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Cumulus ☁️

A set of tools for writing Substrate-based Polkadot parachains. Refer to the included overview for architectural details, and the Cumulus workshop for a hand-holding walkthrough of using these tools.

It's easy to write blockchains using Substrate, and the overhead of writing parachains' distribution, p2p, database, and synchronization layers should be just as low. This project aims to make it easy to write parachains for Polkadot by leveraging the power of Substrate.

Cumulus clouds are shaped sort of like dots; together they form a system that is intricate, beautiful and functional.

Consensus

cumulus-consensus is a consensus engine for Substrate that follows a Polkadot relay chain. This will run a Polkadot node internally, and dictate to the client and synchronization algorithms which chain to follow, finalize, and treat as best.

Collator

A Polkadot collator for the parachain is implemented by cumulus-collator.

Rococo 👑

Rococo is the testnet for parachains. It currently runs the parachains Tick, Trick and Track.

Rococo is an elaborate style of design and the name describes the painstaking effort that has gone into this project. Tick, Trick and Track are the German names for the cartoon ducks known to English speakers as Huey, Dewey and Louie.

Build & Launch Rococo Collators

Collators are similar to validators in the relay chain. These nodes build the blocks that will eventually be included by the relay chain for a parachain.

To run a Rococo collator you will need to compile the following binary:

cargo build --release --locked -p polkadot-collator

Otherwise you can compile it with Parity CI docker image:

docker run --rm -it -w /shellhere/cumulus \
                    -v $(pwd):/shellhere/cumulus \
                    paritytech/ci-linux:production cargo build --release --locked -p polkadot-collator
sudo chown -R $(id -u):$(id -g) target/

If you want to reproduce other steps of CI process you can use the following guide.

Once the executable is built, launch collators for each parachain (repeat once each for chain tick, trick, track):

./target/release/polkadot-collator --chain $CHAIN --validator

Parachains

The parachains of Rococo all use the same runtime code. The only difference between them is the parachain ID used for registration with the relay chain:

  • Tick: 100
  • Trick: 110
  • Track: 120

The network uses horizontal message passing (HRMP) to enable communication between parachains and the relay chain and, in turn, between parachains. This means that every message is sent to the relay chain, and from the relay chain to its destination parachain.

Launch a local setup including a Relay Chain and a Parachain

Launch the Relay Chain

# Compile Polkadot with the real overseer feature
git clone https://github.com/paritytech/polkadot
cargo build --release

# Generate a raw chain spec
./target/release/polkadot build-spec --chain rococo-local --disable-default-bootnode --raw > rococo-local-cfde.json

# Alice
./target/release/polkadot --chain rococo-local-cfde.json --alice --tmp

# Bob (In a separate terminal)
./target/release/polkadot --chain rococo-local-cfde.json --bob --tmp --port 30334

Launch the Parachain

# Compile
git clone https://github.com/paritytech/cumulus
cargo build --release

# Export genesis state
# --parachain-id 200 as an example that can be chosen freely. Make sure to everywhere use the same parachain id
./target/release/polkadot-collator export-genesis-state --parachain-id 200 > genesis-state

# Export genesis wasm
./target/release/polkadot-collator export-genesis-wasm > genesis-wasm

# Collator1
./target/release/polkadot-collator --collator --tmp --parachain-id <parachain_id_u32_type_range> --port 40335 --ws-port 9946 -- --execution wasm --chain ../polkadot/rococo-local-cfde.json --port 30335

# Collator2
./target/release/polkadot-collator --collator --tmp --parachain-id <parachain_id_u32_type_range> --port 40336 --ws-port 9947 -- --execution wasm --chain ../polkadot/rococo-local-cfde.json --port 30336

# Parachain Full Node 1
./target/release/polkadot-collator --tmp --parachain-id <parachain_id_u32_type_range> --port 40337 --ws-port 9948 -- --execution wasm --chain ../polkadot/rococo-local-cfde.json --port 30337

Register the parachain

image

Build the docker image

After building polkadot-collator with cargo or with Parity docker image as documented in this chapter, the following will allow producting a new docker image where the compiled binary is injected:

./docker/scripts/build-injected-image.sh

You may then start a new contaier:

docker run --rm -it $OWNER/$IMAGE_NAME --collator --tmp --parachain-id 1000 --execution wasm --chain /specs/westmint.json