Hacking Decentralized RPC with Fluence

Overview

Running blockchain nodes to support your dApps' read and write requirements to/from a node tends to be rather resource intensive. Not surprisingly, Web3 developers have been flocking toward integrating their dApps with hosted blockchain JSON-RPC gateways. Alas, centralized "RPC as SaaS" introduces bottlenecks challenging the availability, reliability and Web3 ethos of dApps while quite often raising the exit barriers by providing custom API overlays to the EVM JSON-RPC API convention.

To accelerate dApp developers ability to utilize decentralized RPC in their dApps, Fluence is providing a decentralized RPC (fRPC) substrate, i.e., a starter kit that includes a gateway to bridge HTTP and Aqua, a Wasm service to connect to RPC endpoints and Aqua scripts implementing basic availability, failover and verification algorithms. See Figure 1.

Figure 1: Stylized fRPC Workflow With dAPP

    sequenceDiagram

    participant A as dAPP
    participant G as fRPC Gateway
    participant N as Fluence network
    participant R as RPC endpoints

    A ->> G: dApp HTTP request
    G ->> G: map HTTP to Aqua request
    G ->> G: select algorithm (failover, round robin, quorum, etc.)
    G ->> N: Aqua call to network peer(s)
    N ->> R: HTTP call to RPC endpoint(s)
    R ->> N: Response or timeout
    alt response
      N ->> G: response to gateway
      G ->> A: response to dApp  
    else timeout
      loop over endpoint urls
        N ->> R: try another request
        alt response
          N ->> G: response to gateway
          G ->> A: response to dApp -- break
        end
      end
      G ->> G: timeout 
      G ->> A: no response error
    end

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fRPC substrate allows existing dApps to be upgraded to decentralized RPC while not requiring any changes to their frontend other than changing the HTTP transport url and making it easy to implement more complex control algorithms. Moreover, fRPC substrate components are highly customizable allowing developers to quickly and easily extend the substrate to fit their dApps' needs and to improve the fRPC ecosystem with improved services and algorithms. To this end, Fluence Labs is sponsoring fRPC themed hackathons throughout 2023.

Upcoming Fluence hackathons with fRPC bounties:

• ETHDenver 2023. See Fluence events and bounty repo for more info.

Quickstart

Clone the repo, if you haven't done so already, and in the gateway directory, install the dependencies:

npm i

If you don't have Fluence CLI installed, do:

npm -g i @fluencelabs/[email protected]

Before you proceed, you should have, say, three RPC endpoint urls, e.g., Infura, Alchemy and QuickNode, for the same EVM-based chain you are using in your dAPP. Update the configs/quickstart_config.json by providing your endpoint urls and ignore the rest of the parameters for now:

{
  "providers": [
    "<replace with your url_1/api-key>",   // <- replace
    "<replace with your url_2/api-key>",   // <- replace
    "<replace with your url_3/api-key>"    // <- replace and maybe add more
  ],
  "mode": "round-robin",
  "relay": "/dns4/stage.fluence.dev/tcp/19002/wss/p2p/12D3KooWMigkP4jkVyufq5JnDJL6nXvyjeaDNpRfEZqQhsG3sYCU",
  "serviceId": "e9e32b0b-3b19-4bdd-b1da-f5ff9cc0357f",
  "port": 3000,
  "counterServiceId": null,
  "counterPeerId": null,
  "quorumServiceId": null,
  "quorumPeerId": null,
  "quorumNumber": null
}

Now start the gateway:

npm run run configs/quickstart_config.json
> @fluencelabs/[email protected] run
> fluence aqua -i aqua/ -o aqua-compiled/ --js && node src/index.js configs/my_quickstart_config.json

# Compiling...
Result /Users/bebo/localdev/fRPC-Substrate/gateway/aqua-compiled/rpc.js: compilation OK (10 functions, 4 services)
Result /Users/bebo/localdev/fRPC-Substrate/gateway/aqua-compiled/rpc.d.ts: compilation OK (10 functions, 4 services)
Result /Users/bebo/localdev/fRPC-Substrate/gateway/aqua-compiled/rpc.js: compilation OK (10 functions, 4 services)
Result /Users/bebo/localdev/fRPC-Substrate/gateway/aqua-compiled/rpc.d.ts: compilation OK (10 functions, 4 services)

