registry/README.md

# Registry

- [Registry](#registry)
  - [Overview](#overview)
  - [Why is it important?](#why-is-it-important)
  - [What is it?](#what-is-it)
  - [How to Use it in Aqua](#how-to-use-it-in-aqua)
    - [How to import](#how-to-import)
    - [How to create Resource](#how-to-create-resource)
    - [How to register Provider](#how-to-register-provider)
    - [How to register Node Provider](#how-to-register-node-provider)
    - [How to delete Node Provider](#how-to-delete-node-provider)
    - [How to resolve Providers](#how-to-resolve-providers)
    - [How to execute a callback on Providers](#how-to-execute-a-callback-on-providers)
    - [Notes](#notes)
  - [Use cases](#use-cases)
    - [Services discovery](#services-discovery)
    - [Service high-availability](#service-high-availability)
    - [Subnetwork discovery](#subnetwork-discovery)
    - [Load balancer](#load-balancer)
  - [API](#api)
  - [References](#references)
    - [Learn Aqua](#learn-aqua)

## Overview

There are many [services](https://doc.fluence.dev/docs/concepts#services) in the network on different peers and should be a way to find and resolve them in runtime without prior knowledge about exact service providers. This approach gives robustness and flexibility to our solutions in terms of discovery, redundancy and high availability.

In centralized systems, we can have centralized storage and routing, but in p2p decentralized environments, this problem becomes more challenging. Registry is our view on the solution for this problem.
![image](images/registry.png)

## Why is it important?

Scalability, redundancy and high availability are essential parts of a decentralized system, but they are not available out of the box. To enable these, information about services should be bound with peers providing them. Also, these networks are frequently changing and should be reflected and resolvable in runtime to provide unstoppable access. So you should have some decentralized protocol to update and resolve information about routing, both global and local.

## What is it?

Registry is available (built-in) on every Fluence node. It provides service advertisement and discovery. This component creates relationships between unique identifiers and groups of services on various peers. So service providers can join or disconnect during runtime and be discoverable in the network.

However, Registry is not a plain KV-storage. Instead, it is a composition of the Registry service for each network participant and the scheduled scripts maintaining replication and garbage collection.

If you want to discover a group of services on different peers without prior knowledge in runtime, you should register a **Resource**. A resource is a group of services or peers united by some common feature. Please notice that resource lifetime is ~24 hours. However, if the resource has been accessed recently, it will not be garbage-collected for the next 24 hours from the last access.

A combination of `service_id` and `peer_id` represents a service **Provider**.

![image](images/discovery.png)
![image](images/mapping.png)

There are two types of providers depending on a peer this service operates on. **Node Providers** correspond to a full-featured Rust [node](https://doc.fluence.dev/docs/node) and the rest of **Providers** — to a [JS peer/client](https://doc.fluence.dev/docs/fluence-js). And a record for any provider should be renewed every 24 hours to avoid garbage collection.

As for now, every resource is limited by [number](./service/src/defaults.rs#25) of providers `32` it can hold, disregarding records for the node services. So local services have no limitation for registration in the local registry. Other providers' records are ranked by peer weights in the local [TrustGraph](https://github.com/fluencelabs/trust-graph/blob/master/README.md#what-is-it) instance. So locally every node has a list of the most trusted service providers. "Trusted" means that in terms of TrustGraph, a service provider complies with requirements defined by node owner.

There is no permissions management at the moment, but in the coming updates, a resource owner will provide a challenge to check against.

## How to Use it in Aqua

### How to import
```rust
import "@fluencelabs/registry/resources-api.aqua"
import "@fluencelabs/registry/registry-service.aqua"

func my_function(resource_id: string) ->  []Record, *Error:
   result, error <- resolveProviders(resource_id)
   <- result, error
```

### How to create Resource
- `createResource(label: string) -> ?ResourceId, *Error`
- `createResourceAndRegisterProvider(label: string, value: string, service_id: ?string) -> ?ResourceId, *Error`
- `createResourceAndRegisterNodeProvider(provider_node_id: PeerId, label: string, value: string, service_id: ?string) -> ?ResourceId, *Error`

Let's register a resource with the label `sample` by `INIT_PEER_ID`:
```rust
func my_resource() -> ?ResourceId, *Error:
   id, error <- createResource("sample")
   <- id, error
```

