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docs: lint fixes
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Signed-off-by: Pradeep Mishra <pradeepbbl@gmail.com>
Signed-off-by: Pradeep <pradeepbbl@gmail.com>
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pradeepbbl committed Sep 25, 2024
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Expand Up @@ -24,28 +24,6 @@ For such cases the gRPC core libraries support few alternative resolver* also ex
* [Java Client](https://grpc.github.io/grpc-java/javadoc/io/grpc/ManagedChannelBuilder.html#forTarget(java.lang.String))
* [Golang](https://pkg.go.dev/google.golang.org/grpc#NewClient)

A sample workflow of a deployment with proxy sidecar using `in-process` mode (for `rpc` the process is same)

```mermaid
sequenceDiagram
participant flagd-sync.service
participant proxy-sidecar-agent
participant flagd-provider
participant application
flagd-provider-->proxy-sidecar-agent: Route traffic to backend sync service based on policy
Note left of flagd-provider: In most cases the connection made to <br> `localhost` data plane port <br> e.g. localhost:9211
flagd-provider-->flagd-sync.service: Get realtime flag update over gRPC stream
Note left of proxy-sidecar-agent: Based on the host header i.e. authority <br> the tarrfic was then routed <br> backend service.
loop
flagd-provider->>flagd-provider: in-memory cache
end
application-->>flagd-provider: Check the state of a feature flag
flagd-provider-->>application: Get the feature flag from in-memory cache <br/> run the evaluation logic and return final state
```

**Note:** There is small variation in supported alternative resolver e.g. java support `zooKeeper`

## Motivation
Expand All @@ -59,51 +37,41 @@ provided by gRPC core*.

The idea is to

- allow a new config option to pass the [target](https://grpc.io/docs/guides/custom-name-resolution/#life-of-a-target-string) string
- reduce need to create/override existing implementations to simplify use of name-resolver
* allow a new config option to pass the [target](https://grpc.io/docs/guides/custom-name-resolution/#life-of-a-target-string) string
* reduce need to create/override existing implementations to simplify use of name-resolver

### Target String Pattern*

There is no restriction on naming but the string most comply with below standard
Below is an example of a custom target string which will use envoy sidecar proxy for name resolution

```text
scheme://authority/endpoint_name
envoy://localhost:9211/flagd-sync.service
```

#### Scheme Suggestions

We can choose our own scheme considering it's not used in gRPC core
The custom name resolver provider in this case will use the endpoint name i.e. `flagd-sync.service` as [authority](https://github.com/grpc/grpc-java/blob/master/examples/src/main/java/io/grpc/examples/nameresolve/ExampleNameResolver.java#L55-L61)
and connect to `localhost:9211`

| Scheme | Comment | Status |
|--------------------|---------|--------------------|
| **flagd://** | | Approved / Reject |
| **grpc-remote://** | | Approved / Reject |
| **tbd** | | Approved / Reject |

##### Authority

Authority needs to be a valid tcp endpoint of proxy/service discovery agent (passed by the user)
e.g. `localhost:9211`

##### Endpoint Name

The endpoint also specific to user deployment environment which define the `flagd` or `sync` backend
service name i.e. VirtualHost. This is used by the provided authority i.e. proxy service where to
route the traffic e.g.
```mermaid
sequenceDiagram
participant application
participant flagd-provider
participant proxy-sidecar-agent
participant flagd-sync.service
```shell
$ grpcurl -vv -plaintext -authority flagd-sync.service 127.0.0.1:9211 list flagd.sync.v1.FlagSyncService
flagd.sync.v1.FlagSyncService.FetchAllFlags
flagd.sync.v1.FlagSyncService.GetMetadata
flagd.sync.v1.FlagSyncService.SyncFlags
application->>flagd-provider: Check the state of a feature flag
flagd-provider-->>application: Get the feature flag from in-memory cache <br/> run the evaluation logic and return final state
loop
flagd-provider->>flagd-provider: in-memory cache
end
flagd-provider->>proxy-sidecar-agent: gRPC stream connection
proxy-sidecar-agent-->>flagd-provider:
Note right of flagd-provider: Instead host:port target string <br> "envoy://localhost:9211/flagd-sync.service" <br> will be used
proxy-sidecar-agent->>flagd-sync.service: Apply required policy and route traffic <br> to backend nodes
flagd-sync.service-->>proxy-sidecar-agent:
Note right of proxy-sidecar-agent: Policy and route rules are applied based <br> on `authority` header used by the <br> gRPC client
```

##### Samples

* ``[ flagd || grpc-remote ]://[ 127.0.0.1:9211 ]/[ flagd-sync.service ]``
* ``[ flagd || grpc-remote ]://[ proxy.domain:443 ]/[ flagd-sync.service ]``

##### Drawbacks
#### Drawbacks

* One of the big drawback was limited support of the language only `java` and `golang`
* Will introduce inconsistent user experience
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