The Problem with CORS in Monorepo Applications

Oct 13, 2025 by magicalceylontours.com 77 views

Introduction

In this article, we will delve into the issue of CORS (Cross-Origin Resource Sharing) errors that can occur when deploying a monorepo application using Railway. A monorepo is a single repository that contains multiple projects or services, which can be beneficial for managing complex applications. However, when deploying these services, CORS errors can arise, hindering the functionality of the application.

What is CORS?

CORS is a security feature implemented in web browsers to prevent web pages from making requests to a different domain than the one the web page was loaded from. This is done to prevent malicious scripts from making unauthorized requests on behalf of the user. However, when developing and testing applications, CORS can become a hindrance, especially when working with services that need to communicate with each other.

The Problem with CORS in Monorepo Applications

When deploying a monorepo application using Railway, CORS errors can occur when trying to access services from different origins. This is because the default configuration of Railway does not include the necessary CORS headers in the response. As a result, the browser blocks the request, and the application fails to function as expected.

The Go Server and CORS

In the case of the Go server, the issue is not with the server itself, but rather with the configuration of Railway. The Go server correctly processes the request, but the response does not include the necessary CORS headers. This is why the browser blocks the request, and the application fails to function.

Solving the CORS Error

To solve the CORS error, we need to configure Railway to include the necessary CORS headers in the response. This can be done by adding a middleware to the Go server that sets the CORS headers. Here is an example of how to do this:

package main

import (
	"fmt"
	"log"
	"net/http"

	"github.com/gorilla/mux"
)

func main() {
	r := mux.NewRouter()

	r.HandleFunc("/sse", func(w http.ResponseWriter, r *http.Request) {
		// Process the request
		fmt.Fprint(w, "Hello, World!")
	}).Methods("GET")

	// Set CORS headers
	r.Use(func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			w.Header().Set("Access-Control-Allow-Origin", "*")
			w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
			w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Accept, Authorization")
			next.ServeHTTP(w, r)
		})
	})

	log.Fatal(http.ListenAndServe(":8080", r))
}

In this example, we use the Gorilla MUX router to set up a handler for the /sse endpoint. We then use a middleware to set the CORS headers in the response. The Access-Control-Allow-Origin header is set to *, which allows requests from any origin. The Access-Control-Allow-Methods header is set to GET, POST, PUT, DELETE, OPTIONS, which allows the browser to make requests using these methods. The Access-Control-Allow-Headers header is set to Content-Type, Accept, Authorization, which allows the browser to include these headers in the request.

Conclusion

In conclusion, CORS errors can occur when deploying a monorepo application using Railway. However, by configuring the Go server to include the necessary CORS headers in the response, we can solve the CORS error and ensure that the application functions as expected. By following the steps outlined in this article, you can configure your Go server to include the necessary CORS headers and avoid the CORS error.

Additional Resources

Troubleshooting CORS Errors

If you are still experiencing CORS errors after configuring your Go server to include the necessary CORS headers, there are a few things you can try to troubleshoot the issue:

Check the browser console for any error messages related to CORS.
Verify that the CORS headers are being included in the response by checking the response headers in the browser console.
Check the Railway configuration to ensure that the CORS headers are being included in the response.
Try accessing the service from a different origin to see if the CORS error occurs.

Introduction

In our previous article, we discussed the issue of CORS (Cross-Origin Resource Sharing) errors that can occur when deploying a monorepo application using Railway. We also provided a solution to the problem by configuring the Go server to include the necessary CORS headers in the response. In this article, we will answer some frequently asked questions related to CORS errors in monorepo applications.

Q: What is CORS, and why is it a problem in monorepo applications?

A: CORS is a security feature implemented in web browsers to prevent web pages from making requests to a different domain than the one the web page was loaded from. This is done to prevent malicious scripts from making unauthorized requests on behalf of the user. In monorepo applications, CORS can become a problem when services need to communicate with each other, and the browser blocks the request due to the lack of CORS headers in the response.

Q: Why do I need to configure CORS headers in my Go server?

A: You need to configure CORS headers in your Go server because the default configuration of Railway does not include the necessary CORS headers in the response. By including the CORS headers in the response, you can allow the browser to make requests to your service from a different origin.

Q: What are the different types of CORS headers, and how do I set them?

A: There are several types of CORS headers that you can set in your Go server. These include:

Access-Control-Allow-Origin: This header specifies the allowed origins for the request. You can set it to * to allow requests from any origin.
Access-Control-Allow-Methods: This header specifies the allowed methods for the request. You can set it to GET, POST, PUT, DELETE, OPTIONS to allow the browser to make requests using these methods.
Access-Control-Allow-Headers: This header specifies the allowed headers for the request. You can set it to Content-Type, Accept, Authorization to allow the browser to include these headers in the request.

Here is an example of how to set these headers in your Go server:

package main

import (
	"fmt"
	"log"
	"net/http"

	"github.com/gorilla/mux"
)

func main() {
	r := mux.NewRouter()

	r.HandleFunc("/sse", func(w http.ResponseWriter, r *http.Request) {
		// Process the request
		fmt.Fprint(w, "Hello, World!")
	}).Methods("GET")

	// Set CORS headers
	r.Use(func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			w.Header().Set("Access-Control-Allow-Origin", "*")
			w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
			w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Accept, Authorization")
			next.ServeHTTP(w, r)
		})
	})

	log.Fatal(http.ListenAndServe(":8080", r))
}

Q: How do I troubleshoot CORS errors in my monorepo application?

A: To troubleshoot CORS errors in your monorepo application, you can follow these steps:

Check the browser console for any error messages related to CORS.
Verify that the CORS headers are being included in the response by checking the response headers in the browser console.
Check the Railway configuration to ensure that the CORS headers are being included in the response.
Try accessing the service from a different origin to see if the CORS error occurs.

Q: Can I use a different approach to solve CORS errors in my monorepo application?

A: Yes, you can use a different approach to solve CORS errors in your monorepo application. One approach is to use a proxy server to forward requests from the browser to your service. This can help to avoid CORS errors by allowing the browser to make requests to the proxy server, which can then forward the request to your service.

Conclusion

In conclusion, CORS errors can occur when deploying a monorepo application using Railway. However, by configuring the Go server to include the necessary CORS headers in the response, you can solve the CORS error and ensure that your application functions as expected. By following the steps outlined in this article, you can troubleshoot CORS errors and ensure that your monorepo application is working correctly.