How can I increase max concurrent request of Phoenix on fly.io?

nallwhy · June 24, 2022, 12:05pm

I made a toy project that provides a simple API for testing.

This project is served via fly.io.
Here is my fly.io configuration below. I configured services.concurrency.hard_limit to 10000.

github.com

nallwhy/json_corp/blob/main/fly.toml

# fly.toml file generated for json-corp on 2022-06-03T02:31:32+09:00

app = "json-corp"

kill_signal = "SIGINT"
kill_timeout = 5
processes = []

[build]
  builder = "heroku/buildpacks:20"
  buildpacks = ["https://cnb-shim.herokuapp.com/v1/hashnuke/elixir"]

[env]
  PORT = "8080"

[experimental]
  allowed_public_ports = []
  auto_rollback = true

[[services]]

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I wanted to do a load test for this project. Below is the code I used for the load test.

github.com

nallwhy/test_api/blob/main/notebooks/load_test.livemd

# Load Test

```elixir
Mix.install([:chaperon, :req])
```

## Section

<!-- livebook:{"branch_parent_index":0} -->

## With Req

```elixir
require Logger

count = 500
timeout = 2

url = "https://json.media/test_api/api?timeout=#{timeout}"
# url = "http://localhost:4000/test_api/api?timeout=#{timeout}"

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When I run the code that tests with req, about 200 requests returns ok and other requests returns error %Mint.TransportError{reason: :closed}.

How can I increase max concurrent request of Phoenix on fly.io?

LostKobrakai · June 24, 2022, 12:09pm

Are you sure it’s the currency limit you run into and not the instance(s) being overwhelmed?

msimonborg · June 24, 2022, 12:11pm

There was a discussion about this on the fly.io community forum a few days ago max concurrency can not be greater than 300 - #4 by fxsjy - Fly.io

I think that the issue is exactly what you’re experiencing here, and was answered by the fly team.