title: Overview - Pluggable Architecture - Quorum

The Quorum client is a modified `geth` client. One of the unique enhancements
is the pluggable architecture which allows adding additional features as plugins to the core `geth`, 
providing extensibility, flexibility, and isolation of Quorum features.

## Benefits
 
This enhancement provides a number of benefits, including:

1. Allowing the implementation of certain components of the Quorum client to be changed at configuration time.
1. Supporting our community to improve the Quorum client with their own innovative implementations of the supported pluggable components.
1. Decoupling new Quorum-specific features from core `geth` thereby simplifying the process of pulling in changes from upstream `geth`.

## How it works?

Each plugin exposes an implementation for a specific [plugin interface](https://github.com/jpmorganchase/quorum-plugin-definitions) (or see `Pluggable Architecture -> Plugins` for more details)
Plugins are executed as a separate process and communicate with the main Quorum client `geth` process
over a [gRPC](https://grpc.io/) interface.

The plugin implementation must adhere to certain gRPC services defined in a `.proto` file corresponding to the plugin interface.
Plugins can be written in different languages as gRPC provides a mechanism to generate stub code from `.proto` files. 

The network communication and RPC are handled automatically by the [high-level plugin library](https://github.com/hashicorp/go-plugin).

## Installing Plugins

Currently plugins must be manually installed into a directory (defaults to `plugins` directory inside `geth` data directory - default can be overriden by setting `baseDir` in [plugins settings](../Settings)).
 
## Using Plugins

[Plugins settings file](../Settings) contains a JSON that describes what plugins to be used.
Then start `geth` with `--plugins` as below:

```bash
geth ... \
     --plugins file:///<path>/<to>/plugins.json
```

## Plugin Integrity Verification

Plugin Central Server can be used to download and verify plugin integrity using [PGP](https://en.wikipedia.org/wiki/Pretty_Good_Privacy). 
The architecture enables the same verification process locally via `--plugins.localverify` and `--plugins.publickey` flags or 
remotely with custom plugin central - reference the [`Settings`](../Settings/) section for more information on how to support custom plugin central. 

If the flag `--plugins.skipverify` is provided at runtime the plugin verification process will be disabled.

!!! warning
    Using `--plugins.skipverify`  is not advised for production settings and it should be avoided as it introduces security risks.

## Example: `HelloWorld` plugin

The plugin interface is implemented in Go and Java. In this example, `HelloWorld` plugin exposes a JSON RPC endpoint 
to return a greeting message in the configured language.
This plugin is [reloadable](../Internals/#plugin-reloading). It means that the plugin can take changes from its JSON configuration.  

### Build plugin distribution file   

1. Clone plugin repository
   ```bash
   › git clone --recursive https://github.com/jpmorganchase/quorum-plugin-hello-world.git
   › cd quorum-plugin-hello-world
   ```
1. Here we will use Go implementation of the plugin
   ```bash
   quorum-plugin-hello-world› cd go
   quorum-plugin-hello-world/go› make
   ```
   `quorum-plugin-hello-world-1.0.0.zip` is now created in `build` directory. 
   Noticed that there's a file `hello-world-plugin-config.json` which is the JSON configuration file for the plugin.

### Start Quorum with plugin support

1. Build Quorum
   ```bash
   › git clone https://github.com/jpmorganchase/quorum.git
   › cd quorum
   quorum› make geth
   ```
1. Copy `HelloWorld` plugin distribution file and its JSON configuration `hello-world-plugin-config.json` to `build/bin`
1. Create `geth-plugin-settings.json`
   ```
   quorum› cat > build/bin/geth-plugin-settings.json <<EOF
   {
     "baseDir": "./build/bin",
     "providers": {
       "helloworld": {
         "name":"quorum-plugin-hello-world",
         "version":"1.0.0",
         "config": "file://./build/bin/hello-world-plugin-config.json"
       }
     }
   }
   EOF
   ```
1. Run `geth` with plugin
   ```bash
   quorum› PRIVATE_CONFIG=ignore \
   geth \
        --nodiscover \
        --verbosity 5 \
        --networkid 10 \
        --raft \
        --raftjoinexisting 1 \
        --datadir ./build/_workspace/test \
        --rpc \
        --rpcapi eth,debug,admin,net,web3,plugin@helloworld \
        --plugins file://./build/bin/geth-plugin-settings.json \
        --plugins.skipverify
   ```
   `ps -ef | grep helloworld` would reveal the `HelloWorld` plugin process

### Test the plugin

1. Call the JSON RPC
   ```bash
   quorum› curl -X POST http://localhost:8545 \
        -H "Content-type: application/json" \
        --data '{"jsonrpc":"2.0","method":"plugin@helloworld_greeting","params":["Quorum Plugin"],"id":1}'
   {"jsonrpc":"2.0","id":1,"result":"Hello Quorum Plugin!"}
   ```
1. Update plugin config to support `es` language
   ```bash
   # update language to "es"
   quorum› vi build/bin/hello-world-plugin-config.json
   ```
1. Reload the plugin
   ```bash
   quorum› curl -X POST http://localhost:8545 \
        -H "Content-type: application/json" \
        --data '{"jsonrpc":"2.0","method":"admin_reloadPlugin","params":["helloworld"],"id":1}'
   {"jsonrpc":"2.0","id":1,"result":true}
   ```
1. Call the JSON RPC
   ```bash
   quorum› curl -X POST http://localhost:8545 \
        -H "Content-type: application/json" \
        --data '{"jsonrpc":"2.0","method":"plugin@helloworld_greeting","params":["Quorum Plugin"],"id":1}'
   {"jsonrpc":"2.0","id":1,"result":"Hola Quorum Plugin!"}
   ```