Running server...
Server was started on port 3000

With the gateway ready for action, all you have to do is change your dApps HTTP transport url to http://127.0.0.1:3000 and keep using your dApp as usual. In the absence of a dAPP, we can interact with the gateway from the command line:

curl http://127.0.0.1:3000  \
    -X POST \
    -H "Content-Type: application/json" \
    -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params": [],"id":100}'

{"jsonrpc":"2.0","id":100,"result":"0x82b950"

# with the corresponding gateway log output
Receiving request 'eth_blockNumber'
peerId: 12D3KooWKDnWpCLPJrycSevracdEgGznfDPwG1g5CWbt8uccdL79
Counter: 1
Worker used: "12D3KooWKPcNwR6EMq3sqm4sKtUKmZbMhPQ2dk1zr8YNgjdu9Xqn"
Call will be to : https://eth-goerli.g.alchemy.com/v2/<your api key>

Since we have specified round-robin in our config file and have more than one endpoint url in play, re-running the json-rpc call should result in a different endpoint selection:

curl http://127.0.0.1:3000  \
    -X POST \
    -H "Content-Type: application/json" \
    -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params": [],"id":100}'

{"jsonrpc":"2.0","id":100,"result":"0x82b956"

# with the corresponding gateway log output

Receiving request 'eth_blockNumber'
peerId: 12D3KooWKDnWpCLPJrycSevracdEgGznfDPwG1g5CWbt8uccdL79
Counter: 2
Worker used: "12D3KooWKPcNwR6EMq3sqm4sKtUKmZbMhPQ2dk1zr8YNgjdu9Xqn"
Call will be to : https://frequent-sleek-river.ethereum-goerli.discover.quiknode.pro/<your api key>/

Success! Go ahead and replace the round-robin mode with the random mode in your config file, stop and start the gateway and have a look at the different endpoint management.

Congrat's, you just took a major step toward keeping you dAPP decentralized, available and performant! Now it's time to dive into the Fluence protocol and technology stack to learn how to improve upon the basic substrate and compete for hackathon bounties.

Developing With Fluence

Fluence's decentralized serverless protocol and solution stack allows developers to quickly create decentralized applications and protocols by distributing services for subsequent execution to peers of the open and permissionless Fluence peer-to-peer compute network. Specifically, developers:

• express their business logic in Rust code compiled to wasm32-wasi
• create a Deal, i.e., a construct that links on-chain contract economics and off-chain resources necessary for peers to run a service, which entails escrowing stablecoin, currently limited to (testnet) USDC, to the Deal contract
• deploy their Wasm modules plus linking instructions as a uniquely addressable service to p2p network storage, i.e., IPFS

With a Deal in place, resource owners, i.e., owner/operators of one or more peer, make a decision whether to host the service and if so, participate in the Deal by providing a stake to the Deal contract and pulling the corresponding service assets required for hosting from IPFS. As a matter of fact, peers utilize Workers, omitted from Figure 2 for simplicity reasons, to implement their side of a Deal. See Figure 2.

sequenceDiagram
    title: Figure 2: Stylized Deal Creation For Service Deployment

    actor D as Developer
    participant CF as Contract factory
    participant C as Contract
    participant N as Network storage (IPFS)
    actor R as Resource owner
    participant P as Peer i owned by resource owner

    D ->> D: Business logic to Rust To Wasm
    D ->> CF: request deal contract for service
    CF ->> C: generate Deal contract  for service
    par
        D ->> C: escrow funds
        D ->> N: upload service package
    end
    R ->> CF: listen for new contracts
      loop listen to on-chain events
        alt new contract
        R ->> C: evaluate deal
        alt like deal
          R ->> C: join deal with stake
          P ->> N: request service package
          P ->> P: host service
          P ->> P: wait for service request
          alt get request
            R ->> C: claim payment
          end
        end
      end
    end

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While this sounds, and is, elaborate, Fluence CLI, see below, takes care of most of the scaffolding and workflow management for you.

