The Case of the 50ms request

This repo is a live demo of the puzzle The Case of the 50ms request from wizardzines's mysteries, thus allowing for people to investigate the problem and try to debug it themselves.

Problem

You have a program that uploads very tiny files to a server. You notice in your monitoring that these file uploads are a little slow — maybe about 50ms on average. The uploading code is in Javascript, so you write a tiny Javascript program called slow.js to reproduce the problem so you can easily investigate it. The program prints out the time elapsed for the request in milliseconds.

You have a choice: you can SSH to the client machine (which is making the requests), or the server machine (which is serving the requests).

Getting started

Compose container

Build the docker images and run them

docker-compose up

You will see the logs generated by the containers.

Interactive shell

Run an interactive shell inside either container for investigating

docker exec -it server /bin/sh # For server
docker exec -it client /bin/sh # For client

Notice that the hostname of both containers are server/client respectively.

Server

The server runs a simple HTTP server that listens on port 8000

IMPORTANT: Do not look at the server implementation (server.py) it contains spoilers.

Client

The client is just a simple alpine based image containing a script slow.js that recrates the problem, by posting data to the server and measuring the time it took.

node slow.js

You are allowed to examine this script.

Solution

The solution can be found here.