How to properly deal with .env files in docker

Question

I have a node app using dotenv to keep track of env variables. Its using the .env file in the root folder to get the variables in runtime. The problem is when i'm using docker to build a node image the below line copies the .env file for the build as well

FROM node:latest

# Create app directory
RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app

# Install app dependencies
COPY package.json /usr/src/app/
RUN npm install

# Bundle app source
COPY . /usr/src/app

EXPOSE 8000

If i build & pull the image from dockerhub. The file already contains the .env file i used in development. Ideally , i would like to specify a different .env file for production. (perhaps manually creating a new .env file in the production server)

i tried specifying the .env file in dockerignore . but line COPY . /usr/src/app still seems to copy the env file as well.

I do not need to use dotenv as such. I tried specifying it like the below

version: '2'

services:
  node:
    container_name: node
    build: .
    env_file: .env
    volumes:
      - .:/usr/src/app
      - /usr/src/app/node_modules
    command: npm start

so i really dont need to specify a .env folder in the build. But this doesnt work as well.

How do i stop the COPY command from copying the .env file?

Answer 1

There's a file for that!

Before the docker CLI sends the context to the docker daemon, it looks for a file named .dockerignore in the root directory of the context. If this file exists, the CLI modifies the context to exclude files and directories that match patterns in it. This helps to avoid unnecessarily sending large or sensitive files and directories to the daemon and potentially adding them to images using ADD or COPY.

In your case, you'll just need to echo .env >> .dockerignore while in the same directory as your Dockerfile.

Answer 2

create a .dockerignore file in the same directory as .env and Dockerfile then add .env file to .dockerignore file. now Docker will not include .env file while building the image.

#.dockerignore 
.env