Note: At this point, the marketplace for Fluence's decentralized serverless isn't quite finished. The supply side has not been enabled and on the demand side, parameters are fixed for the testnet. That is, developers are not able to provide custom Deal parameters, such as willingness to pay for service execution. Instead, these parameters, i.e. price of execution per epoch and epoch duration, are hard-coded and used by Fluence CLI to create the corresponding Deal contract and transaction for you to sign. Moreover, economics are limited to the testnet using testnet tokens and throughout the EthDenver hackathon, resource owners may not claim their periodic share of revenue from the Deal's escrow.

Setting Up For Developing With Fluence

To get going, you need to install and setup a few dependencies.

Note: Fluence tooling works on most *nix systems including OSX and Windows Linux Subsystem. At this time, Windows is not supported.

Off-chain Dependencies

• node 18 LTS
• Fluence CLI
• Rust (optional; Fluence CLI will install if not already in your environment)
• For VSCode, there is a helpful Aqua language support package available

Note that Fluence CLI installs missing dependencies as needed ("lazy install"). If you want all your dependencies installed at once, use the fluence dependencies i command.

On-chain Dependencies

• Wallectconnect compatible wallet, e.g., MetaMask, setup for and funded with:
  • Aurora testnet parameters
  • Aurora faucet
  • Fluence USDC testnet faucet

You will need Aurora (testnet) ETH and Fluence (testnet) USDC. This is as good a time as any to head over to those faucets and get your allocations. As an experienced Web3 dev, you know it's god hygiene to set up a new account, say, fRPC-dev, for the Aurora testnet and testnet tokens.

RPC Endpoints

Since fRPC works with existing centralized or self-hosted RPC providers, you want at least three provider urls with appended API keys to the chain of your choice. Multi-chain support is currently not supported by fRPC Substrate (hint, hint to all you hackathoners). For Ethereum's Goerli testnet, for example:

• Infura: https://goerli.infura.io/v3/
• Alchemy: https://eth-goerli.g.alchemy.com/v2/
• QuickNode: https://frequent-sleek-river.ethereum-goerli.discover.quiknode.pro//

Each of the listed providers has a free account option and supports the API key in the url style, rather than the header, which is the current gateway implementation choice; a choice you should feel free to override and customize to your needs.

Tools And Tooling

The most prominent developer's helper is Fluence CLI, which allows you to manage the entire lifecycle of a project including Rust and Aqua code as well as Deals. From scaffolding your project, services and modules to deal creation and service deployment, Fluence CLI has you covered. Moreover, Fluence CLI can scaffold JS projects using js-client allowing you to create, or integrate, Fluence projects for the browser or node app. See Figure 3 for a quick overview of workflows managed by Fluence CLI and the associated commands. If you have Fluence CLI installed, use fluence --help to get a more complete overview of topics and commands.

Figure 3: Stylized Project Creation And Deployment Workflow With Fluence CLI

    stateDiagram
    
    [*] --> InitProject: fluence init
    InitProject --> CreateNewService: fluence service new
    InitProject --> AddExistingService: fluence service add
    CreateNewService --> Service
    AddExistingService --> Service
    Service --> AddNewModules: fluence module new
    Service --> AddExistingModules: fluence module add
    Service --> LocalTesting: fluence service repl, cargo test
    Service --> DeployedService: fluence deal deploy
    DeployedService --> RunService: fluence run

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Fluence CLI uses multiple yaml config files. Below find references to the most important one populated with parameters from our fRPC-Substrate project. You can find the schemas in the schemas directory. Note that Fluence CLI creates config files lazily, i.e., as needed.

