Running a private Ethereum network in a Docker container

Find the code at Ethereum Private Network on GitHub.

To define a network, we need:

• a unique genesis file
• the Go Ethereum client geth

Other peers can join the network if and only if they share the same genesis file.

Genesis block

The genesis block defines a bunch of parameters each peer must agree on if they want to join the network.

The docker file stores the following file in the directory /app/:

{
    "config": {
        "chainId": 99,
        "homesteadBlock": 0,
        "eip150Block": 0,
        "eip150Hash":"0x0000000000000000000000000000000000000000000000000000000000000000",
        "eip155Block": 0,
        "eip158Block": 0,
        "byzantiumBlock": 0,
        "constantinopleBlock": 0,
        "petersburgBlock":0
    },
    "nonce": "0x1200abc184050099",
    "timestamp": "0x00",
    "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "extraData": "0x00",
    "gasLimit": "0x4c4b40",
    "difficulty": "0x0400",
    "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "coinbase": "0x0000000000000000000000000000000000000000",
    "alloc": {}
}

The notable fields are:

• chainId, the network id
• difficulty
• fields in the config section
• alloc

Network id

The network id is a positive number. Avoid using 1, 2, 3 or 4, as they are reserved to existing public network:

• 1 main Ethereum network
• 2 Morden test network
• 3 Ropsten test network
• 4 Rinkeby test network
• 5 Goerly test network
• 42 Kovan test network
• 1337 Geth private chains

We set our private network id to 99 with

"chainId": 99

Difficulty

We set the difficulty to 1024 (0x400 in hexadecimal) with:

"difficulty": "0x0400"

This will enable fast mining. geth will eventualy adjust this value overtime. The default value, used in the main net, is 0x400000000.

Config

The config section defines the consensus protocols used, and at which block the network should start using each consensus protocol. It is in fact possible to switch from a consensus protocol to another, starting from a defined block, and have therefore a fork.

More than defining the beginning of a network, the genesis block defines the progression of protocols in a network.

Pre-allocated ethereum

The genesis block can defined the balance of one or more accounts, specifying the number of wei to pre-allocate to each account:

"alloc": {
        "0x1a7750aba798ea108ebc1873eab839910212855b": {
            "balance": "51000000000000000000"
        }
    }

We won’t pre-allocate any ethereum, as we will be able to easily mine them, so our genesis block contains:

"alloc": { }

Start the network

To start the network, init it:

geth \
     --datadir /app/network99 \
     init \
     /app/genesis99.json

then connect to it with:

geth \
     --datadir /app/network99 \
     --networkid 99

Operations

Checkout the GitHub repo https://github.com/arialdomartini/private-ethereum: it contains a docker-compose bundle to setup a one-node Ethereum private network, and as well a sample session to interactively create accounts, mine blocks and make transactions in an Ethereum console.