Moin! 🖖 My name is Sebastian.
I create Open-Source Software and I write about it. I am Serverless Expert and GraphQL Specialist, Recreational Photographer, AI Enthusiast, and former AWS Serverless Hero. I do Serious Cloud Computing in Hamburg, Germany
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keffeine: Learning Journey of building an iOS App with AI
I’ve been tinkering on a project that’s been both challenging and rewarding: building a native iOS app in Swift to control my KEF speakers. It started with a simple need — a clearer view of what’s playing — but quickly turned into a deep dive into debugging, APIs, and SwiftUI. Here I’ll share what I learned and the moments that made it worthwhile.
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Deploy Serverless Containers to Scaleway with OpenTofu
After building multiarch Docker containers for Rust applications, you want to deploy them somewhere. Scaleway’s serverless container platform offers a straightforward way to run containers without managing infrastructure, and OpenTofu provides the infrastructure-as-code tooling. This guide walks through deploying Docker containers to Scaleway using the OpenTofu provider, from setting up the registry to running your container.
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Multiarch Docker Containers with Rust
This guide shows how to build multiarch Docker containers for Rust applications using
cargo zigbuildfor cross-compilation and Docker build commands for architecture-specific or multiarch container images. Based on the example for Building a Rust API with Rocket and JWT Authentication, this guide provides the next steps. -
Building a Rust API with Rocket and JWT Authentication
When building backend APIs, JWT authentication is a common requirement. In Rust, you’ve got several web frameworks to choose from, and Rocket is one that makes request handling feel natural with its request guard system. Combining Rocket with JWTiny for JWT validation and JWKServe as a local identity provider gives you a complete setup for development and testing without external dependencies.
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JWTiny: Minimal JWT Validation for Rust
I was learning Rust with an example project that needed JWT validation. The popular
jsonwebtokencrate depends onserde, but I wantedminiserdeinstead. That constraint led me to build my own validator — handling signature verification, claims validation, and remote key fetching, designed for reuse across requests. JWTiny is the result. -
JWKServe: A Fake JWT Authentication Service for Local Development
When writing backend services that validate JWT access tokens, you run into a frustrating problem: you need a real identity provider just to test your authentication logic. With Cognito, Auth0, or other OpenID Connect providers, spinning up an authentication service for local development or CI pipelines adds unnecessary complexity. You need valid signatures and correct claims, not the provider itself. That’s where JWKServe comes in.
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Static Website Hosting in Europe with Free Services
The AWS European Sovereign Cloud is maybe the most interesting developments of the current cloud computing era; having AWS create a dedicated branch for european workloads is the next big move. But, how do you run a static website without using US vendors at all?
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AWS CDK: Serverless WebService Blueprints
The past days have been full of content about serverless workloads with AWS AppSync, Amazon Cognito, and AWS Fargate. This guide wraps up all scenarios and is your starting point if you want to build modern serverless applications with AWS using the Cloud Development Kit (CDK).
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AWS CDK: AppSync Events API with Cognito for WebSockets and React
The Amazon AppSync Events API was recently announced and is a new feature to use a WebSocket API for real-time communication. Based on the Amazon Cognito User Pool with Managed Login and guide for GraphQL Data API in Amazon AppSync, this guide shows you how to add real-time communication to your React application using WebSockets and the Amazon AppSync Events API with Amazon Cognito.
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AWS CDK: AppSync GraphQL API with Cognito and Apollo Client in React
The Amazon Cognito User Pool with Managed Login is a great baseline to start a new project. This guide adds an AWS AppSync GraphQL Data API to the project and shows you how to use the Amazon Cognito Access Token to authenticate against the GraphQL API using the Apollo Client in React.
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AWS CDK: Cognito Managed Login with Custom Domain
Just before AWS re:Invent 2024, Amazon Cognito released a new feature called Managed Login. Using this, Amazon Cognito will provide the fully-managed, hosted sign-in and sign-up experience for your users. This guide will show you how to configure an Amazon Cognito User Pool with a custom domain and Managed Login; all done with the AWS Cloud Development Kit (CDK).
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Cursor: Rules for AI Code Editor
The Cursor AI Code Editor is my default editor these days for writing code. As with other code companions, Cursor offers a chat-like interface to interact with your codebase and their AI services. More important, Cursor supports project-specific customizations; using a file in your project root.
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