The Silent Deployment Killer: File Path Case Sensitivity
If you've ever encountered mysterious TypeScript import errors when deploying your Node.js application to Heroku that weren't present in your local development environment, you might have fallen victim to one of the most common yet elusive issues in cross-platform development: file path case sensitivity.
In this post, I'll walk through a real-world example of this problem and provide a systematic approach to identifying and fixing these issues.
The Problem
Recently, while deploying our NestJS application to Heroku, we encountered the following error:
src/modules/move-in-requests/dto/update-move-in-request.dto.ts:4:40 - error TS2307: Cannot find module './create-move-in-request.dto' or its corresponding type declarations.
4 import { CreateMoveInRequestDto } from './create-move-in-request.dto'
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The frustrating part? Everything worked perfectly in our local development environment. The imports were resolving correctly, TypeScript was happy, and the application ran without issues.
Understanding the Root Cause
This problem stems from a fundamental difference between operating systems:
- macOS and Windows (by default) use case-insensitive filesystems
- Linux (including Heroku's dynos) uses a case-sensitive filesystem
This means that on macOS, the files create-move-in-request.dto.ts and create-move-In-request.dto.ts are treated as the same file. However, on Linux, these are considered completely different files.
Diagnosing the Issue
When you encounter TypeScript import errors during deployment that don't appear locally, follow these steps to diagnose the problem:
Check the exact error message: Look for "Cannot find module" errors with specific file paths.
Examine the actual filenames in your repository: Use Git commands to see how files are tracked:
git ls-files path/to/directory
-
Compare with your local filesystem: Use
ls -lato see the actual files on your system:
ls -la path/to/directory
In our case, we discovered that Git was tracking the file as create-move-In-request.dto.ts (with a capital 'I'), but our imports were looking for create-move-in-request.dto.ts (with a lowercase 'i').
The Solution
Once you've identified a case sensitivity mismatch, here's how to fix it:
- Remove the file from Git's index (but keep it on your filesystem):
git rm --cached path/to/file-with-Wrong-Case.ts
- Add the file back with the correct case:
git add path/to/file-with-correct-case.ts
- Commit the change:
git commit -m "fix: correct case sensitivity in filename"
- Push to your remote repository:
git push origin your-branch
- Redeploy your application
Preventing Future Issues
To avoid similar problems in the future, consider implementing these best practices:
Use consistent naming conventions: Stick to kebab-case for filenames in NestJS projects.
Configure Git to be case-sensitive:
git config core.ignorecase false
Use a linter rule to enforce consistent filename casing.
Consider using Docker for development to match your production environment.
Add a pre-commit hook to check for case inconsistencies.
Use continuous integration to build your application in a Linux environment before deployment.
Conclusion
File path case sensitivity issues can be frustrating to debug, especially when they only appear in production. By understanding the root cause and following a systematic approach to diagnosis and resolution, you can quickly fix these issues and prevent them from recurring.
Remember that these problems are particularly common when developing on macOS or Windows and deploying to Linux-based environments like Heroku, AWS, or Docker containers.
Have you encountered similar issues in your deployments? Share your experiences and solutions in the comments below!
This post is part of our "Debugging in Production" series, where we share real-world solutions to common deployment issues.
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