Connecting Golang and Postgres docker containers

Question

I'm trying to run a golang server at localhost:8080 that uses a postgres database. I've tried to containerize both the db and the server but can't seem to get them connected.

main.go

func (a *App) Initialize() {
    var db *gorm.DB
    var err error
    envErr := godotenv.Load(".env")
    if envErr != nil {
        log.Fatalf("Error loading .env file")
    }
    var dbString = fmt.Sprintf("port=5432 user=sample dbname=sampledb sslmode=disable password=password host=db")
    
    db, err = gorm.Open("postgres", dbString)
    if err != nil {
        fmt.Printf("failed to connect to databse\n",err)
    }
    a.DB=model.DBMigrate(db)
    a.Router = mux.NewRouter()
    a.setRoutes()
}

//Get : get wrapper
func (a *App) Get(path string, f func(w http.ResponseWriter, r *http.Request)) {
    a.Router.HandleFunc(path, f).Methods("GET")
}

//Post : post wrapper
func (a *App) Post(path string, f func(w http.ResponseWriter, r *http.Request)) {
    a.Router.HandleFunc(path, f).Methods("POST")
}

//Run : run on port
func (a *App) Run(port string) {
    handler := cors.Default().Handler(a.Router)
    log.Fatal(http.ListenAndServe(port, handler))
}

func (a *App) setRoutes() {
    a.Get("/", a.handleRequest(controller.Welcome))
    a.Get("/users", a.handleRequest(controller.GetUsers))
    a.Get("/user/{id}", a.handleRequest(controller.GetUser))
    a.Post("/login", a.handleRequest(controller.HandleLogin))
    a.Post("/users/add", a.handleRequest(controller.CreateUser))
    a.Post("/validate", a.handleRequest(controller.HandleValidation))
}

func main() {
    app := &App{}
    app.Initialize()
    app.Run(":8080")

}

server Dockerfile

FROM golang:latest

RUN mkdir /app
WORKDIR /app/server

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

docker-compose.yml

version: '3.7'
services:
    db:
        image: postgres
        container_name: ep-db
        environment:
            - POSTGRES_PORT=${DB_PORT}
            - POSTGRES_USER=${DB_USERNAME}  
            - POSTGRES_PASSWORD=${DB_PASSWORD}
            - POSTGRES_DB=${DB_NAME}
            
        ports:
            - '5432:5432'
        volumes:
            - ./db:/var/lib/postgresql/data"
        networks:
            - internal
    server:
        container_name: ep-server
        build:
            context: ./server
            dockerfile: Dockerfile
        command: bash -c "go build && ./server -b 0.0.0.0:8080 --timeout 120"
        volumes:
            - './server:/app/server'
        expose:
            - 8080
        depends_on: 
            - db
        networks:
            - internal
        stdin_open: true
volumes:
    db:  
    server:
networks:
    internal:
      driver: bridge

I have some get and post requests that return the right values when i run it locally on my computer (for ex. localhost:8080/users would return a JSON full of users from the database) but when I use curl inside the server container, I don't get any results. I am new to docker, Is there something wrong with what I'm doing so far?

Answer 1

Each docker container has its own IP address. When you connect to the postgres db from your application, you are using localhost , which is the container for the application and not the db. Based on your docker-compose, you should use the hostname db (the service name) to connect to the database.

Answer 2

As suggested by @DavidMaze you should verify the logs from your server container. Also,

1. First ensure ep-server is running (check that the output of docker container ls has status running for ep-server )
2. Run docker logs ep-server to view errors (if any)
3. If there are no errors in the logs, then run a docker exec -it ep-server bash to login to your container and run a telnet ep-db 5432 to verify that your postgres instance is reacheable from ep-server