Putting All Together

This chapter is a capstone. We build one small node framework once, then apply it to two very different domains.

The contrast is the point:

• Blockchain: decentralized, gossip-driven, eventually consistent, heavy validation.
• Order book: deterministic, totally ordered, strict concurrency boundaries, strict price-time priority.

What “together” means

We are reusing the exact building blocks from earlier chapters:

• Structured task lifecycle with JoinSet: spawn long-running tasks, await them, and shut down cleanly.
• Framed networking with LengthDelimitedCodec: no partial-read protocol bugs.
• Resilience as middleware with tower::ServiceBuilder: timeout, retry, rate_limit, load_shed.
• Observability with tracing: spans and structured events.
• Client-facing RPC with tonic: typed gRPC APIs.

Shared repository layout

crates/
  nodekit/
  blockchain_node/
  orderbook_node/

• nodekit/: runtime bootstrap, config, shutdown, tracing setup, transport helpers, and common metrics labels.
• blockchain_node/: gossip, sync, mempool, validation, block production.
• orderbook_node/: sequencing, matching, event log replication, market data streaming.

From here on, we will keep one rule: reuse the same skeleton, swap domain logic.