Use gRPC to communicate between containers

I'm implementing two services (server and client) running on two different containers and trying to use gRPC to communicate between them.

If I deploy the server as a container and run the client not on a container, everything works just fine. But if I deploy the client on a different container I get Error #01: could not retrieve restaurant's list: rpc error: code = Unavailable desc = grpc: the connection is unavailable error.

What steps am I missing to communicate two different containers using gRPC?

PS: I would like to try without Kubernetes for now.

SERVER

func Serve() {

	log.Println("serving...")

	port := ":50051"

	lis, err := net.Listen("tcp", port)
	if err != nil {
		log.Fatalf("failed to listen on port %s: %v", port, err)
	}

	s := grpc.NewServer()
	server := server{}
	RegisterNeo4BaconServer(s, server)

	if err := s.Serve(lis); err != nil {
		log.Fatal("could not serve: ", err)
	}
}

Makefile

image: ## build docker image and push image to registry
	@docker build -t neo4bacon -f resources/prod/Dockerfile .

run: ## deploy application container
	@docker run --rm -d --name neo4bacon neo4bacon

CLIENT

func Get() (*api.RestaurantList, error) {
	// Neo4bacon backend
	backendPort := ":50051"

	conn, err := grpc.Dial(backendPort, grpc.WithInsecure())
	if err != nil {
		&api.RestaurantList{}, fmt.Errorf("could not connect to backend %s: %s", backendPort, err)
	}
	defer conn.Close()

	client := api.NewNeo4BaconClient(conn)

	restaurantList, err := client.List(context.Background(), &api.Empty{})
	if err != nil {
		return &api.RestaurantList{}, fmt.Errorf("could not retrieve restaurant's list: %s", err)
	}
	return restaurantList, nil
}

Makefile

image: ## build docker image and push image to registry 	
@docker build -t alesr/bacon-api -f resources/prod/Dockerfile . 	

run: ## deploy docker container 	
@docker run --rm -d -p 8080:8080 --name bacon-api bacon-api

You need to include the hostname in the dial function, otherwise it's looking at localhost which is unique to each container (docker creates a separate networking namespace for containers by default). Change the following:

backendPort := "neo4bacon:50051"

Edit: you also need to setup a network and connect the containers to that network because the default bridge does not include DNS discovery:

docker network create baconnet
docker run --rm -d --net baconnet --name neo4bacon neo4bacon
docker run --rm -d --net baconnet -p 8080:8080 --name bacon-api bacon-api

If your gRPC client and server are hosted on docker, to establish the connection between to container you should follow the below steps.

1. First, you should create a docker network.

   docker network create web_server --driver bridge

2. Then register your containers with the created network. You should mention the service name and the network in the docker run command.

   docker run -dit -p 3000:3000 --name question-service --network web_server ${{ env.REGISTRY }}/question-service:latest

3. Now your URL should format as below,

> {{service-name}}:port

as an example

question-service:3000

for more details, you can refer to this blog