chain_specs.md

title	Polkadot SDK Chain Specifications

Intro

In Polkadot SDK, a chain specification is the collection of information that describes a Polkadot SDK-based blockchain network. For example, the chain specification identifies the network that a blockchain node connects to, the other nodes that it initially communicates with, and the initial state that nodes must agree on to produce blocks.

Chain specs can be provided to a node either through a hard-coded means(see chain_spec.rs), or a generated version(see ./node/res). It is common to write different functions or generate chain spec files to represent different network deployments. E.g. a chain spec by the name of "local.json" might represent a chain spec by the name of local("local" in the case of our network, represents the public devnet, due to timing of release).

Examples

Build "local" chain specification:

./target/release/midnight-node build-spec --disable-default-bootnode > chain-spec.json

Get "raw" version of "local chain specification:

./target/release/midnight-node build-spec --chain chain-spec.json --disable-default-bootnode > chain-spec-raw.json

Start a node based on a chain spec file

./target/release/midnight-node --chain chain-spec-raw.json