datadir=/tmp/beacon-chain-interop \
--force-clear-db \
--min-sync-peers=0 \
--interop-num-validators 64 \
--interop-eth1data-votes
```

This will deterministically generate a beacon genesis state and start
the system with 64 validators and the genesis time set to the current unix timestamp.
Wait a bit until your beacon chain starts, and in the other window:

```
bazel run //validator -- --keymanager=interop --keymanageropts='{"keys":64}'
```

This will launch and kickstart the system with your 64 validators performing their duties accordingly.

### Launching from `genesis.ssz`

Assuming you generated a `genesis.ssz` file with 64 validators, open up two terminal windows, run:

```
 bazel run //beacon-chain -- \
--bootstrap-node= \
--deposit-contract 0x8A04d14125D0FDCDc742F4A05C051De07232EDa4 \
--datadir=/tmp/beacon-chain-interop \
--force-clear-db \
--min-sync-peers=0 \
--interop-genesis-state /path/to/genesis.ssz \
--interop-eth1data-votes
```

Wait a bit until your beacon chain starts, and in the other window:

```
bazel run //validator -- --keymanager=interop --keymanageropts='{"keys":64}'
```

This will launch and kickstart the system with your 64 validators performing their duties accordingly.
