Access Go Api Hosted in Docker container

Question

I have created a Go backend server that contains an api. All works well when running locally "go run server". I did however encounter issues when running it in docker. So I created a Dockerfile and run the linux container in networkmode host but can't access the api in the browser. If it's working I should be able to see a json response from http://localhost:8500/status. So I'm thinking I need permissions or add flags or more installation related scripts. I have been testing different flags and ports in docker but can't identify the issue. See code, dockerfile and command below.

Note: When I run the program locally on windows a security warning pops up, perhaps this is related to the issue?

I'm running docker desktop community v 2.2.0.5 stable.

Api code:

import (
    "log"
    "net/http"
    conf "server/conf"

    "github.com/gorilla/mux"
    "github.com/jinzhu/gorm"
    _ "github.com/jinzhu/gorm/dialects/mysql"
)
var db *gorm.DB

// Middleware used to add correct permissions for all requests
func middleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("Content-Type", "application/json")
        w.Header().Set("Access-Control-Allow-Origin", "*")
        w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
        next.ServeHTTP(w, r)
    })
}

func StartApi(config conf.Config, _db *gorm.DB) {

log.Println("Start Api")
    db = _db

    router := mux.NewRouter()
    // Create 
    router.HandleFunc("/login", login).Methods("POST", "OPTIONS")
    router.HandleFunc("/network", createNetwork).Methods("POST", "OPTIONS")

    // Read 
    router.HandleFunc("/users/{networkName}", getUsers).Methods("GET", "OPTIONS")
    router.HandleFunc("/streams/{networkName}", getStreams).Methods("GET", "OPTIONS")
    router.HandleFunc("/status", showStatus).Methods("GET", "OPTIONS")

    log.Println("API started at port " + config.Backend.Api_port) // api port is stored in config
    log.Println(http.ListenAndServe(":"+config.Backend.Api_port, middleware(router)))

    log.Println("Api done!")  }

Dockerfile:

# Start from the latest golang base image
FROM golang:latest

WORKDIR /go/src/server

COPY ./src/server .

# Download packages
RUN go get . 

# Compile code
#RUN go build -o server
RUN go install server

# Expose ports
EXPOSE 8500
EXPOSE 8600

#ENTRYPOINT ./server
CMD ["go", "run", "server"]

Docker-compose:

version : '3'

services:
  react:
    build: ./ReactFrontend/
    container_name: ReactFrontend
    tty: true
    ports:
    - 4000:3000

  backend:
    network_mode: host
    build: ./GoBackend/
    container_name: goserver
    ports:
    - 8500:8500
    - 8600:8600

Docker command:

docker run --net=host goserver

Any help is appreciated,

Cheers!

Answer 1

So i solved it for now by:

As mentioned here: https://docs.docker.com/compose/networking/

Add to docker-compose:

networks:
  default:
    external:
      name: database_default

As mentioned here: Access to mysql container from other container

I can connect to database as < db_container_name >:3306 in backend.

To automate the process I created a .sh script for handling an extra setup config step on container start. However, due to my structure in my config.yml it was hard to update with just "sed" commands so I created a python program for updating all config data. The Dockerfile, docker-compose file, setup.sh and update_config.py file is shown below.

setup.sh:

#!/bin/bash
# Don't remove this!
# This file is used by dockerfile to replace configs

# Replace config on run
python3 update_config.py

# Start program
go run server

Dockerfile:

# Start from the latest golang base image
FROM golang:latest

WORKDIR /go/src/server

COPY ./src/server .

# Install python3 and yml compability
RUN apt-get update && apt-get install -y python3-pip
RUN python3 --version
RUN pip3 install PyYAML

# Download packages
RUN go get . 

# Compile code
#RUN go build -o server
RUN go install server

# Expose ports
EXPOSE 8500
EXPOSE 8600

# ENV
 ENV DB_HOST "mysql:3306"

#CHMOD setup
RUN chmod +x setup.sh

CMD ["./setup.sh"]

Docker-compose

version : '3'

services:
  react:
    build: ./ReactFrontend/
    container_name: ReactFrontend
    tty: true
    ports:
    - 4000:3000

  backend:
    build: ./GoBackend/
    container_name: GoBackend
    environment:
      DB_HOST: mysql:3306 # Name or IP of DB container!
    ports:
    - 8500:8500
    - 8600:8600

networks:
  default:
    external:
      name: database_default

update_config.py:

import yaml
import os

"""
DONT REMOVE
This file is used in the dockerfile!
"""

fname = "/go/src/server/config.yml"

stream = open(fname, 'r')
data = yaml.safe_load(stream)
stream.close()

# Add more updates here!
if os.environ.get('DB_HOST') is not None:
    data["database"]["ip"] = os.environ['DB_HOST']


# Updated data print
print("Updated Data", data)

# Write changes to config
stream = open(fname, 'w')
yaml.dump(data, stream)
stream.close()

Example docker command that now works if we only want container to run:

docker run -p 8500:8500 -p 8600:8600 --net database_default goserver

It is working fine! And we are avoiding using unnecessary host network mode!