1## Introduction
2
3Docker is a powerful tool for automating the deployment of applications inside lightweight, portable containers. One of the core components of Docker is the `Dockerfile`, a script that contains a series of commands and instructions to build a Docker image. This article delves into using conditional statements akin to `if-else` in `Dockerfile` scripts with external arguments, offering the flexibility to adjust behavior based on environment variables.
4
5## Understanding Dockerfile Basics
6
7A `Dockerfile` is essentially a script composed of various instructions that guide Docker on how to assemble a specific image. These instructions include `FROM`, `COPY`, `RUN`, `CMD`, and others. While Dockerfiles don't support traditional programming control flow statements like `if-else`, they can achieve conditional logic through a combination of shell commands and external arguments.
8
9## Conditional Logic with IF-ELSE
10
11In a `Dockerfile`, you can simulate `if-else` logic using shell commands. This requires leveraging `RUN` instructions along with Unix shell constructs. A common approach is to evaluate environment variables passed as build arguments or through environment variables.
12
13### Example Dockerfile with Conditional Logic
14
15Let's consider an example where the behavior of the Dockerfile depends on an external argument `BUILD_ENV` which could be either `development` or `production`.
16
17```dockerfile
18# Use an official base image
19FROM ubuntu:20.04
20
21# Define ARG and ENV variables
22ARG BUILD_ENV
23ENV APP_HOME=/app
24
25# Set work directory
26WORKDIR $APP_HOME
27
28# Copy source code to the container
29COPY . .
30
31# Conditional Logic via Shell
32RUN if [ "$BUILD_ENV" = "production" ]; then \
33      echo "Building for production environment"; \
34      apt-get update && apt-get install -y nginx; \
35    else \
36      echo "Building for development environment"; \
37      apt-get update && apt-get install -y curl; \
38    fi
39
40# Expose necessary ports
41EXPOSE 80
42
43# Command to run on container start
44CMD ["nginx", "-g", "daemon off;"]

docker build --build-arg BUILD_ENV=production -t myapp:latest .

1version: '3.8'
2services:
3  web:
4    build:
5      context: .
6      args:
7        BUILD_ENV: "development"