Substrate Validator Set Pallet

A Substrate pallet to add/remove authorities/validators using extrinsics, in Substrate-based PoA networks.

Note: Current master is compatible with Substrate monthly-2021-12 tag. For older versions, please see releases/tags.

Demo

To see this pallet in action in a Substrate runtime, watch this video - https://www.youtube.com/watch?v=lIYxE-tOAdw

Setup with Substrate Node Template

Dependencies - runtime/cargo.toml

• Add the module's dependency in the Cargo.toml of your runtime directory. Make sure to enter the correct path or git url of the pallet as per your setup.

• Make sure that you also have the Substrate session pallet as part of your runtime. This is because the validator-set pallet is dependent on the session pallet.

[dependencies.validator-set]
default-features = false
package = 'substrate-validator-set'
git = 'https://github.com/gautamdhameja/substrate-validator-set.git'
version = '4.0.0-dev'

[dependencies.pallet-session]
default-features = false
git = 'https://github.com/paritytech/substrate.git'
tag = 'monthly-2021-12'
version = '4.0.0-dev'

std = [
	...
	'validator-set/std',
	'pallet-session/std',
]

Pallet Initialization - runtime/src/lib.rs

• Import OpaqueKeys in your runtime/src/lib.rs.

use sp_runtime::traits::{
	AccountIdLookup, BlakeTwo256, Block as BlockT, Verify, IdentifyAccount, NumberFor, OpaqueKeys,
};

• Also in runtime/src/lib.rs import the EnsureRoot trait. This would change if you want to configure a custom origin (see below).

	use frame_system::EnsureRoot;

• Declare the pallet in your runtime/src/lib.rs. The pallet supports configurable origin and you can either set it to use one of the governance pallets (Collective, Democracy, etc.), or just use root as shown below. But do not use a normal origin here because the addition and removal of validators should be done using elevated privileges.

parameter_types! {
	pub const MinAuthorities: u32 = 2;
}

impl validator_set::Config for Runtime {
	type Event = Event;
	type AddRemoveOrigin = EnsureRoot<AccountId>;
	type MinAuthorities = MinAuthorities;
}

• Also, declare the session pallet in your runtime/src/lib.rs. Some of the type configuration of session pallet would depend on the ValidatorSet pallet as shown below.

parameter_types! {
	pub const Period: u32 = 2 * MINUTES;
	pub const Offset: u32 = 0;
}

impl pallet_session::Config for Runtime {
	type ValidatorId = <Self as frame_system::Config>::AccountId;
	type ValidatorIdOf = validator_set::ValidatorOf<Self>;
	type ShouldEndSession = pallet_session::PeriodicSessions<Period, Offset>;
	type NextSessionRotation = pallet_session::PeriodicSessions<Period, Offset>;
	type SessionManager = ValidatorSet;
	type SessionHandler = <opaque::SessionKeys as OpaqueKeys>::KeyTypeIdProviders;
	type Keys = opaque::SessionKeys;
	type WeightInfo = ();
	type Event = Event;
}

• Add validator_set, and session pallets in construct_runtime macro. Make sure to add them before Aura and Grandpa pallets and after Balances. Also make sure that the validator_set pallet is added before the session pallet, because it provides the initial validators at genesis, and must initialize first.

construct_runtime!(
	pub enum Runtime where
		Block = Block,
		NodeBlock = opaque::Block,
		UncheckedExtrinsic = UncheckedExtrinsic
	{
		...
		Balances: pallet_balances::{Pallet, Call, Storage, Config<T>, Event<T>},
		ValidatorSet: validator_set::{Pallet, Call, Storage, Event<T>, Config<T>},
		Session: pallet_session::{Pallet, Call, Storage, Event, Config<T>},
		Aura: pallet_aura::{Pallet, Config<T>},
		Grandpa: pallet_grandpa::{Pallet, Call, Storage, Config, Event},
		...
		...
	}
);

Genesis config - chain_spec.rs

• Import opaque::SessionKeys, ValidatorSetConfig, SessionConfig from the runtime in node/src/chain_spec.rs.

use node_template_runtime::{
	AccountId, AuraConfig, BalancesConfig, GenesisConfig, GrandpaConfig,
	SudoConfig, SystemConfig, WASM_BINARY, Signature, 
	opaque::SessionKeys, ValidatorSetConfig, SessionConfig
};

• And then in node/src/chain_spec.rs update the key generation functions.

fn session_keys(aura: AuraId, grandpa: GrandpaId) -> SessionKeys {
	SessionKeys { aura, grandpa }
}

pub fn authority_keys_from_seed(s: &str) -> (AccountId, AuraId, GrandpaId) {
	(
		get_account_id_from_seed::<sr25519::Public>(s),
		get_from_seed::<AuraId>(s),
		get_from_seed::<GrandpaId>(s)
	)
}

• Add genesis config in the chain_spec.rs file for session and validatorset pallets, and update it for Aura and Grandpa pallets. Because the validators are provided by the session pallet, we do not initialize them explicitly for Aura and Grandpa pallets. Order is important, notice that pallet_session is declared after pallet_balances since it depends on it (session accounts should have some balance).

fn testnet_genesis(initial_authorities: Vec<(AccountId, AuraId, GrandpaId)>,
	root_key: AccountId,
	endowed_accounts: Vec<AccountId>,
	_enable_println: bool) -> GenesisConfig {
	GenesisConfig {
		...,
		balances: BalancesConfig {
			balances: endowed_accounts.iter().cloned().map(|k|(k, 1 << 60)).collect(),
		},
		validator_set: ValidatorSetConfig {
			initial_validators: initial_authorities.iter().map(|x| x.0.clone()).collect::<Vec<_>>(),
		},
		session: SessionConfig {
			keys: initial_authorities.iter().map(|x| {
				(x.0.clone(), x.0.clone(), session_keys(x.1.clone(), x.2.clone()))
			}).collect::<Vec<_>>(),
		},
		aura: AuraConfig {
			authorities: vec![],
		},
		grandpa: GrandpaConfig {
			authorities: vec![],
		},
	}
}

Types for Polkadot JS Apps/API

{
  "Keys": "SessionKeys2"
}

Run

Once you have set up the pallet in your node/node-template and everything compiles, follow the steps in docs/local-network-setup.md to run a local network and add validators. Also, watch this video to see this in action - https://www.youtube.com/watch?v=lIYxE-tOAdw.

Extensions

Council-based governance

Instead of using sudo, for a council-based governance, use the pallet with the Collective pallet. Follow the steps in docs/council-integration.md.

Auto-removal of offline validators

When a validator goes offline, it skips its block production slot in Aura and that causes increased block times. Sometimes, we want to remove these offline validators so that the block time can recover to normal. The ImOnline pallet, when added to a runtime, can report offline validators and the ValidatorSet pallet implements the required types to integrate with ImOnline pallet for automatic removal of offline validators. To use the ValidatorSet pallet with the ImOnline pallet, follow the steps in docs/im-online-integration.md.

Disclaimer

This code not audited and reviewed for production use cases. You can expect bugs and security vulnerabilities. Do not use it as-is in real applications.