Thoughts on the raspberry pi 4 + 10k TCP connections with Vert.x

Background Context

I recently picked up a Raspberry Pi 4 [4GB edition]. I had been debating picking up a Linux system for some dev work. I don’t like using Docker right from the get go as a dev environment. My general workflow for any project goes in the following steps - for a Kotlin project

  1. Run from IDE
  2. Run from terminal via build tool such as maven or bazel
  3. Compile to a fat jar and run using java -jar <project>.jar
  4. Run fat jar on a Linux server [now possible]
  5. Run as a docker container
  6. Run as a Kubernetes deployment

I know many devs have jumped directly to step 5 but I think it is still important to make sure that steps 1-4 are compiling and running properly. Step 1 is still important because other devs, who do not have context, will navigate to your project [in their IDE] to add new features or fix bugs. Very likely, they will add a bunch of print statements in the project and start making requests to see what the internals look like. I guess you could use the documentation on confluence but sometimes it is easier and faster to just log-dump the request. They should to be able to spin the service up easily when they have no context. The project should not fail to startup because a required environment variable was not set - set a sane default, log the behaviour [such as persistence disabled] and proceed.

If for any reason you think this is a lot of work - I present you Margaret Hamilton the lead developer on the Apollo mission standing next to the hard copy of the code base.

VPS vs Raspberry Pi

I was thinking of getting a digital ocean VPS - with the 1CPU 1GB ram costing about $5/month or $20 for the 2CPU 4GB ram. The monthly cost was definitely a factor since I was planning on running multiple things 24/7 and not just one small app. The advantage was being able to easily expose it on the internet for demo reasons. For an in house server, I would have to port forward on my router, which I was [and still am] not a big fan of. Ngrok [] definitely could be a quick workaround. Another concern was that I love doing benchmarks and load testing. I did not want to cause any DDoS triggers on DO’s end getting my account suspended or anything like that.

I picked up the CanaKit Raspberry Pi 4 Starter Kit (4GB RAM) from Amazon. Definitely a bit more expensive than I thought it was going to be all things considered. It was relatively easy to set up the heat sinks and the case. Hooked it up to a keyboard, mouse, and my TV to install the OS. I don’t need a GUI so I installed the headless Raspberry Pi OS which is debian based [apt - not yum]. raspberrypi.local is set up to connect to the Pi.

pi@raspberrypi ➜  ~ uname -a
Linux raspberrypi 4.19.118-v7l+ #1311 SMP Mon Apr 27 14:26:42 BST 2020 armv7l GNU/Linux

What’s running on it?

A server is useless if it is not running anything. I had a few things I knew I was going to set up. The first was a DNS level ad blocker pi hole []. Gave my Pi a static IP via DHCP reservation in my Rogers router and set up pi hole to block out any ads for all devices that used it as a DNS Server. Just this one application alone made the pi worth it. Pi hole helps quite a bit. Doesn’t block everything [like ads on YouTube in mobile] but it is good enough. Also caches the DNS responses so browsing seems a bit zippier too. It is PHP based so it needs a webserver to call out to the php scripts - lighthttpd in this case. Not a big fan of this. Why are we still using PHP + web servers in 2020??

List of other things I set up not including things like zsh and htop:

  1. OpenJDK [OpenJ9 seems to have limited to no support for ARM]
  2. Redis
  3. Postgres
  4. Grafana
  5. Prometheus
  6. MongoDB
  7. InfluxDB [docker container]
  8. Docker registry [docker container]
  9. Node.js for Vue.js dev work
  10. Caddy
  11. Nginx [inactive]
  12. rustc and go

I set up gitea [ ] which is a self hosted git server as well - but the SSH permissions to push/pull got borked :(

I installed caddy as a reverse proxy for the pi to route to various services I have running behind it. Caddy is similar to nginx but with slightly easier configurations and automatic HTTPS setup.

# Caddyfile
localhost, raspberrypi.local {
route / {
respond "{} {system.os} {system.arch} {http.request.proto} {http.request.method} {http.request.uri}"
➜  ~ curl -k https://raspberrypi.local/
05/Jul/2020:15:17:16 -0400 linux arm HTTP/2.0 GET /

Load testing and 10k connections

Running wrk on Caddy [with logging turned on] I got the following results

$ wrk -t 32 -c 64 -d20s https://raspberrypi.local/
Running 20s test @ https://raspberrypi.local/
32 threads and 64 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 7.15ms 3.91ms 60.06ms 83.81%
Req/Sec 291.33 36.82 390.00 74.65%
185508 requests in 20.07s, 25.12MB read
Requests/sec: 9241.25
Transfer/sec: 1.25MB

Next I setup a Vert.x TCP server and used tcpkali [ ] to see if the Pi could handle 10k concurrent connections.

As always, I opted to use vert.x to create the tcp server. A tcp server in vert.x can be spun up very easily with the following lines of code

val vertx = Vertx.vertx()

vertx.createNetServer().connectHandler {
// handle connection
it.handler {
// handler socket data

I also added some prometheus metrics:

  1. Node exporter to get the system information of the pi during the load test
  2. Micrometer bindings to get the JVM information
  3. Vert.x metrics to get the net server connection count + a custom packet received counter

The entire main function can be viewed in here -

Then the test began using tcpkali tcpkali -m '$' -r 10 -c 10k -T 240s --connect-rate=1000 <pi-ip>:9091

Some grafana screenshots:

Vert.x net server connections + packet received
Screen Shot 2020-07-04 at 12.48.09 PM.png

CPU usage
Screen Shot 2020-07-04 at 12.47.17 PM.png

JVM memory used - vert.x is really memory efficient
Screen Shot 2020-07-04 at 12.47.05 PM.png

Node exporter quick stats
Screen Shot 2020-07-04 at 12.46.00 PM.png

For a tiny little device it seems more than capable for a single dev. I would not use it as a build server for your company’s production apps but to have an always on linux system available is really nice to have.