BA-09 · LESSON 09

Full node architecture

KEY DEFINITIONS

Terms used in this lesson

RPC: Remote procedure call: the command interface applications use to ask a Bitcoin node to perform operations or return state.
ZMQ: ZeroMQ: a messaging interface Bitcoin Core can use to notify applications about new blocks and transactions.
UTXO: Unspent transaction output: one discrete chunk of bitcoin that can be used as a transaction input.
Proof-of-work target: The maximum header-hash value accepted for a block; lowering it makes valid hashes harder to find.

Connect peers, message parsing, validation, mempool, block index, chainstate, wallet, RPC, ZMQ, indexes, pruning, and reorg handling in one system map.

35 min Difficulty 3/5 Not started

VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · full node architectureA full node separates untrusted input, validation, stores, and interfacesSelect any state to inspect its exact role.

RELATIONSHIP MAPOrdered mechanism flow

01
PEERSBounded messages
The peer layer supplies untrusted transactions, headers, blocks, and requests.
02
VALIDATIONConsensus and policy checks
Objects earn access to later stores only after the applicable checks.
03
TENTATIVELocal mempool
Unconfirmed policy state can differ between nodes without changing consensus.
04
CONFIRMEDBlock index, chainstate, and undo data
Confirmed UTXOs advance and roll back through atomic block operations.
05
INTERFACESWallet, RPC, ZMQ, indexes
Applications query and reconcile node state rather than becoming authorities.

Rule shown: Only locally validated block connection and disconnection may change active chainstate.

STAGE 1 OF 5PEERS: Bounded messages

The peer layer supplies untrusted transactions, headers, blocks, and requests.

Governing relationship: Only locally validated block connection and disconnection may change active chainstate. Complete path: 1. PEERS, Bounded messages. The peer layer supplies untrusted transactions, headers, blocks, and requests. 2. VALIDATION, Consensus and policy checks. Objects earn access to later stores only after the applicable checks. 3. TENTATIVE, Local mempool. Unconfirmed policy state can differ between nodes without changing consensus. 4. CONFIRMED, Block index, chainstate, and undo data. Confirmed UTXOs advance and roll back through atomic block operations. 5. INTERFACES, Wallet, RPC, ZMQ, indexes. Applications query and reconcile node state rather than becoming authorities.

1. State transitionWhat exists, what changes, and what results

BEFORE

Peer A announces block B while the wallet and an indexer are running.

MECHANISM

Peer discovery and connections feed a message parser with size, command, checksum, timeout, and resource controls. No remote peer can directly write trusted chainstate.

AFTER

Architecture is safest when data sources, validation, tentative state, confirmed state, storage, and application interfaces remain explicit.

Text equivalent: Starting from Peer A announces block B while the wallet and an indexer are running. The mechanism begins when Peer discovery and connections feed a message parser with size, command, checksum, timeout, and resource controls. No remote peer can directly write trusted chainstate. The resulting lesson is Architecture is safest when data sources, validation, tentative state, confirmed state, storage, and application interfaces remain explicit.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 5

Bound the peer boundary

Peer discovery and connections feed a message parser with size, command, checksum, timeout, and resource controls. No remote peer can directly write trusted chainstate.

Complete path: 1. Bound the peer boundary: Peer discovery and connections feed a message parser with size, command, checksum, timeout, and resource controls. No remote peer can directly write trusted chainstate. 2. Route objects to validation: Transactions receive syntax, consensus precondition, conflict, fee, and relay-policy checks. Headers receive linkage, target, work, and time checks. Blocks receive full transaction and contextual validation. 3. Keep stores distinct: Block files store bytes, block index stores branch metadata, mempool stores unconfirmed candidates, chainstate stores confirmed spendable outputs, and undo data restores a prior chainstate during disconnection. 4. Expose controlled interfaces: RPC requests local state or actions. ZMQ publishes non-durable event notifications. Wallets construct and track transactions. Optional indexes accelerate queries but do not replace validation. 5. Change storage without changing rules: Pruning removes old raw files only after validation. AssumeUTXO can bootstrap from a recognized committed snapshot while background validation reproduces history. Neither permits arbitrary state.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

Only validation can authorize changes to active chainstate; every interface and derived store must be recoverable from trusted node state and handle reorgs.

CHANGED CONDITION

An RPC caller, wallet database, ZMQ subscriber, peer count, block-file record, or optional index cannot make an invalid block part of active chainstate.

Important distinction: Bitcoin Core is one blockchain database that wallets and peers edit. It contains several stores and interfaces. The active UTXO state changes only through locally validated block connection and disconnection.

Text equivalent: The accepted path is enforced by Only validation can authorize changes to active chainstate; every interface and derived store must be recoverable from trusted node state and handle reorgs. If the required condition changes, An RPC caller, wallet database, ZMQ subscriber, peer count, block-file record, or optional index cannot make an invalid block part of active chainstate.

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Learn the idea

A full node is a collection of bounded subsystems connected by validation rules. The peer layer receives untrusted messages. Validation produces accepted transactions, headers, and blocks. The mempool keeps local unconfirmed policy state. The block index records branch metadata. Chainstate stores the active UTXO set. Wallets, RPC, ZMQ, optional indexes, pruning, and snapshots consume or expose selected views without becoming consensus authorities.

GUIDED EXPLANATION1/5 ideas inspected

Bound the peer boundary

Peer discovery and connections feed a message parser with size, command, checksum, timeout, and resource controls. No remote peer can directly write trusted chainstate.

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“Bitcoin Core is one blockchain database that wallets and peers edit.”

It contains several stores and interfaces. The active UTXO state changes only through locally validated block connection and disconnection.

FINISH LEARNING FIRST

The questions unlock after every required learning activity

Inspect every guided idea, open the worked example, rebuild its mechanism, and complete the deterministic lesson tool. Your progress is saved automatically.