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Docker: "go.mod file not found" when it clearly exists

I'm trying to make a fullstack app that uses a go backend and a nextjs frontend (which I haven't created yet). I was following a tutorial for making the backend and everything was working fine so far. However, I wanted to move the backend stuff into its own folder so I could keep it and the frontend separate. Now, whenever I run docker compose build it completes with no errors, but when I run docker compose up, this is what I get (I'm using air to have hot reload functionality):

goapp-1  | watching .
goapp-1  | watching backend
goapp-1  | watching backend/cmd
goapp-1  | watching backend/cmd/database
goapp-1  | watching backend/cmd/handlers
goapp-1  | watching backend/cmd/models
goapp-1  | watching backend/tmp
goapp-1  | !exclude tmp
goapp-1  | building...
goapp-1  | go: go.mod file not found in current directory or any parent directory; see 'go help modules'
goapp-1  | failed to build, error: exit status 1

However, when I go into Docker desktop and run ls in that image, it shows that go.mod is right there!

enter image description here

So what's the issue?

I've tried changing the target directories and contexts in compose.yaml and my dockerfile, all to no success. Running go build instead of air gives me the same error as well.

Here's my file tree:

databeis2
 ┣ .vscode
 ┃ ┗ settings.json
 ┣ backend
 ┃ ┣ cmd
 ┃ ┃ ┣ ...
 ┃ ┃ ┣ main.go
 ┃ ┃ ┗ routes.go
 ┃ ┣ tmp
 ┃ ┃ ┣ build-errors.log
 ┃ ┃ ┗ main
 ┃ ┣ .air.toml
 ┃ ┣ Dockerfile
 ┃ ┣ go.mod
 ┃ ┣ go.sum
 ┃ ┗ pre_cmd.txt
 ┣ tmp
 ┃ ┗ build-errors.log
 ┣ .env
 ┗ compose.yaml

My dockerfile:

FROM golang:1.21

WORKDIR /app

RUN go install github.com/cosmtrek/air@latest

COPY . .
RUN go mod tidy

And compose.yaml:

services:
  goapp:
    build:
      context: ./backend
    env_file:
      - .env
    ports:
      - 8000:8000
    volumes:
      - .:/app
    command: air ./cmd/main.go -b 0.0.0.0
    depends_on:
      - db

  db:
    image: postgres:alpine
    environment:
      - POSTGRES_USER=${DB_USER}
      - POSTGRES_PASSWORD=${DB_PASSWORD}
      - POSTGRES_DB=${DB_NAME}
    ports:
      - 5432:5432
    volumes:
      - postgres-db:/var/lib/postgresql/data

volumes:
  postgres-db:

Any help would be massively appreciated!!

Solution

  • I solved it! The issue was I needed to change my WORKDIR to backend after copying the files in my dockerfile.

    FROM golang:1.21

WORKDIR /app

RUN go install github.com/cosmtrek/air@latest

COPY . .
# Add the below line 
WORKDIR /app/backend

RUN go mod tidy