Nixpacks build failure during runtime detection

Build Pipeline Analysis

Railway utilizes Nixpacks as the default build system to automatically analyze source code and generate optimized Docker images. When the analysis phase fails to identify a compatible language runtime or project structure, the deployment process cannot proceed to the rollout phase.

In scenarios where the repository contains a mix of configuration files or non-standard directory structures, the automated detection may fail to determine the correct build plan. This creates a dependency on manual overrides to ensure the container is built with the intended environment.

What are the specific criteria Nixpacks uses to prioritize one runtime over another when multiple indicators are present? In what cases is a manual Dockerfile required to override the automated detection failure?