fluence.yaml -- the root project config file that manages version, dependencies, and more:

version: 2
aquaInputPath: src/aqua/main.aqua             # path where to look for default aqua files, you can change that
workers:                                      # worker settings for deploy
  defaultWorker:
    services: [ eth_rpc ]
deals:                                        # deal settings for deploy
  defaultWorker:
    minWorkers: 1                             # default min worker settings -- you want your service deployed ot at least 1 worker
    targetWorkers: 3                          # default max worker settings -- you want your service deployed ot at least 3 workers 
hosts:
  defaultWorker:
    peerIds:
      - 12D3KooWJ4bTHirdTFNZpCS72TAzwtdmavTBkkEXtzo6wHL25CtE

relays: stage                                 # Name of Fluence network used
services: 
  eth_rpc:                                    # service name
    get: wasm-modules/                        # and where to get the service config

service.yaml -- the service config file that manages module dependencies

You find this in the service directory root, i.e., wasm-modules in our case.

version: 0
name: eth_rpc                 # name of the service which is referenced in fluence.yaml
modules:                      # modules included
  facade:                     # service API module, see https://fluence.dev/docs/marine-book/marine-runtime/module-types/ for more info
    get: eth-rpc
  curl-adapter:               # other modules
    get: curl-adapter

module.yaml -- the module config file

Each module includes a module.yaml file in its root, e.g., eth_rpc and curl-adapter.

# curl-adapter/module.yaml
version: 0
type: rust                    # language used to code the module
name: curl_adapter                      
mountedBinaries:              # effector module specific: what mechanism is used to access host resources
  curl: /usr/bin/curl         # host path to binary mapped to the alias used in the module's FFI link section

The minimum key for a module file are: version, type and name. Effector modules, however, may need additional information such as MountedBinaries. Such information needs to be manually added.

project-secrets.yaml, user-secrets.yaml -- the cryptographic key file

Fluence uses cryptographic keys in a variety of contexts including end-to-end encryption, client peer id determination and securing services. By default, Fluence CLI creates a keypair in user-secrets.yaml, which is placed in the global .fluence directory in your home directory.

# user-secrets.yaml
version: 0
keyPairs:
  - peerId: 12D3KooWS8G1SdmBe...6SU2Ay3nZMqezpW3tGqoBXwozDnT
    secretKey: z0DrDzCaqRHI1T...mh7MHav1v2Q2daJogfOUBFMc=
    publicKey: CAESIPJQetYHX4...VdCwTqXvfGBa+kiIUK5Ee9bh6u8oE
    name: auto-generated
defaultKeyPairName: auto-generated

The default keys are available and used by all your projects unless you create a project-specific key pair with the fluence key command and saved in the project-secrets.yaml file in the project-local .fluence directory. Since we are in defualt mode for our current setup, projects-secrets.yaml is not populated.

# projects-secrets.yaml
version: 0
keyPairs: []

workers.yaml

This file, also located in the project .fluence directory, holds all the deployment information necessary to track your distributed resources both on- and off-chain.

version: 0
deals:
  defaultWorker:
    definition: Qmcvoi6tZeBEkva2yn7cXJd8GiocKmkuzuz8L9VtfNdSG2,       # CID
    timestamp: 2023-04-09T06:21:36.559Z,
    dealIdOriginal: "0x0CC9E494CaFDea602b09013a8743012Ce720def2",     #  Original deal id 
    dealId: 0cc9e494cafdea602b09013a8743012ce720def2,                 # current deal id which may change after deal update 
    chainNetwork: testnet,                                            # Fluence on-chain network alias
    chainNetworkId: 80001                                             # Fluence on-chain chain id 

See FLuence CLI for more details. For implementing your business logic with Rust and compiling it to wasm32-wasi, aka Wasm, module(s), see the Marine book. To learn more about distributed choreography and composition of services, see the Aqua book.

Hacking On fRPC Substrate

Fluence's fRPC Substrate is a starter kit that includes all the components you need to quickly enable your dAPP with decentralized RPC using existing centralized RPC providers, e.g., Infura, Alchemy, QuickNode, etc., without touching your existing frontend Web3 code. fRPC substrate consists of the following code components, see Figure 4:

• RPC API "adapter" code written in Rust and compiled to wasm32-wasi modules that are deployable to any peer in the Fluence p2p network
• Aqua code for distributed algorithms, such as Random and Round Robin selection, using the distributed Wasm connectors for request-response handling over libp2p
• A gateway app server that bridges libp2p transport to the HTTP transport expected by your dAPPs' Web3 SDK, such as web3js, ethers, etc. Note that the expectation at this point is for you to self-host the gateway at a location of your choosing.

