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Registry

Registry is a simple service registry that uses the consistent hashing algorithm for service discovery.

What is consistent hashing

Consistent hashing is a hashing technique that performs really well when operated in a dynamic environment where the distributed system scales up and scales down frequently.

Consistent Hashing allows distributing data in such a way that minimize reorganization when nodes are added or removed, hence making the system easier to scale up or down.

The key idea is that it's a distribution scheme that DOES NOT depend directly on the number of servers.

In Consistent Hashing, when the hash table is resized, in general only k / n keys need to be remapped, where k is the total number of keys and n is the total number of servers.

When a new node is added, it takes shares from a few hosts without touching other's shares When a node is removed, its shares are shared by other hosts.

Getting started

Build registry

cd cmd 
go build -o registry

Usage

   -id string
        Service ID, cannot be empty
  -bind string
        The address used to register the service (default ":7370").
  -bind-advertise string
        The address will advertise to other services (default ":7370").
  -addr string
        The address used for service discovery (default ":9800").
  -advertise string
        The address will advertise to client for service discover (default ":9800").
  -registries string
        Registry server addresses, it can be empty, and multiples are separated by commas.
  

Starting registry server

To start a registry server, follow these steps:

1. Determine the number of nodes required based on your actual situation.
2. Execute the following commands to start the nodes:

# Starting the first node
./registry -bind=":7370" \
     -bind-advertise="172.16.3.3:7370" \
     -id=service-1 \
     -addr=":9800" \
     -advertise="172.16.3.3:9800"

# Starting the second node
# The second one has an additional parameter -registries="172.16.3.3:7370",
# because the second node needs to register with the first one
./registry -bind=":7371" \
     -bind-advertise="172.16.3.3:7371" \
     -id=service-2 \
     -registries="172.16.3.3:7370" \
     -addr=":9801" \
     -advertise="172.16.3.3:9801"

Note: If there is a firewall, make sure to open both TCP and UDP on advertise ports.

Register services

Use the following code snippet to register services:

// Create a new registration object
r := register.New(id, bind, advertise, registries, group, addr)

// Start the registration
err = r.Start()
if err != nil {
	panic(err)
}

Parameters:

• id: Service ID.
• bind: Address used to register the service to the registry server.
• advertise: Address that the service will advertise to the registry server. Can be used for basic NAT traversal where both the internal IP:port and external IP:port are known.
• registries: Addresses of the registry server(s). If there are more than one, separate them with commas, such as "192.168.1.101:7370,192.168.1.102:7370".
• group: Group name the current service belongs to.
• addr: Address currently provided by this service to the client. For example, if the current service is an HTTP server, the address is 172.16.3.3:80, which is the address that HTTP listens to.

Service Discovery

Usage

// You can choose any one of the registered servers.
registryAddr := "172.16.3.3:9801"
group := "test-group"

// Create a new RpcClient
client, err := client.NewRpcClient(registryAddr)
if err != nil {
	panic(err)
}

// Use consistent hash to assign services based on user ID
service, err := client.Match(groupName, "user-id-1")
if err != nil {
	panic(err)
}

log.Printf("[INFO] Matched key: %s, Service ID: %s, Service Address: %s\n", key, service.Id, service.Addr)

// Get all services of the group
allService, err := client.Members(group)
if err != nil {
      log.Printf("[ERROR] Failed to get all services: %s\n", err)
}
log.Printf("[INFO] All services: %+v\n", allService)

Examples

Register two web services.

# Register the first web service.
cd examples/service
go build -o webservice webservice.go 
./webservice \
	-group=webservice-group \
	-id=webserver1 \
	-registries=172.16.3.3:7370 \
	-bind=":8370" \
	-advertise="172.16.3.3:8370" \
	-addr="172.16.3.3:8080"

# Register the second web service.
cd examples/service
./webservice \
	-group=webservice-group \
	-id=webserver2 \
	-registries=172.16.3.3:7370 \
	-bind=":8371" \
	-advertise="172.16.3.3:8371" \
	-addr="172.16.3.3:8081"

Client discovery service

cd examples/client
go build -o client main.go
./client