Go app (in docker container) not reflecting changes on page?

I'm new to Go, but having an annoying issue where changes in the code are not reflected on the page, unless I do another --build when I bring up the container. Is this normal? I'm running`Windows 10, Go 1.19, AMD, Docker Desktop/Compose.

If I change "Hello, World!" to some other string, CTRL+C the running app, and then run docker-compose up, the changes are NOT reflected on the page, even after clearing browser cache and using an incognito window. HOWEVER, if I run docker-compose up --build, the changes WILL be reflected.

Reminder I'm new to Go, but is this normal behaviour? Do I have to re-build the project in docker-compose each time to see the changes? Or do you see anything "off" in my code? I'm following a few year old Udemy course, so of course every step there's a new "thing" to troubleshoot as it doesn't work as shown eye roll

They suggest using Air for hot-reloading, which I'm also having an issue with as IT'S not working either, however I've opened a GitHub issue for that.

Here is the code from the various files:

main.go

package main

import (
	"ambassador/src/database"

	"github.com/gofiber/fiber/v2"
)

func main() {

	// Connect to the database
	database.Connect()

	// Migrate tables in the database
	database.AutoMigrate()

	// Create a new fiber app, which is based on Express.js
	app := fiber.New()

	app.Get("/", func(c *fiber.Ctx) error {
		return c.SendString("Hello, World!")
	})

	app.Listen(":3000")
}

Dockerfile

FROM golang:1.19

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

COPY . .

# Use air for live go hot-reloading
# This one doesn't work, use go install instead
# RUN curl -sSfL https://raw.githubusercontent.com/cosmtrek/air/master/install.sh | sh -s -- -b $(go env GOPATH)/bin

# Air does not work for me. Opening github issue. Skip for now
# RUN go install github.com/cosmtrek/air@latest
# CMD ["air"]

CMD ["go", "run", "main.go"]

docker-compose.yaml

version: '3.9'
services:
    backend:
        build: .
        ports:
            - 8000:3000
        # volumes:
        #   - .:/app
        depends_on:
            - db

    db:
        image: mysql:5.7.22
        restart: always
        environment:
            MYSQL_DATABASE: ambassador
            MYSQL_USER: root
            MYSQL_PASSWORD: root
            MYSQL_ROOT_PASSWORD: root
        volumes:
            - .dbdata:/var/lib/mysql
        ports:
            - 33066:3306

src > database > db.go

package database

import (
	"ambassador/src/models"

	"gorm.io/driver/mysql"
	"gorm.io/gorm"
)

var DB *gorm.DB

func Connect() {
	var err error
	DB, err = gorm.Open(mysql.Open("root:root@tcp(db:3306)/ambassador"), &gorm.Config{})

	if err != nil {
		panic("Could not connect with the database!")
	}
}

func AutoMigrate() {
	DB.AutoMigrate(models.User{})
}

src > models > user.go

package models

type User struct {
	Id           uint
	FirstName    string
	LastName     string
	Email        string
	Password     string
	IsAmbassador bool
}

go.mod

module ambassador

go 1.19

require github.com/gofiber/fiber/v2 v2.36.0

require (
	github.com/andybalholm/brotli v1.0.4 // indirect
	github.com/go-sql-driver/mysql v1.6.0 // indirect
	github.com/jinzhu/inflection v1.0.0 // indirect
	github.com/jinzhu/now v1.1.5 // indirect
	github.com/klauspost/compress v1.15.0 // indirect
	github.com/valyala/bytebufferpool v1.0.0 // indirect
	github.com/valyala/fasthttp v1.38.0 // indirect
	github.com/valyala/tcplisten v1.0.0 // indirect
	golang.org/x/sys v0.0.0-20220227234510-4e6760a101f9 // indirect
	gorm.io/driver/mysql v1.3.5 // indirect
	gorm.io/gorm v1.23.8 // indirect
)

The same code is included in this screenshot of my IDE.

Go isn’t a script language and needs in rebuild and restart application to apply changes

You can use Golang fresh for rebuild and restart your app

https://github.com/gravityblast/fresh

Add this to your Dockerfile

RUN go install github.com/pilu/fresh@latest
...
CMD [ "fresh" ]

You are not mounting any files into your container, only copying them once on image build. This is why you are not seeing anychanges unless you build, or copy new files into the container.

You've already commented out a volume from your docker-compose.yaml, but if you uncomment those lines you should see that changes are reflected without rebuilding.

To answer your original question — NO, you DO NOT need to add the --build tag when running up your docker-compose file. It doesn't relate to Go, it relates only to docker containers working logic.

If we come to the live-reload problem then the problem is with the technology docker uses for file sharing between a host system and containers.

I have had the same issues on mac when tried to use not the Docker Desktop but an alternative like Rancher which even uses docker CLI via moby. When I switched back to the original Docker Desktop which uses gRPC FUSE, osxfs, and VirtioFS — with all of them worked like a charm.

I don't know how this feature is implemented on windows, but I'm sure you could dig into this direction.