Figure 4: Stylized fRPC Use With dAPPs

    sequenceDiagram
    
    participant D as dApp
    participant G as Gateway
    participant N as Fluence p2p network
    participant R as Centralized RPC providers
    
    G ->> G: Configure and start Gateway
    D ->> D: Use gateway Address:port in web3 sdk setup
    D ->> G: Make Web3 request
    G ->> N: Call one or more Fluence services
    N ->> R: Call one or more different RPC providers
    R ->> N: Services processes response based on specified algo
    N ->> G: Gateway receives "curated" response
    G ->> D: dApp receives response
    D ->> D: dApp does its thing

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In order to use the fRPC substrate out-of-the-box or after customization, you need to:

• have three or more centralized RPC endpoints ready, where each provider url needs to contain the API key, e.g.,
• deploy a deal
• deploy the service
• update the gateway configuration
• run the gateway
• use the gateway url in your web3 sdk's HTTP transport config

fRPC Wasm Components

fRPC Substrate comes with one service comprised of two Wasm modules, which you can find in the wasm-modules directory. The service is called 'eth_rpc' and the included modules are a curl_adapater and eth_rpc. The curl_adapter module is a generic, re-usable module allowing access a peer's curl binary, if permissioned by the peer, and exposes the curl_request function. Any modules requiring curl access may use the curl_adapter modules via FFI linking with the curl_request function.

The eth_rpc module manages the json-rpc requests and responses initiated and consumed by Aqua scripts as he result of some frontend event, .e.g. our dAPP or curl request. Once available on peers of the Fluence p2p network, the eth-rpc services, aka RPC endpoint adapter, allows us to call one or more RPC endpoints using Aqua for choreography and composition of services.

Before you can deploy your service, use fluence build in the root dir to compile each module's Rust code to wasm32-wasi output:

fluence build
# Making sure all services are downloaded...
# Making sure all services are built...
    Finished release [optimized] target(s) in 0.61s

See target dir for curl_adapter.wasm and eth_erpc.wasm, respectively. With the wasm modules available, you can locally interact with them using Marine REPL:

fluence service repl

fluence service repl
? Enter service name from fluence.yaml, path to a service or url to .tar.gz archive wasm-modules
# Making sure service and modules are downloaded and built...
    Finished release [optimized] target(s) in 0.18s

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Execute help inside repl to see available commands.
Current service <module_name> is: eth_rpc
Call eth_rpc service functions in repl like this:

call eth_rpc <function_name> [<arg1>, <arg2>]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Welcome to the Marine REPL (version 0.19.1)
Minimal supported versions
  sdk: 0.6.0
  interface-types: 0.20.0

app service was created with service id = f0fc66d9-1fc6-494f-bcc1-104970875730
elapsed time 254.67135ms

1> i
Loaded modules interface:
exported data types (combined from all modules):
data MountedBinaryResult:
  ret_code: i32
  error: string
  stdout: []u8
  stderr: []u8
data U64Value:
  value: u64
  success: bool
  error: string
data BytesValue:
  value: []u8
  success: bool
  error: string
data JsonString:
  value: string
  success: bool
  error: string

exported functions:
curl_adapter:
  func curl_request(cmd: []string) -> MountedBinaryResult
eth_rpc:
  func block_number(uri: string) -> U64Value
  func call_get_accounts(uri: string) -> [][]u8
  func accounts(uri: string) -> []JsonString
  func call(uri: string, req: string, block: u64) -> BytesValue
  func eth_call(uri: string, method: string, json_args: []string) -> JsonString

2>call eth_rpc eth_call ["https://<your network>.infura.io/v3/<your api key>", "eth_blockNumber", []]
result: {
  "error": "",
  "success": true,
  "value": "\"0x82a08d\""
}
 elapsed time: 588.092888ms

3>

The i command lists all the exported interfaces from the wasm modules in Aqua instead of Rust notation. In expoerted functions you seee the module namespace, e.g., curl_adapter , and exported functions, e.g., curl_request. To execute a function, use call <namespace> <function name> [<parameters>].

