Custom Runtime¶

Introduction¶

For teams working on an existing Substrate framework project, it will be necessary to include some required modules and configurations into the runtime. This will ensure that the existing runtime can gracefully become a Tanssi appchain runtime, aligning with the protocol rules.

Failing to do so might lead to reduced interoperability and unnecessary exposure to vulnerabilities.

Minimum Requirements¶

Already existing Substrate runtimes need to implement at least the framework for communicating within the Tanssi ecosystem, along with Tanssi-specific modules.

Nevertheless, teams might have already implemented certain modules that can collide with some functionalities related to Tanssi, for example, block production, block authority assignment, and consensus.

The following modules are included by default in many popular templates and must be removed along with their configuration:

Authorship: pallet_authorship = 20,
CollatorSelection: pallet_collator_selection = 21,
Session: pallet_session = 22,
Aura: pallet_aura = 23,
AuraExt: cumulus_pallet_aura_ext = 24,

In any case, make sure to check your runtime and remove all the modules that might interfere with the block production as a service feature before starting the registration process.

Integrating Your Stand-Alone Chain¶

If your existing runtime is set up as a stand-alone chain, you'll need to add a consensus mechanism to integrate into the Tanssi ecosystem. Check any of the available templates in the Tanssi repository for a reference setup or the framework documentation.

Adding Tanssi Protocol Support¶

To support the Tanssi protocol, it will be necessary to add the modules through the following steps:

1. Include the dependencies in the Cargo.toml manifesto (usually located in the root folder). Open the Cargo.toml file and add the modules in the dependencies section

   [dependencies]
   ...
   pallet-cc-authorities-noting = { 
       git = "https://github.com/moondance-labs/tanssi", 
       branch = "master", default-features = false 
   }
   pallet_authorities_noting = {
       git = "https://github.com/moondance-labs/moonkit",
       branch = "tanssi-polkadot-v0.9.43", default-features = false
   }
   ...
   

2. Configure the modules. Open the file lib.rs located in the folder */runtime/src and add the configuration for both modules:

   impl pallet_author_inherent::Config for Runtime {
       type AuthorId = NimbusId;
       type AccountLookup = tp_consensus::NimbusLookUp;
       type CanAuthor = pallet_cc_authorities_noting::CanAuthor<Runtime>;
       type SlotBeacon = tp_consensus::AuraDigestSlotBeacon<Runtime>;
       type WeightInfo = 
           pallet_author_inherent::weights::SubstrateWeight<Runtime>;
   }
   
   impl pallet_cc_authorities_noting::Config for Runtime {
       type RuntimeEvent = RuntimeEvent;
       type SelfParaId = parachain_info::Pallet<Runtime>;
       type RelayChainStateProvider = 
           cumulus_pallet_parachain_system::RelaychainDataProvider<Self>;
       type AuthorityId = NimbusId;
       type WeightInfo = 
           pallet_cc_authorities_noting::weights::SubstrateWeight<Runtime>;
   }
   

   Note that this configuration is agnostic from the use case

3. Declare the modules as part of the runtime. In the same lib.rs file, located in the folder */runtime/src, add the modules to the construction of the runtime:

   construct_runtime!(
   pub enum Runtime where
       Block = Block,
       NodeBlock = opaque::Block,
       UncheckedExtrinsic = UncheckedExtrinsic,
   {
       ...
       // Tanssi appchain
       AuthoritiesNoting: pallet_cc_authorities_noting = 50,
       AuthorInherent: pallet_author_inherent = 51,
       ...
   }
   

4. Make sure your Header is configured as follows:

   type Header = generic::Header<BlockNumber, BlakeTwo256>;
   /// An index to a block.
   pub type BlockNumber = u32; 
   

5. Add the block executor, to allow the validators in the relay chain to check that the authors are the block producers assigned by Tanssi (and not a malicious actor)

   cumulus_pallet_parachain_system::register_validate_block! {
       Runtime = Runtime,
       BlockExecutor = pallet_author_inherent::BlockExecutor::<Runtime, Executive>
       CheckInherents = CheckInherents,
   }