Ethereum (and compatible) Blockchains

A blockchain is:

• a data structure
• used in distributed systems
• where the nodes are not trusted
• but still need to reach consensus
• about what events are recorded and in what order

The most common use case so far was to use blockchain to hold a distributed ledger of transactions. Bitcoin was the first blockchain to become popular, and is used (mostly) for keeping the record of value transfers between different parties.

Ethereum came later and introduced the idea of smart contracts, which are basically pieces of code that are stored and executed on the nodes that manage the blockchain. This expanded the usage and utility of blockchain as a technology and allowed many novel use-cases, such as decentralized finance (DeFi), decentralized naming service exchanges, cryptocurrencies whose supply is algorithmically controlled as to keep its value close to a fiat currency (commonly called stable tokens), games on the blockchain, and much more.

The Ethereum blockchain also led to an explosion of alternative systems that use the same language for smart contracts, but use different technologies for the consensus mechanisms. One example would be the Binance Smart Chain, which uses a different approach to how the nodes reach consensus. It makes the trade-off of having less nodes validating the transactions in the network to achieve a better performance in terms of network capacity.

There are also other projects that want to scale the Ethereum network by taking some of the transaction off the main chain and only using the Ethereum blockchain to secure the final state of the transactions. These so-called "Layer-2" projects oftentimes also have nodes that use the same interface as the common Ethereum nodes.

Finally, another type of blockchain-based system that are compatible with Ethereum are sidechains, such as xDAI and Polygon. Sidechains do not rely on Ethereum's base layer for managing any of the transactions and are run independently, but they still can execute the same types of smart contracts and (currently) are much cheaper to execute transactions.

The most interesting thing for you as a Hub20 operator is the fact that you can connect to any blockchain that is compatible to Ethereum and that uses the RPC API.

Connecting to a blockchain

Usually the software libraries and applications that can interact with Ethereum API are called "Web3-compliant". In the docs, we will refer to any system that provides a Ethereum-compatible RPC API as "web3 nodes" or "web3 provider".

When you first start Hub20, it will not have any information about the different blockchains and it won't have any information about which provider to use to connect to them.

As a Hub Operator, it is up to you to set up the Chain and Web3Provider records. This can be done in two different ways:

Through the admin interface

If you have set up the admin application, you can check the blockchain section and click to add a new chain. You will need to know the chain Id (which is unique among the different blockchains, and you need to know beforehand) and provide a name.

After you created the chain entry, you will need to add a "web3 provider" entry. If you are connecting to Ethereum, you will have to provide your own node or use a service like Infura. For the other types of systems, there is usually a public RPC node that can be used.

You can have many different web3 providers for any given chain on the database, but only one of them should be active at the same time.

Through the command line

If you are managing your system through the command line, yo have the following commands to help you with registration of chains / web3 providers:

• load_chain_data will collect information all chains currently provided by chainlist.org.
• the register_blockchain command can be used both to create a new chain entry and add the web3 provider in one single step.

Verifying your connection to the blockchains

For obvious reasons, the processes that interact with the blockchain run outside of the web application process. If your hub is connected to the web3 provider, you should be able to observe the following:

• The run_payment_providers process is running and periodically (every second) checking the updates for new transactions and blocks.
• The run_payment_processors process will look at every open payment route to query for transactions received at allocated address.

On the web side of things, you should be able to track the status of the blockchain on the /networks/<network_id>/status URL. This endpoint will list chain-specific information (current block height, connection status, etc)