Adding Modules To A Service

Regardless of your customization requirements, you probably will have no reason to modify the curl_adapter and eth_rpc modules. However, you may want to add new modules, or even services, to handle your additional business logic requirements. For example, you may want to capture RPC endpoint performance data, such as response times and availability, to some Web3 storage, e.g., IPFS or Ceramic, for further analysis to, say, derive a weighting scheme for endpoint selection.

Fluence CLI allows you to quickly crate a new, or add an existing, module to your project. For example,

 fluence module new
? Enter module path wasm-modules/demo-module
Successfully generated template for new module at wasm-modules/demo-module

Which created a Rust project in the wasm-module/demo-module directory ready for you to customize. When you're done, you add the new module to your service config, service.yaml:

fluence module add
? Enter path to a module or url to .tar.gz archive wasm-modules/demo
? Enter service name from fluence.yaml or path to the service directory wasm-modules
Added demo to ~/localdev/fRPC-Substrate/wasm-modules/service.yaml

The demo module is now part of the service and fluence build, for example, now compiles the demo module as part of the project build. You can create a new service with the fluence service new command. Note that the implication of creating a new service, possibly in a new project directory, is that you intend to deploy that service separately from the eth-rpc service. Of course, you will need to write Aqua code to be able to interact with your new module.

To get rid of the demo project for now, use fluence module remove to unlink the module from the fluence.yaml and service.yaml files; the old rm -r <path/demo> gets rid of the code template.

Deploying A Service

With a service, in this case the eth-rpc service, ready for deployment, we simply use the fluence deal deploy command:

fluence deal deploy
Connecting to: /dns4/stage.fluence.dev/tcp/19004/wss/p2p/12D3KooWJ4bTHirdTFNZpCS72TAzwtdmavTBkkEXtzo6wHL25CtE

# 1 if Deal is already in place update or create new Deal?
? Do you want to redeploy worker defaultWorker Yes
    Finished release [optimized] target(s) in 0.22s

# 2 upload packaged assets
ipfs: did pin QmTvNwBeDop1yD9dLNjgrzfBMsgtrBmD859ahqQS1EWhbj to /dns4/ipfs.fluence.dev/tcp/5001
<...>
ipfs: file bafkreichjd77xy3bz4whsuyo2rmtgtwfjh4mqcwlzb74mvpgn5xfrjm72a pinned to /dns4/ipfs.fluence.dev/tcp/5001

# 3 process upload responses for local updates in workers.yaml
Updating deal for worker defaultWorker

# 4 request signing of escrow payment transaction

# Connecting to wallet......
To approve transactions to your wallet using metamask, open the following url:

https://cli-connector.fluence.dev/?wc=d5494d58588812c1ca148268c5a236daa127092d1a8a7a1db50c2ffdb1aa40be%402&relay-protocol=irn&symKey=d1a4b5954b6e46c1fd70174f0de7a5a78b14346d9d59963baf003d41c90e1284

or go to https://cli-connector.fluence.dev and enter the following connection string there:

wc:d5494d58588812c1ca148268c5a236daa127092d1a8a7a1db50c2ffdb1aa40be@2?relay-protocol=irn&symKey=d1a4b5954b6e46c1fd70174f0de7a5a78b14346d9d59963baf003d41c90e1284

Confirm transaction in your wallet...
# Waiting for transaction to be mined......

# 5 if escrow payment is processed, deal deployment is finalized
Success!

Success!

created deals:
  defaultWorker:
    deal: https://explorer.testnet.aurora.dev/address/0x258223B18962d804Fca4784245c3a5e0E3Bd8548
    worker definition: bafkreichjd77xy3bz4whsuyo2rmtgtwfjh4mqcwlzb74mvpgn5xfrjm72a

One little command is doing quite a bit so you don't have to. Let's work through the process:

• once we launch fluence deal deploy we create a (new) Deal with both on-chain and off-chain activities
• for an up-to-date look, all service assets, i.e., modules, are (re-) compiled (1)
• the wasm modules and config are uploaded to IPFS node where deal-participating peer's workers can fetch the package by CID (2)
• get back CID and update local file(s) (3)
• if a deal is already in place, which was so you could run the Quickstart demo quickly, either update the existing deal or create a new one: create a new one! (4)
• now you have to get involved! you are presented with the uri to get metamask to ask you to sign your escrow payment to the contract (5). Copy and paste the uri to your browser and eventually, Metamask should pop-up with a signing request. The transaction displays only in hex, so double check the other request params to make sure you're signing the Aurora testnet transaction. This is what you should see:
• once you signed the transaction and the contract was successfully updated, we are done (6) !

