Elixir is great at handling high load, but if you have an existing system and know exactly when the load is going to happen is there a reason not to avoid the re-work and instead scale up the existing PHP application before the event happens? I would dramatically increase the size of the database instance and horizonally scale the PHP application the day before and scale them back down the day after.
This will cost a little money but it’ll save huge amounts of developer time compared to a rewrite, and develoer time is far more expensive than servers.
Thank you. I really appreciate the honesty of saying elixir would be great, but I can still save the day with current technology. Fair answer! Even though massive scaling would be required, it’s still just 2 days every year, and thus probably cheaper even in medium- to long-term