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@ -286,61 +286,6 @@ func main() {
It's that simple.
## How it works
<p align="center">
<img src="go-micro.png" />
</p>
Go Micro is a framework that addresses the fundamental requirements for writing microservices.
Let's dig into the core components.
### Registry
The registry provides a service discovery mechanism to resolve names to addresses. It can be backed by consul, etcd, zookeeper, dns, gossip, etc.
Services should register using the registry on startup and deregister on shutdown. Services can optionally provide an expiry TTL and reregister
on an interval to ensure liveness and that the service is cleaned up if it dies.
### Selector
The selector is a load balancing abstraction which builds on the registry. It allows services to be "filtered" using filter functions and "selected"
using a choice of algorithms such as random, roundrobin, leastconn, etc. The selector is leveraged by the Client when making requests. The client
will use the selector rather than the registry as it provides that built in mechanism of load balancing.
### Transport
The transport is the interface for synchronous request/response communication between services. It's akin to the golang net package but provides
a higher level abstraction which allows us to switch out communication mechanisms e.g http, rabbitmq, websockets, NATS. The transport also
supports bidirectional streaming. This is powerful for client side push to the server.
### Broker
The broker provides an interface to a message broker for asynchronous pub/sub communication. This is one of the fundamental requirements of an event
driven architecture and microservices. By default we use an inbox style point to point HTTP system to minimise the number of dependencies required
to get started. However there are many message broker implementations available in go-plugins e.g RabbitMQ, NATS, NSQ, Google Cloud Pub Sub.
### Codec
The codec is used for encoding and decoding messages before transporting them across the wire. This could be json, protobuf, bson, msgpack, etc.
Where this differs from most other codecs is that we actually support the RPC format here as well. So we have JSON-RPC, PROTO-RPC, BSON-RPC, etc.
It separates encoding from the client/server and provides a powerful method for integrating other systems such as gRPC, Vanadium, etc.
### Server
The server is the building block for writing a service. Here you can name your service, register request handlers, add middeware, etc. The service
builds on the above packages to provide a unified interface for serving requests. The built in server is an RPC system. In the future there maybe
other implementations. The server also allows you to define multiple codecs to serve different encoded messages.
### Client
The client provides an interface to make requests to services. Again like the server, it builds on the other packages to provide a unified interface
for finding services by name using the registry, load balancing using the selector, making synchronous requests with the transport and asynchronous
messaging using the broker.
The above components are combined at the top-level of micro as a **Service**.
## Plugins
By default go-micro only provides a few implementation of each interface at the core but it's completely pluggable. There's already dozens of plugins which are available at [github.com/micro/go-plugins](https://github.com/micro/go-plugins). Contributions are welcome!
@ -374,6 +319,64 @@ Flag usage of plugins
service --registry=etcdv3 --transport=nats --broker=kafka
```
## Wrappers
Go-micro includes the notion of middleware as wrappers. The client or handlers can be wrapped using the decorator pattern.
### Handler
Here's an example service handler wrapper which logs the incoming request
```
// implements the server.HandlerWrapper
func logWrapper(fn server.HandlerFunc) server.HandlerFunc {
return func(ctx context.Context, req server.Request, rsp interface{}) error {
fmt.Printf("[%v] server request: %s", time.Now(), req.Method())
return fn(ctx, req, rsp)
}
}
```
It can be initialised when creating the service
```
service := micro.NewService(
micro.Name("greeter"),
// wrap the handler
micro.WrapHandler(logWrapper),
)
```
### Client
Here's an example of a client wrapper which logs requests made
```
type logWrapper struct {
client.Client
}
func (l *logWrapper) Call(ctx context.Context, req client.Request, rsp interface{}, opts ...client.CallOption) error {
fmt.Printf("[wrapper] client request to service: %s method: %s\n", req.Service(), req.Method())
return l.Client.Call(ctx, req, rsp)
}
// implements client.Wrapper as logWrapper
func logWrap(c client.Client) client.Client {
return &logWrapper{c}
}
```
It can be initialised when creating the service
```
service := micro.NewService(
micro.Name("greeter"),
// wrap the client
micro.WrapClient(logWrap),
)
```
## Other Languages
Check out [ja-micro](https://github.com/Sixt/ja-micro) to write services in Java