Nginx Troubleshooting Scenarios

Scenario: "Fukuoka": Forbidden Association

Level: Easy

Type: Fix

Access: Paid

Description: There's a web server running on this host but curl localhost returns the default 404 Not Found page.

Fix the issue so that a file is served correctly and the message Welcome to the Real Site! is returned.

Test: Running curl localhost should return HTTP 200 with the message Welcome to the Real Site!.

The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.

Time to Solve: 15 minutes.

Scenario: "Cape Town": Borked Nginx

Level: Medium

Type: Fix

Access: Email

Description: There's an Nginx web server installed and managed by systemd. Running curl -I 127.0.0.1:80 returns curl: (7) Failed to connect to localhost port 80: Connection refused , fix it so when you curl you get the default Nginx page.

Test: curl -Is 127.0.0.1:80|head -1 returns HTTP/1.1 200 OK

Time to Solve: 15 minutes.

Scenario: "Melbourne": WSGI with Gunicorn

Level: Medium

Type: Fix

Access: Paid

Description: There is a Python WSGI web application file at /home/admin/wsgi.py , the purpose of which is to serve the string "Hello, world!". This file is served by a Gunicorn server which is fronted by an nginx server (both servers managed by systemd). So the flow of an HTTP request is: Web Client (curl) -> Nginx -> Gunicorn -> wsgi.py . The objective is to be able to curl the localhost (on default port :80) and get back "Hello, world!", using the current setup.

Test: curl -s http://localhost returns Hello, world! (serving the wsgi.py file via Gunicorn and Nginx)

Time to Solve: 20 minutes.

Scenario: "Depok": Nginx with Brotli

Level: Medium

Type: Fix

Access: Paid

Description: You are tasked to add compression to the company website. The website is running on an Nginx server, and you decide to add Brotli compression to it.

Brotli has became very popular these days because of its high compression ratio. It's a generic-purpose lossless compression algorithm that compresses data using a combination of a modern variant of the LZ77 algorithm, Huffman coding, and 2nd order context modeling.

For this purpose, you decided to compile the brotli modules yourself and add them to the Nginx server.

The location of the Brotli source code is at /home/admin/ngx_brotli. The nginx source code (needed to compile the modules) is located at /home/admin/nginx-1.18.0. From the ngx_brotli repository first you need to compile the brotli dependencies and then configure and make modules for Nginx. Afer that you need to add the modules to the Nginx configuration.

After installing the modules, you need to make sure the responses from the server are being served with compression.

Create a port-forward to port 80 from the server to your computer and check the header Content-Encoding, responses must return br for Brotli compression. You can also use curl -H "Accept-Encoding: br, gzip" -I http://localhost to check the header.

Something nice about Brotli is that it fails over to gzip if the client doesn't support Brotli, so curl -H "Accept-Encoding: gzip" -I http://localhost should return gzip instead.

Test: curl -H "Accept-Encoding: br" -sI http://localhost returns the header Content-Encoding: br.

The "Check My Solution" button runs the script _/home/admin/agent/check.sh_, which you can see and execute.

Time to Solve: 15 minutes.

Scenario: "Auderghem": Containers miscommunication

Level: Medium

Type: Fix

Access: Paid

Description: There is an nginx Docker container that listens on port 80, the purpose of which is to redirect the traffic to two other containers statichtml1 and statichtml2 but this redirection is not working.
Fix the problem.

IMPORTANT. You can restart all containers, but don't stop or remove them.

Test: The nginx container must redirect the traffic to the statichtml1 and statichtml2 containers:

curl http://localhost returns the Welcome to nginx default page
curl http://localhost/1 returns HelloWorld;1
curl http://localhost/2 returns HelloWorld;2

The "Check My Solution" button runs the script /home/admin/agent/check.sh, which you can see and execute.

Time to Solve: 15 minutes.