Powerbuilding with Fly

Dj Walker-Morgan

Identifying your build When you deploy, the flyctl application looks for instructions to build the image in a Dockerfile or creates a builder VM to do the image build. Let’s start with the flags that control where flyctl looks for things. -c, –confi

Fly.io

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Dj Walker-Morgan

•4 min read•intermediate•

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•View Original

DockerNGINX

Overview

The article discusses how to effectively build and deploy Docker images using Fly's infrastructure, focusing on the use of the flyctl application and its various configuration options. It highlights the importance of build arguments and environment variables in customizing deployments.

What You'll Learn

1

How to specify custom Dockerfile and configuration file using flyctl

2

Why to use build arguments for customizing Docker image builds

3

When to use Fly Secrets for sensitive data instead of build arguments

Key Questions Answered

How does flyctl determine which Dockerfile to use for building images?

The flyctl application looks for a Dockerfile in the current directory by default, but users can specify a different file using the --dockerfile option. This is particularly useful when managing multiple applications from the same directory.

What are the differences between ARG and ENV in Docker?

The ARG command allows you to define variables that are available only during the build process, while the ENV command sets environment variables that persist in the running container. This distinction is crucial for managing configurations effectively.

When should build arguments not be used in Fly applications?

Build arguments should not be used for passing sensitive information, as they are baked into the Docker image and can be retrieved. Instead, Fly Secrets should be used for securely injecting sensitive data as environment variables during runtime.

Technologies & Tools

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Containerization

Docker

Used for building images that are deployed on Fly's infrastructure.

Platform

Fly

Provides infrastructure for deploying Docker images.

Key Actionable Insights

1
Utilize the --config option in flyctl to manage multiple configurations efficiently.
This is particularly useful for developers working on several applications from a single directory, allowing for better organization and deployment management.

2
Leverage ARG and ENV commands in your Dockerfile to control runtime configurations dynamically.
By setting up these variables, you can easily adjust application settings without modifying the Dockerfile, enhancing flexibility in deployment.

3
Avoid using build arguments for sensitive data; instead, use Fly Secrets for secure data handling.
This ensures that sensitive information is not exposed in the image, maintaining security and compliance for your applications.

Common Pitfalls

1

Using build arguments to pass sensitive data can lead to security vulnerabilities.

Since build arguments are included in the image, they can be accessed by anyone with access to the image. Instead, use Fly Secrets for sensitive information.