util/addr: Fixes findIP to return the correct public IP

[guillaumebour]

When run on a host with no private IP, but with a public IP available, go-micro incorrectly figures out its service's address and uses the loopback address. This is due to the findIP function in utils/addr returning the wrong IP address when run on a host with a Public IP and no Private IP, leading to go-micro advertising the wrong address for its service (e.g. when using etcd as the registry).

What was done

• Update util/addr_test.go with a test for findIP.
• Update findIP to return the first public IP (if available) if no private IP is available.
• Update findIP to return the first loopback IP (if available) if no public IP is available.
• Fix typos in the Extract function documentation.

How to reproduce the initial issue

To reproduce the initial issue, you can setup a docker-compose with etcd and a go-micro service and check the information available in etcd.

Details

Step 1. Create a go-micro app with the following main.go:

package main

import (
	"context"
	"fmt"
	"go-micro.dev/v4"
	"os"

        _ "github.com/go-micro/plugins/v4/registry/etcd"
)

type Request struct {
	Name string `json:"name"`
}

type Response struct {
	Message string `json:"message"`
}

type Helloworld struct{}

func (h *Helloworld) Greeting(ctx context.Context, req *Request, rsp *Response) error {
	rsp.Message = "Hello " + req.Name
	return nil
}

func main() {
	serviceName := os.Getenv("SERVICE_NAME")

	fmt.Printf("--- Starting %s ---\n", serviceName)

	// create a new service
	service := micro.NewService(
		micro.Name(serviceName),
		micro.Handle(new(Helloworld)),
	)

	// initialise flags
	service.Init()

	// start the service
	err := service.Run()
	if err != nil {
		return
	}
}

Step 2. Use the following Dockerfile to build the application's image with the tag helloworld:latest:

# syntax=docker/dockerfile:1
FROM golang:1.20 as builder

WORKDIR /app

COPY go.mod go.sum ./
RUN go mod download

COPY . .

RUN CGO_ENABLED=0 GOOS=linux go build -o helloworld

FROM debian

WORKDIR /app

COPY --from=builder /app/helloworld /bin/helloworld

CMD ["/bin/helloworld"]

Step 3. Use the following docker-compose.yaml to deploy etcd alongside the app:

version: "3"
services:
  etcd-test:
    container_name: etcd-test
    image: bitnami/etcd:latest
    environment:
      - ALLOW_NONE_AUTHENTICATION=yes
    networks:
      test_net:
        ipv4_address: 109.0.0.8
  helloworld1:
    container_name: helloworld
    image: helloworld:latest
    environment:
      - SERVICE_NAME=helloworld-1
      - MICRO_SERVER_ADDRESS=:8080
      - MICRO_REGISTRY=etcd
      - MICRO_REGISTRY_ADDRESS=etcd-test:2379
    depends_on:
      - etcd-test
    networks:
      test_net:
        ipv4_address: 109.0.0.10
networks:
  test_net:
    ipam:
      driver: default
      config:
        - subnet: 109.0.0.0/24

Step 4. Use the following command to get the address advertised by the service:

docker exec -it etcd-test "/opt/bitnami/etcd/bin/etcdctl" get "" --prefix | sed -n '2 p' | jq '.nodes | first.address'

With the docker network setup with a public IP range, it will be: "127.0.0.1:8080", while without, it will use the container private IP.

[jochumdev]

Hi Guillaume,

This is great work! Many thanks.

Kind regards,
René