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Michael Di Prisco
Michael Di Prisco

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Dependencies - The Twelve Factor App Methodology

Explicitly declare and isolate dependencies

Welcome back to our exploration of the Twelve Factors in Software Development. Factor 2, Dependencies, is a key element in building robust and portable applications. Let's dive into the world of managing dependencies and understand why it's crucial for your project's success.

Dependencies: Embrace Isolation and Reproducibility

Dependencies refer to external libraries, frameworks, or tools that your application relies on to function correctly. The goal of managing dependencies is to ensure consistent and reproducible builds across different environments.

Why It Matters

Imagine your application relies on a specific version of a library. Without proper dependency management, different developers or deployment environments might end up using different versions. This can lead to compatibility issues, bugs, and headaches during deployment. By managing dependencies effectively, you create a predictable and reproducible environment.

How to Implement

Use a package manager to declare and isolate dependencies. Popular package managers include npm for Node.js, pip for Python, and Maven for Java. Here's a simple example using npm:

# Initialize a new Node.js project
npm init -y

# Install a dependency and save it to the package.json file
npm install express --save
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This ensures that anyone else working on the project or deploying it knows exactly which dependencies are required.

Example in Action

Let's say you're building a web application using a specific version of a JavaScript framework. Instead of manually downloading and including the framework in your project, declare it as a dependency in your package.json file. This way, anyone cloning your project can simply run npm install to get the exact dependencies your application needs.

By following this approach, you minimize the chances of "it works on my machine" issues and create a more reliable development and deployment process.

In our next segment, we'll unravel Factor 3: Config, exploring the significance of storing configuration in the environment and how it contributes to a more adaptable and portable application. Stay tuned!

A word about system tools

Twelve-factor apps also do not rely on the implicit existence of any system tools. Examples include shelling out to ImageMagick or curl. While these tools may exist on many or even most systems, there is no guarantee that they will exist on all systems where the app may run in the future, or whether the version found on a future system will be compatible with the app. If the app needs to shell out to a system tool, that tool should be vendored into the app.

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