Fluence CLI did a bunch of work for us behind the scenes and signing the transaction is a lot quicker than entering (virtual) credit card information. The parametric details necessary to write Aqua scripts are save in deals.aqua and serves as an important dependency in your Aqua scripts, as we'll see in the next section.

Note that the deal's section in fluence.yaml specifies the number of workers that should be deployed specified by targetWorkers. The default is three (3) and can be customized. It is important to note that this is a desire not a guarantee as the actual deployment depends on the number of peers willing to participate in the deal. Currently, all the testnet peers operate by Fluence will participate in your deal.

fRPC Algorithms

Now that we got our services deployed and ready for action, it's time to look at Aqua, which is utilized by the Gateway to bridge HTTP to/fro libp2p. The fRPC substrate comes with basic implementations of several algorithms useful in mitigating failure as the result of availability and lack of trustlessness with respect to RPC endpoints and possibly peers. Before we dive into the algorithms, let's have a look at the Aqua code and structure.

rpc.aqua contains the necessary dependencies and algorithms.

-- rpc.aqua
import "@fluencelabs/aqua-lib/builtin.aqua"
import "deals.aqua"
import "services.aqua"
import "@fluencelabs/registry/subnetwork.aqua"
import Registry, Record from "@fluencelabs/registry/registry-service.aqua"
import "@fluencelabs/spell/spell_service.aqua"

Two of the dependencies (should) stand out: deals.aqua and services.aqua as they are local files located in the project .fluence directory: services.aqua contains the interface exports from the eth-rpc wasm module and deals.aqua maps the values from deployed.yaml to data structures usable by your aqua code. Since these files are dynamically generated by Fluence CLI, you need to (re-) compile your Aqua after every change to your Wasm code or deal deploy updates. For all things Aqua refer to the Aqua book, the aqua playground and the respective repos: aqua-lib, registry, spell.

Random

Use: Set mode to "random" in your gateway config file

Randomization the selection of one out of many RPC endpoints by itself is a weak algorithm to mitigate single point of failure or byzantine behavior. However, it can be an important building block for more effective algorithms such as failover and quorum/consensus from both RPC providers and network peers.

The fRPC substrate implementation is very basic from a business logic perspective but illustrates how to randomly choose both a worker, which represents the deployed service on a particular peer, and an RPC endpoint:

func randomLoadBalancing(uris: []string, method: string, jsonArgs: []string, callFunc: string, string, []string -> JsonString) -> JsonString:
  on HOST_PEER_ID:                                                                  --< 1
    workers <- getWorkers()                                                         --< 2
    workersNum = workers.length
    -- choose worker randomly
    timeW <- NumOp.identity(Peer.timestamp_sec())
    workerNumber = timeW % workers.length                                           --< 3
    worker = workers[workerNumber] 
    -- choose provider randomly
    timeP <- NumOp.identity(Peer.timestamp_sec())
    providerNumber = timeP % uris.length                                            --< 5
    provider = uris[providerNumber]
    result <- callOnWorker(worker, provider, method, jsonArgs, callFunc)            --< 6
  Logger.logWorker(worker)                                                          --< 7
  Logger.logCall(uris[providerNumber])
  <- result

We want to execute our Aqua program on the peer the client, i.e. the gateway's client peer, connected to (1). To setup for our randomized worker and endpoint selection, we need to get the workers running our eth-rpc service (2). We then calculate the index workerNumber as a random integer (3) and do the same for the endpoint provider (5). Finally, we call the chosen worker with the chosen endpoint url (6) and print our randomly chosen integers to the screen (7) before returning the result.

