Configure HAProxy to Accept Preflight Requests
Recently I developed an API with Spring Boot. All the tests on the local environment went well with Postman. However, when deploying to prod through HAProxy, I got this error:
There are also other errors regarding missing headers, origin…
There are some solutions available, such as add code to my Spring Boot code base. I don’t like this method since it’s not pure.
Why adding non-business code in API.
That’s why I need to find another solution.
It turned out, the solution is simple.
First, add a new backend only for serving CORS in HAProxy:
backend cors_backend http-after-response set-header Access-Control-Allow-Origin "*" http-after-response set-header Access-Control-Allow-Headers "*" http-after-response set-header Access-Control-Max-Age "31536000" http-request return status 200
Now, in the frontend part, add a check for OPTIONS request and direct that request to this backend:
frontend your_fe ... acl is_options method OPTIONS ... use_backend cors_backend if is_options # put your actual backend below this
Of course, in your actual backend, you need to set the CORS headers:
backend your_main_backend ... # START CORS http-response add-header Access-Control-Allow-Origin "*" http-response add-header Access-Control-Allow-Headers "*" http-response add-header Access-Control-Max-Age 3600 http-response add-header Access-Control-Allow-Methods "GET, DELETE, OPTIONS, POST, PUT, PATCH" # END CORS server w1 server:8080
And that’s all you need. Now you can work with your API CORS-free