Make VERY SURE to outline the runtime’s benefits:

• Preemptive scheduling (what 99% of the runtimes out there don’t have)
• OTP’s let it crash and get restored way of work
• Supervisors!
• Extremely easy to achieve parallelism and concurrency

Most people just fangirl at the language and a lot of other people are very rightfully not impressed. This decision is only 5-10% about the languages (say because of meta-programming / macros and good libraries). 90-95% of the benefit is the runtime so do your very best to highlight that!

Preemptive scheduling

Not one single OTP Process (what in other programming languages are called actors, green threads, fibers) can affect the latency of the others. The average execution time of any given function should remain mostly the same even under heavy load – a huge selling point IMO. That’s why Phoenix apps on $5 worth of servers can handle 2000+ requests a second (while a Ruby on Rails or Laravel vanilla app can be brought to its knees by 100-200 requests a second).

Parallelism / concurrency

Consider this:

def send_email_batch(list_of_emails) do
  # This will receive no more than 100 email addresses
  YourMailSender.send_batch_message(list_of_emails)
end

list_of_emails # Supposedly a very big list
|> Stream.chunk(100)
|> Task.async_stream(&send_email_batch/1, timeout: :infinity, max_concurrency: 20)
|> Stream.run()

This will get a big list of emails, break the list into smaller lists of 100 emails each and send each chunk (batch) in parallel, but it never sends more than 20 batches at the same time (the :max_concurrency option of Task.async_stream), e.g. at any given time maximum of 2000 emails are being sent (if we assume this is your email sending provider’s API rate limit and that you want to comply with it).

This extremely transparent parallelism / concurrency is what brought me to Elixir.

Some great thoughts by Dimi and you might also find what Robert wrote in the Erlang Rationale worth a look

These EF threads might also contain something of use?

Good luck and let us know how you get on