Appchain Quickstart

AppChain Quickstart

PREVIEW — AppChain packages are in preview. APIs may change between releases.

A Nethereum AppChain is a lightweight, domain-specific extension layer for Ethereum L1/L2. It runs a full EVM, exposes standard JSON-RPC, and supports follower sync with state verification.

When to Use This Skill

• User wants to launch a custom blockchain/chain with .NET
• User needs a sequencer + follower architecture
• User wants persistent blockchain storage with RocksDB
• User wants to sync and verify chain state across nodes
• User mentions AppChain, application chain, or domain-specific chain

Packages

# CLI tool (sequencer/follower server)
dotnet tool install Nethereum.AppChain.Server

# Programmatic usage
dotnet add package Nethereum.AppChain.Sequencer   # AppChainBuilder
dotnet add package Nethereum.CoreChain             # Storage interfaces + in-memory
dotnet add package Nethereum.CoreChain.RocksDB     # RocksDB persistent storage
dotnet add package Nethereum.AppChain.Sync         # Multi-peer sync

Quick Launch (CLI)

Sequencer (produces blocks)

nethereum-appchain \
  --port 8546 \
  --chain-id 420420 \
  --name "MyAppChain" \
  --genesis-owner-key 0xYOUR_PRIVATE_KEY \
  --sequencer-key 0xYOUR_PRIVATE_KEY \
  --block-time 1000

Follower (syncs and verifies)

nethereum-appchain \
  --port 8547 \
  --chain-id 420420 \
  --genesis-owner-address 0xOWNER_ADDRESS \
  --sync-peers http://sequencer:8546 \
  --sync-poll-interval 100

The follower re-executes transactions locally and validates state roots against the sequencer.

Programmatic AppChain (AppChainBuilder)

For embedded usage, testing, or when you need programmatic control:

using Nethereum.AppChain.Sequencer.Builder;

// Simple in-memory chain
var chain = await new AppChainBuilder("TestChain", 420420)
    .WithOperator(privateKey)
    .BuildAsync();

// With RocksDB and custom config
var chain = await new AppChainBuilder("MyChain", 420420)
    .WithOperator(privateKey)
    .WithStorage(StorageType.RocksDb, "./data/mychain")
    .WithBaseFee(0)
    .WithBlockGasLimit(30_000_000)
    .WithOnDemandBlocks()       // Block only when txns arrive
    .WithPrefundedAddresses(new[] { addr1, addr2 })
    .BuildAsync();

Presets

// Gaming — optimized for high-frequency state updates
var chain = await AppChainPresets
    .ForGaming("GameChain", 420420, operatorKey)
    .BuildAsync();

// Testing — in-memory, on-demand blocks
var chain = await AppChainPresets
    .ForTesting("TestChain", 31337, testKey)
    .BuildAsync();

In-Process RPC (No HTTP)

var node = new AppChainNode(chain.AppChain, chain.Sequencer);
var rpcClient = new AppChainRpcClient(node, chainId: 420420);
var web3 = new Web3(new Account(userKey, 420420), rpcClient);

// Use web3 normally — no HTTP overhead
var balance = await web3.Eth.GetBalance.SendRequestAsync(userAddress);

Interact via Nethereum

Once running, connect with standard Nethereum:

using Nethereum.Web3;
using Nethereum.Web3.Accounts;

var account = new Account(privateKey, chainId: 420420);
var web3 = new Web3(account, "http://localhost:8546");

// Genesis owner is pre-funded
var balance = await web3.Eth.GetBalance.SendRequestAsync(account.Address);

// Deploy and interact with contracts — same as any Ethereum network
var receipt = await web3.Eth.GetContractDeploymentHandler<MyContractDeployment>()
    .SendRequestAndWaitForReceiptAsync(new MyContractDeployment { ... });

Storage

In-Memory (development)

using Nethereum.CoreChain.Storage.InMemory;

var blockStore = new InMemoryBlockStore();
var txStore = new InMemoryTransactionStore(blockStore);
var receiptStore = new InMemoryReceiptStore();
var logStore = new InMemoryLogStore();
var stateStore = new InMemoryStateStore();
var trieNodeStore = new InMemoryTrieNodeStore();

RocksDB (production)

using Nethereum.CoreChain.RocksDB;
using Nethereum.CoreChain.RocksDB.Stores;

var options = new RocksDbStorageOptions { DatabasePath = "./chaindata" };
using var manager = new RocksDbManager(options);

var blockStore = new RocksDbBlockStore(manager);
var txStore = new RocksDbTransactionStore(manager, blockStore);
var receiptStore = new RocksDbReceiptStore(manager, blockStore);
var logStore = new RocksDbLogStore(manager);
var stateStore = new RocksDbStateStore(manager);
var trieNodeStore = new RocksDbTrieNodeStore(manager);

DI Registration

services.AddRocksDbStorage("./chaindata");

Sync

Multi-Peer Live Sync

using Nethereum.AppChain.Sync;

var peerManager = new PeerManager(new PeerManagerConfig());
peerManager.AddPeer("http://sequencer:8546");

var syncConfig = new MultiPeerSyncConfig
{
    PollIntervalMs = 100,
    AutoFollow = true,
    RejectOnStateRootMismatch = true
};

var syncService = new MultiPeerSyncService(syncConfig,
    blockStore, txStore, receiptStore, logStore,
    finalityTracker, peerManager, blockReExecutor);

await syncService.StartAsync();

Finality

bool isFinal = await finalityTracker.IsFinalizedAsync(blockNumber);  // L1-anchored
bool isSoft = await finalityTracker.IsSoftAsync(blockNumber);         // Synced, not anchored

Key Decisions

Common Gotchas

• Same genesis = same chain — sequencer and followers must use the same genesis owner address and chain ID
• RocksDB is the default — CLI uses RocksDB unless you pass --in-memory
• One RocksDbManager per path — don't create multiple managers pointing at the same directory
• Port 8546 — AppChain defaults to 8546, not 8545 like Geth

For full documentation, see: https://docs.nethereum.com/docs/application-chain/overview