Edit

Create a Custom Chain Spec

Now that each participant has their own keys generated, you're ready to create a custom chain specification. We will use this custom chain spec instead of the built-in local spec that we used previously.

In this example we will create a two-node network, but the process generalizes to more nodes in a straight-forward manner.

Create a Chain Specification

Last time around, we used --chain local which is a predefined "chain spec" that has Alice and Bob specified as validators along with many other useful defaults.

Rather than writing our chain spec completely from scratch, we'll just make a few modifications to the one we used before. To start, we need to export the chain spec to a file named customSpec.json. Remember, further details about all of these commands are available by running node-template --help.

# Export the local chainspec to json
$ ./target/release/node-template build-spec --disable-default-bootnode --chain local > customSpec.json
2020-05-28 13:29:05 Building chain spec

The file we just created contains several fields, and you can learn a lot by exploring them. By far the largest field is a single binary blob that is the Wasm binary of our runtime. It is part of what you built earlier when you ran the cargo build --release command.

The portion of the file we're interested in is the Aura authorities used for creating blocks, indicated by "aura" field below, and GRANDPA authorities used for finalizing blocks, indicated by "grandpa" field. That section looks like this

{
  //-- snip --
  "genesis": {
    "runtime": {
      "system": {
        "changesTrieConfig": null
        //-- snip --
      },
      "palletAura": {
        "authorities": [
          "5FfBQ3kwXrbdyoqLPvcXRp7ikWydXawpNs2Ceu3WwFdhZ8W4",
          "5FHneW46xGXgs5mUiveU4sbTyGBzmstUspZC92UhjJM694ty"
        ]
      },
      "palletGrandpa": {
        "authorities": [
          [
            "5G9NWJ5P9uk7am24yCKeLZJqXWW6hjuMyRJDmw4ofqxG8Js2",
            1
          ],
          [
            "5GoNkf6WdbxCFnPdAnYYQyCjAKPJgLNxXwPjwTh6DGg6gN3E",
            1
          ]
        ]
      },
      //-- snip --
    }
  }
}

These instructions are written for the node template. They will work with other Substrate-based nodes with few modifications. In Substrate nodes that include the session pallet. You should leave the Aura and Grandpa configs empty and instead insert this information in the session config. All of this is demonstrated in the chain spec you export from your desired node.

The format for the grandpa data is more complex because the grandpa protocol supports weighted votes. In this case we have given each validator a weight of 1.

All we need to do is change the authority addresses listed (currently Alice and Bob) to our own addresses that we generated in the previous step. The sr25519 addresses go in the aura section, and the ed25519 addresses in the grandpa section. You may add as many validators as you like. For additional context, read about keys in Substrate.

Validators should not share the same keys, even for learning purposes. If two validators have the same keys, they will produce conflicting blocks.

Once the chain spec is prepared, convert it to a "raw" chain spec. The raw chain spec contains all the same information, but it contains the encoded storage keys that the node will use to reference the data in its local storage. Distributing a raw spec ensures that each node will store the data at the proper storage keys.

$ ./target/release/node-template build-spec --chain=customSpec.json --raw --disable-default-bootnode > customSpecRaw.json
2020-05-28 13:31:37 Building chain spec

Finally share the customSpecRaw.json with your all the other validators in the network.

A single person should create the chain spec and share the resulting customSpecRaw.json file with their fellow validators.

Because Rust -> Wasm optimized builds aren't "reproducible", each person will get a slightly different Wasm blob which will break consensus if each participant generates the file themselves.