- `createResourceAndRegisterProvider` and `createResourceAndRegisterNodeProvider` are the combination of resource creation and provider registration
- `label` is a unique string for this peer id
- creation is successful if the resource id returned
- `*Error` accumulates errors from all affected peers
### How to register Provider
- `registerProvider(resource_id: ResourceId, value: string, service_id: ?string) -> bool, *Error`
- `createResourceAndRegisterProvider(label: string, value: string, service_id: ?string) -> ?ResourceId, *Error`


Let's register local service `greeting` and pass some random string like `hi` as a value:
```rust
func register_local_service(resource_id: string) -> ?bool, *Error:
   success, error <- registerProvider(resource_id, "hi", ?[greeting])
   <- success, error
```

- `value` is a user-defined string that can be used at the discretion of the user
- to update the provider record, you should register it one more time to create a record with a newer timestamp
- to remove the provider you should stop updating it
- you should renew the record every 24 hours to keep the provider available

### How to register Node Provider
- `registerNodeProvider(provider_node_id: PeerId, resource_id: ResourceId, value: string, service_id: ?string) -> bool, *Error`
- `createResourceAndRegisterNodeProvider(provider_node_id: PeerId, label: string, value: string, service_id: ?string) -> ?ResourceId, *Error`

Let's register service `echo` hosted on `peer_id` and pass some random string like `sample` as a value:
```rust
func register_external_service(resource_id: string, peer_id: string) -> ?bool, *Error:
   success, error <- registerNodeProvider(peer_id, resource_id, "hi", ?[greeting])
   <- success, error
```

- the record will not be garbage-collected from the provider's node, but it is better to update it every 24 hours. In the following updates renewing process will be handled by the node with scheduled scripts

### How to delete Node Provider
- `removeNodeFromProviders(provider_node_id: PeerId, resource_id: ResourceId)`
Let's remove node provider's record from target node:
```rust
func stop_provide_external_service(resource_id: string, peer_id: string):
   removeNodeFromProviders(peer_id, resource_id)
```

- it will be removed from the target node and in 24 hours from the network
### How to resolve Providers
- `resolveProviders(resource_id: ResourceId, ack: i16) -> []Record, *Error`

Let's resolve all providers of our resource_id:
```rust
func get_my_providers(resource_id: string, consistency_level: i16) -> []Record, *Error:
   providers, error <- resolveProviders(resource_id, consistency_level)
   <- providers, error
```

- `ack` is a characteristic that represents min number of peers who asked for known providers

### How to execute a callback on Providers
- `executeOnProviders(resource_id: ResourceId, ack: i16, call: Record -> ()) -> *Error`


```rust
func call_provider(p: Record):
   -- topological move to a provider via relay
   on p.peer_id via p.relay_id:
       -- resolve and call your service on a provider
       ...
       Op.noop()

-- call on every provider
func call_everyone(resource_id: String, ack: i16):
   executeOnProviders(resource_id, ack, call_provider)
```

- it is just a combination of `resolveProviders` and `for` loop through records with callback execution
- it can be useful in case of broadcasting events on providers
- look in the [docs](https://doc.fluence.dev/aqua-book/libraries/registry#call-a-function-on-resource-providers) for more detailed example
### Notes
You can redefine [`REPLICATION_FACTOR`](https://github.com/fluencelabs/registry/blob/main/aqua/resources-api.aqua#L10) and [`CONSISTENCY_LEVEL`](https://github.com/fluencelabs/registry/blob/main/aqua/resources-api.aqua#L11).


## Use cases
### Services discovery
Discover services without prior knowledge about exact peers and service identifiers.

### Service high-availability
Service provided by several peers still will be available for the client in case of disconnections and other providers' failures.

![image](images/availability.png)

### Subnetwork discovery
You can register a group of peers for a resource (without specifying exact services). So you "tagging" and group the nodes to create a subnetwork.

![image](images/subnetwork.png)

### Load balancer
If you have a list of service providers updated in runtime, you can create a load-balancing service based on your preferred metrics.

## API

API is defined in the [resources-api.aqua](./aqua/resources-api.aqua) module. API Reference will soon be available in the documentation.


## References
- See [Registry documentation](https://fluence.dev/aqua-book/libraries/registry).

### Learn Aqua

* [Aqua Book](https://fluence.dev/aqua-book/)
* [Aqua Playground](https://github.com/fluencelabs/aqua-playground)
* [Aqua repo](https://github.com/fluencelabs/aqua)