Routing Part of an Application to a New Version with HAProxy

Sometimes you need to roll out only part of an application to production. This often happens after refactoring or when introducing a new version of specific endpoints. With HAProxy you can route only selected requests to the new backend while keeping the rest of the traffic on the existing servers.

This approach makes it easy to test changes in production without switching the entire application at once.

Haproxy configuration

listen frontend_http
  bind *:80
  bind *:443 ssl crt /etc/haproxy/crt/ssl.pem
  mode http

  acl is_legacy_paths path_reg -i ^/(api|api_v1|v1).*
  acl is_legacy_method url_reg -i .*method=notify.*
  use_backend backend_new if is_legacy_paths is_legacy_method

  default_backend backend_main

Backend setup

In the end you need two backends: the default one (backend_main) with the old server pool, and a second backend (backend_new) with the new servers.

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