Controlling Logic behind EthersJS FallbackProvider: Ensuring Consistency Across Multiple RPCs
When using EthersJS for managing multiple RPCs, one of the primary concerns is ensuring consistency across different providers. The FallbackProvider is a crucial component in this regard, but its flexibility can sometimes lead to inconsistencies if not properly configured. In this article, we’ll explore how to control the logic behind ethersJs FallbackProvider and address common issues that may arise.
Why is Consistency Important?
In the context of EthersJS, consistency across multiple RPCs is crucial for maintaining a single, unified view of the blockchain state. If one provider has a different quorum (minimum number of signatures required to validate transactions) than another, it can lead to inconsistencies in the final state of the network.
FallbackProvider’s Default Quorum
The FallbackProvider by default uses 4 out of 6 available blockchains (or chains, if you will) to make a decision. This means that if one provider fails or is unresponsive for an extended period, it may fall back on the other providers to make a decision.
Issue: Event when setting a quorum
One common issue with the FallbackProvider is that setting a custom quorum can lead to inconsistent decisions across multiple RPCs. When you set a quorum, EthersJS will use the default blockchain(s) in case another provider falls back on them. This means that if one provider has a higher quorum than others, it may be chosen as the fallback, even if it’s not the correct choice for your specific use case.
Solution: Customizing the FallbackProvider
To control the logic behind ethersJs FallbackProvider and ensure consistency across multiple RPCs, you can customize its behavior. Here are a few strategies to achieve this:
- Override the default quorum
: You can override the default 4-quorum rule by setting a custom quorum for each provider. For example:
const fallbackProvider = new ethers.providers.FallbackProvider({
providers: [ethers.providers.JsonRpcProvider(' // Provider A
ethers.providers.JsonRpcProvider(' // Provider B
},
gasLimit: 1000000,
maxPriorityFeePerGas: 1.5, // adjust the gas limit for each provider
});
In this example, Provider A has a custom quorum of 4, while Provider B falls back to the default 6-quorum.
- Use a quorum-based fallback strategy: You can use a quorum-based approach where you select the provider with the highest quorum when making a decision. For example:
const fallbackProvider = new ethers.providers.FallbackProvider({
providers: [
{
name: 'Provider A',
address: '
gasLimit: 1000000,
maxPriorityFeePerGas: 1.5,
},
{
name: 'Provider B',
address: '
gasLimit: 1000000,
maxPriorityFeePerGas: 1.5,
},
],
fallback: (event, provider) => {
if (provider.quorum > 4) {
// Provider A is chosen as the fallback
return 'Provider A';
} else {
// Provider B is chosen as the fallback
return 'Provider B';
}
},
});
In this example, Provider A has a quorum of 4, so it’s chosen as the fallback when making a decision.
- Use a consensus algorithm: You can use a consensus algorithm like Proof of Stake (PoS) or Delegated Proof of Stake (DPoS) to ensure that multiple providers agree on a quorum. For example:
« `javascript
const fallbackProvider = new ethers.providers.FallbackProvider({
providers: [
{
name: ‘Provider A’,
address: ‘
gasLimit: 1000000,
maxPriorityFeePerGas: 1.