ENV variables not coming through godotenv Docker

Question

I have a web app written in Go, dockerised and using gomod.

I cannot get it to read environment variables.

Upon running docker-compose up always returns "Error getting env, not comming through"

I'm using godotenv to try do this. Below is my implementation. I cannot for the life of me figure out what's going wrong. If anyone can see something I'm missing you'll be saving a life.

The main.go, .env, docker-compose.yml and Dockerfile are all in the root of the project

main.go

func main() {
    router := mux.NewRouter()

    err := godotenv.Load()
    if err != nil {
        log.Fatalf("Error getting env, not comming through %v", err)
    } else {
        fmt.Println("We are getting the env values")
    }

    fmt.Println(os.Getenv("MY_ENV"))

}

.env

MY_ENV=thisismyenvvariable
DB_HOST=testdata123
DB_DRIVER=testdata123
DB_USER="testdata123"
DB_PASSWORD=testdata123
DB_NAME=testdata123
DB_PORT=5432

docker-compose.yml

version: '3'
services:
  app:
    container_name: template_123
    build: .
    ports: 
      - 8080:8080 
    restart: on-failure
    volumes:
      - api:/usr/src/app/
    env_file:
      - .env
    depends_on:
      - template-postgres          
    networks:
      - template


  template-postgres:
    image: postgres:latest
    container_name: startup_template_golang_db_postgres
    environment:
      - POSTGRES_USER=${DB_USER}  
      - POSTGRES_PASSWORD=${DB_PASSWORD}
      - POSTGRES_DB=${DB_NAME}
      - DATABASE_HOST=${DB_HOST} 
    ports:
      - '5432:5432'
    volumes:
      - database_postgres:/var/lib/postgresql/data
    env_file:
      - .env
    networks:
      - template
    
  pgadmin:
    image: dpage/pgadmin4
    container_name: pgadmin_container
    environment:
      PGADMIN_DEFAULT_EMAIL: ${PGADMIN_DEFAULT_EMAIL}
      PGADMIN_DEFAULT_PASSWORD: ${PGADMIN_DEFAULT_PASSWORD}
    depends_on:
      - template-postgres
    ports:
      - "5050:80"
    networks:
      - template
    restart: unless-stopped

volumes:
  api:
  database_postgres:                  

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

Dockerfile

# Start from golang base image
FROM golang:alpine as builder

# ENV GO111MODULE=on

# Add Maintainer info
LABEL maintainer="satoshi123"

# 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"]

Answer 1

If you're already using env_file in your docker_compose.yml, you don't really need godotenv, as the environment is already passed down from docker-compose:

version: '3'

services:
    app:
        image: busybox:latest
        command: sh -c 'echo "Hello $$USER!"'
        env_file:
            - .env

# .env
USER=user1

$ docker-compose up
Recreating test_app_1 ... done
Attaching to test_app_1
app_1  | Hello user1!
test_app_1 exited with code 0

This is a better idea than trying to copy the .env file into the container, because it means you can pass environment variables without having to rebuild the container each time ;)

If you nonetheless want to use godotenv, I found that by simply uncommenting the COPY --from=builder /app/.env . line from your Dockerfile, the .env file gets loaded correctly (as godotenv finds it in the directory, whereas if it were commented it wouldn't).

$ docker-compose up
Starting template_123 ... done
Attaching to template_123
template_123 | We are getting the env values
template_123 | thisismyenvvariable
template_123 exited with code 0

If you want to keep it in sync with your filesystem, you will need to use a volume to link your .env with the one on your filesystem, or as I've said, ditch godotenv altogether as it is not really useful in your case.