Round robin

Use: Set mode to "round-robin" in your gateway config file

func roundRobin(uris: []string, method: string, jsonArgs: []string, counterServiceId: string, counterPeerId: string, callFunc: string, string, []string -> JsonString) -> JsonString:
  on counterPeerId:                                                           --< 1
    Counter counterServiceId
    requestNumber <- Counter.incrementAndReturn()
  on HOST_PEER_ID:                                                            --< 2
    workers <- getWorkers()
    workerNumber = requestNumber % workers.length
    worker = workers[workerNumber]                                            --< 3
    providerNumber = requestNumber % uris.length
    provider = uris[providerNumber]                                           --< 4
    result <- callOnWorker(worker, provider, method, jsonArgs, callFunc)      --< 5
  Logger.logWorker(worker)
  Logger.logCall(uris[providerNumber])
  <- result

A round robin algorithm cycles through the different options usually in a predictable manner. This substrate implementation is no different. In order to keep state of the cycle index, we use a counter based on a local, js-client based service implementation (1). Here, the peer executing the Counter service is the (local) client-per implemented by the gateway. Note that the state of the counter is limited to the life of the gateway. With the incremented counter in place, we had to our relay (2), determine our worker (3) and provider (4) indexes, call for the service execution (5), log and return the result.

Quorum

Use: Set mode to "quorum" in your gateway config file

func quorum(
  uris: []string, quorumNumber: u32, timeout: u32, method: string, jsonArgs: []string, quorumServiceId: string, quorumPeerId: string,
  callFunc: string, string, []string -> JsonString
) -> QuorumResult:
  results: *JsonString
  on HOST_PEER_ID:
    workers <- getWorkers()
    for worker <- workers par:                                        --< 1
      on worker.metadata.peer_id via worker.metadata.relay_id:
        -- choose provider randomly
        timeP <- NumOp.identity(Peer.timestamp_ms())
        providerNumber = timeP % uris.length
        provider = uris[providerNumber]
        results <- callFunc(provider, method, jsonArgs)               --< 2
    -- wait all results from all workers with timeout
    join results[workers.length - 1]
    par Peer.timeout(timeout, "")                                     --< 3
  on quorumPeerId via HOST_PEER_ID:
    Counter quorumServiceId
    -- check all results that we got
    quorumResult <- QuorumChecker.check(results, quorumNumber)        --< 4
  <- quorumResult

A quorum, aka "off-chain consensus", "determines" a result by a ranked frequency distribution of the result pool and makes a selection against a quorum threshold value, e.g., 2/3 of items in the results pool must be equal for a quorum result to accepted. Moreover, additional parameters such as minimum number of items in the result pool may be added. depending on you trust of the peers processing the endpoint requests or even the peer executing the quorum algorithm, additional verification steps may have to be added. There is one more pertinent consideration when it comes to designing quorum algorithms: the differentiation betwen (on-chain) read and write operations.

In the fRPC substrate implementation, we provide a basic quorum algo that polls each endpoint in parallel (1) and captures the results in a stream variable (2) and bound the loop with a timeout condition running (3) in parallel to (1). See the Aqua book for more details. Finally, we check the results and return the result (4). As evidenced by the code, no considerations to differentiate between rad and write operations is made, wich might prove disadvantageous when submitting, for example, a signed transaction (hint, hint to all you hackathon participants).

Summary

fRPC is a design pattern to efficiently mitigate risks inherent in centralized RPC providers for dApps using Fluence's decentralized serverless compute protocol. fRPC Substrate is a basic implementation of the fRPC design pattern that dApp users can use put of the box with no changes to their frontend. Moreover, Fluence is sponsoring hackathons, like EthDenver 2023, for developers to try the substrate and hack on and expand on the control algorithms provided to serve their needs and provide improvements to the community.

For support, to discuss your ideas or to schedule presenntations of your solutions to the Fluence and fRPC community at large, reach out in discord or telegram.

Happy Hacking!

Contribution

Found a mistake, inaccuracy or have other improvement suggestions? Open an issue or a pull request! Note that contributions submitted will be licensed according to the terms of LICENSE.