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chain-spec.md

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Generate custom chain specification

The chain-spec file is essentially a genesis snapshot of your chain's state. It defines the initial set of validators, the initial WASM binary of the runtime, miscellaneous chain metadata, etc.

If you want to join an existing chain, you can skip this step as this only needs to be performed once when bootstrapping the network. The only thing you need from this part is the chain-spec-raw.json file that contains all necessary information for your fresh node to join the existing network and start syncing. You can download this file from here

The initial bootnode needs to generate a chain-spec.json file that contains genesis configuration for the blockchain by running

./target/release/node-template build-spec --disable-default-bootnode > chain-spec.json
{
  "name": "Local Testnet",
  "id": "local_testnet",
  "chainType": "Local",
  "bootNodes": [],
  "telemetryEndpoints": null,
  "protocolId": null,
  "properties": null,
  "consensusEngine": null,
  "codeSubstitutes": {},
  ..
}

Here, the chainType can be set to Local, Development, or Live. The difference between these is that when the type is Local or Development, the chain starts with pre-funded accounts that can interact with the network. The Live type doesn't provide pre-funded accounts by default, you need to set it manually. You may set the name and id fields if you want but note that the id field determines where the chain data will be located on on your computer. For example if id = hello, then the node database, keystore, and other network-related stuff will be located in /tmp/mynode/hello, unless specified otherwise when starting a live node. Therefore, make sure that the aura and grandpa keys are saved under /tmp/mynode/hello/keystore, otherwise you won't be able to validate and produce blocks. Generally there's only two fields that definitely require modification.

The aura field needs to contain all SS58 addresses of the Sr25519 keys generated in the previous steps:

"aura": { 
  "authorities": [
    "5CfBuoHDvZ4fd8jkLQicNL8tgjnK8pVG9AiuJrsNrRAx6CNW",
    "5CXGP4oPXC1Je3zf5wEDkYeAqGcGXyKWSRX2Jm14GdME5Xc5"
  ]
}

The grandpa field needs to contain all SS58 addresses of the Ed25519 keys generated in the previous steps:

"grandpa": {
  "authorities": [
    [
      "5CuqCGfwqhjGzSqz5mnq36tMe651mU9Ji8xQ4JRuUTvPcjVN",
      1
    ],
    [
      "5DpdMN4bVTMy67TfMMtinQTcUmLhZBWoWarHvEYPM4jYziqm",
      1
    ]
  ]
},

The second element after the address is the voting weight of the nodes, here set to 1 for both members.

After the specs are finalized, the chain-spec.json file needs to be converted to raw format by running

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

Finally, make sure that every node operator receives the same chain-spec-raw.json file.