Fluence provides an open Web3 protocol, framework and associated tooling to develop and host applications, interfaces and backends on permissionless peer-to-peer networks. An integral part of the Fluence solution is the Aquamarine stack comprised of Aqua and Marine. Aqua is a new programming language and paradigm purpose-built to program distributed networks and compose applications from distributed services. Marine is a general purpose Wasm runtime and toolkit, allows developers to build distributed services that can be composed into distributed applications by Aqua.
Price (feed) oracles are probably the most used and in-demand oracle type and tend to have a significant impact on the success and profitability of DeFi and related on- and off-chain operations. In this example, we demonstrate how to create a decentralized, off-chain price (feed) oracle on the Fluence peer-to-peer network from a set of distributed, re-usable Marine services composed by Aqua.
Figure 1: Stylized Price Oracle Network And Service Process
As outlined in Figure 1, we use one or more services distributed across the Fluence peer-to-peer network to obtain price quotes from sources. For example, we could have one service capable of querying one or more sources such as DEX contracts deployed on multiple network peers allowing us to poll price sources in parallel. We then join these results and submit them to a processing service also deployed on the peer-to-peer network to establish, for example, an oracle point-estimate. Once we've obtained our oracle, we return it to the peer-client, e.g., a browser.
opens a browser tab allowing you to enter the coin name and currency to price it in. In return, you get the oracle from the processed individual price quotes.
Figure 3: Browser Peer Client For Price Oracle Application
Please note that the coin name must the full name, e.g., ethereum or bitcoin instead of eth or btc, whereas currency is specified in the traditional ISO 4217 Alpha-3 codes.
**Prerequisites:** If you want to follow along, compile Wasm modules, create services and deploy service, you need Rust, Node and a few Fluence tools installed. Please see follow the [Setup](https://doc.fluence.dev/docs/tutorials_tutorials/recipes_setting_up) instructions.
Applications are composed from one or more services available on one or more Fluence peer-to-peer nodes. Services are comprised of one or more Wasm modules providing a wide range of compute functionality and access to persistance, e.g. IPFS and SQLite. For the purpose of our objective, we need a service that can call on some API to source price quotes. In an ideal, production world, this would be calling on a large set of DEX contacts to obtain price pairs and, say, lquidity, over a particular window of time. For our purposes, we simplify the process and call on the [Coingecko API](https://www.coingecko.com/api/documentations/v3) and add a random jitter to each quote retrieved to give us some variance.
For implementation details, see [price_getter_service]("./../price_getter_service/src/main.rs), which compiles to our desired wasm32-wasi target. Since Wasm modules don't have sockets but we need to use cUrl, which is provided by the host node. In order to do that, we fist need to write an adapter that allows us to access the cUrl service from a Wasm module and then link that service to our price_getter service. See [cUrl adapter example](./marine-scripts/curl_adapter) for more details on the implementation of our [curl adapter service](./curl_adapter/src/main.rs).
Figure 2: Stylized Service Creation By Marine Module Linking
As see in Figure 2, we link the price_getter module and curl adapter module into a price_getter service ready for deployment to the Fluence peer-to-peer network. Before we proceed, we have one more service to consider: the price quote processing service which yields the oracle. Again, we simplified what could be an extensive processing algorithm into a simple mean calculation, see [mean_service]("./../mean_service/src/main.rs") for implementation details. Unlike the price getter service, mean service is a simple, FaaS compute module that deploys on any number of network peers.
We now have our code in place and area ready to compile and our compilation instructions are contain in the `scripts/build.sh` script, which basically instructs the the code is compiled with `marine` and that the resulting Wasm modules are copied to the `artifacts` directory. In the project directory:
```text
./scripts/build.sh
```
which gives you the updated Wasm modules in the `artifacts` directory.
The next step is to deploy the two services to one or more peers and we use the `fldist` tool to get this done. First, we need to now what peers are available and we can get an enumeration from:
```text
fldist env
```
*Please note that multiple service instances have been already deployed and the (peer id, service id) tuples can be found in [data]("./data/deployed_services.json) json file. While your more than welcome to deploy your services, you don't have to in order to use them.*
Pick any of the peer ids from the listed peers to deploy your services. Let's say we use peer id `12D3KooWFEwNWcHqi9rtsmDhsYcDbRUCDXH84RC4FW6UfsFWaoHi`:
to deploy a mean service. Please take note of the service-id you get back for each fo the deployments, which are needed to locate the service in the future. For example
