$GOPATH/go.mod exists but should not on Docker - mysql

Question

I'm trying to build a Docker container that contains both MySQL and a Go server.
Just importing the MySQL libraries cause the error.
Any pointers to what I'm doing wrong?
This is the terminal after build:
Successfully built 5d5356e2ca72
Successfully tagged test3:latest
$GOPATH/go.mod exists but should not
But there is no go.mod in the $GOPATH
$ ls -a $GOPATH
. .. bin pkg
This is the go server:
package main
import (
"database/sql"
"flag"
"fmt"
"log"
"net/http"
"strings"
_ "github.com/go-sql-driver/mysql"
)
type FileSystem struct {
fs http.FileSystem
}
var listen = flag.String("listen", ":8989", "listen address")
var dir = flag.String("dir", ".", "directory to serve")
func main() {
db()
flag.Parse()
directory := "./"
fileServer := http.FileServer(FileSystem{http.Dir(directory)})
http.Handle("/", fileServer)
fmt.Printf("Web server running. Listening on %q", *listen)
err := http.ListenAndServe(*listen, http.FileServer(http.Dir(*dir)))
fmt.Printf("%v\n", err)
}
func (fs FileSystem) Open(path string) (http.File, error) {
f, err := fs.fs.Open(path)
if err != nil {
return nil, err
}
s, err := f.Stat()
if s.IsDir() {
index := strings.TrimSuffix(path, "/") + "/index.html"
if _, err := fs.fs.Open(index); err != nil {
return nil, err
}
}
return f, nil
}
func db() {
db, err := sql.Open("mysql", "root:root#tcp(192.168.0.33:4200)/mysql")
if err != nil {
log.Print(err.Error())
} else {
log.Print("DB connected successfully")
}
defer db.Close()
}
This is my go.mod
module test3
go 1.14
require github.com/go-sql-driver/mysql v1.5.0
This is the Dockerfile
FROM golang:alpine AS builder
ENV GO111MODULE=auto \
CGO_ENABLED=0 \
GOOS=linux \
GOARCH=amd64
COPY . .
COPY ./server.go .
COPY ./favicon.ico .
COPY ./assets /assets
EXPOSE 8989
CMD ["go", "run", "./server.go"]
And this is how I build the container:
docker rmi test3 -f
docker build --no-cache -t test3 .
docker run -p 8989:8989 test3

Answer 1

$GOPATH/go.mod exists but should not
By default the goland:alpine image starts the working directory in the GOPATH (i.e. /go) folder where globally installed packages are created with the go install command.
The folder structure looks like:
go/
bin/
src/
pkg/
By directly copying go.mod into the working directory (i.e. GOPATH, i.e. /go), the golang toolkit throws an error, because go.mod is supposed to be in a package folder.
Before the release of Go modules in version 1.11, the convention was to create your packages in the /go/src folder. However, with the release of Go modules you can create golang packages anywhere as long as they include a go.mod file.
So to fix the error, you could copy the golang files (go.mod, etc) into a folder under /home/app or /go/src/app.
Copy into /home/app
RUN mkdir ../home/app
WORKDIR /../home/app
COPY . .
Copy into /go/src/app
RUN mkdir src/app
WORKDIR /src/app
COPY . .