Handling environment variables in Containers (Docker/Podman)

Environment variables are an essential way to configure your services. They make it easy to configure services for different environments & deployments.

There are several ways to handle environment variables in containers:

1. You can pass them directly to the container at runtime using the -e flag, like this:

$ docker run -e VAR_NAME=value -e VAR_NAME2=value2 image_name

1. You can also set environment variables in the Dockerfile for your image. This can be done using the ENV directive, like this:

ENV VAR_NAME value
ENV VAR_NAME2 value2

1. You can use a .env file to store your environment variables and pass them to the container at runtime using the --env-file flag:

$ docker run --env-file .env image_name

The .env file should contain one VAR_NAME=value pair per line.

POSTGRES_USER=postgres
POSTGRES_PASSWORD=postgres
POSTGRES_PORT=5432
POSTGRES_DB=my-db

1. You can also pass environment variables to a container when using docker-compose. To do this, you can set them in the environment section of the docker-compose.yml file, like this:

version: '3'
services:
web:
    environment:
    - VAR_NAME=value
    - VAR_NAME2=value2
    image: image_name

In Podman, you can use the same flags and methods to handle environment variables.

Takeaway -

A full working example of this article can be found below.