Mit Docker-Compose kann nicht auf die Go-REST-API zugegriffen werden

version: '3'
services:
  app:
    container_name: full_app
    build: .
    ports:
      - 8080:8080
    expose:
      - 8080
    restart: on-failure
    environment:
      - pma_host=fullstack-mysql
      - db_name=${db_name}
      - db_user=${db_user}
      - db_password=${db_port}
    volumes:
      - .:/usr/src/app/
    depends_on:
      - fullstack-mysql
    networks:
      - fullstack

  fullstack-mysql:
    image: mysql:5.7
    container_name: full_db_mysql
    ports:
      - 3306:3306
    environment:
      - mysql_root_host=${db_host}
      - mysql_user=${db_user}
      - mysql_root_user=${db_root_user}
      - mysql_password=${db_password}
      - mysql_root_password=${db_root_password}
      - mysql_database=${db_name}
      - mysql_root_password=${db_password}
    volumes:
      - database_mysql:/var/lib/mysql
    networks:
      - fullstack

  phpmyadmin:
    image: phpmyadmin/phpmyadmin
    container_name: phpmyadmin_container
    depends_on:
      - fullstack-mysql
    environment:
      - pma_host=fullstack-mysql
      - pma_user=${db_user}
      - pma_port=${db_port}
      - pma_password=${db_password}
    ports:
      - 9090:80
    restart: always
    networks:
      - fullstack

volumes:
  api:
  database_mysql:

# networks to be created to facilitate communication between containers
networks:
  fullstack:
    driver: bridge

# start from golang base image
from golang:alpine as builder

# env go111module=on

# install git.
# git is required for fetching the dependencies.
run apk update && apk add --no-cache git

# set the current working directory inside the container
workdir /app

# copy go mod and sum files
copy go.mod go.sum ./

# download all dependencies. dependencies will be cached if the go.mod and the go.sum files are not changed
run go mod download

# copy the source from the current directory to the working directory inside the container
copy . .

# build the go app
run cgo_enabled=0 goos=linux go build -a -installsuffix cgo -o main .

# start a new stage from scratch
from alpine:latest
run apk --no-cache add ca-certificates

workdir /root/

# copy the pre-built binary file from the previous stage. observe we also copied the .env file
copy --from=builder /app/main .
copy --from=builder /app/.env .

# expose port 8080 to the outside world
expose 8080

#command to run the executable
cmd ["./main"]

package main

import (
    "github.com/gin-gonic/gin"
    "log"
    "net/http"
)

func main() {
    router := gin.Default()

    router.GET("/", func(context *gin.Context) {
        context.JSON(http.StatusOK, gin.H{"data": "Hello World !"})
    })

    router.Run("localhost:8080")
}

router.Run("0.0.0.0:8080")