WebSocket proxying in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

WebSocket connection upgrade headers

You have an Nginx configuration proxying WebSocket traffic. What is the output of the following curl command headers when connecting to the WebSocket endpoint?

curl -i -N -H "Connection: Upgrade" -H "Upgrade: websocket" http://localhost/ws

A HTTP/1.1 200 OK\nContent-Type: text/html

B HTTP/1.1 400 Bad Request\nContent-Type: text/plain

C HTTP/1.1 101 Switching Protocols\nUpgrade: websocket\nConnection: Upgrade

D HTTP/1.1 404 Not Found\nContent-Type: text/html

💡 Hint

WebSocket connections require HTTP 101 status with upgrade headers.

When Nginx proxies WebSocket correctly, it responds with HTTP 101 Switching Protocols and includes Upgrade and Connection headers to establish the WebSocket connection.

❓ Configuration

intermediate

Correct Nginx config for WebSocket proxy

Which Nginx configuration snippet correctly enables WebSocket proxying to backend at ws://backend:8080/ws?

A proxy_set_header Upgrade $http_upgrade;\nproxy_set_header Connection "upgrade";\nproxy_pass http://backend:8080/ws;

B proxy_set_header Upgrade websocket;\nproxy_set_header Connection keep-alive;\nproxy_pass http://backend:8080/ws;

C proxy_set_header Upgrade $http_upgrade;\nproxy_set_header Connection "close";\nproxy_pass http://backend:8080/ws;

D proxy_set_header Upgrade $connection_upgrade;\nproxy_set_header Connection "close";\nproxy_pass http://backend:8080/ws;

💡 Hint

The Upgrade header must use the client header variable, and Connection must be 'upgrade'.

To proxy WebSocket, Nginx must forward the client's Upgrade header using $http_upgrade and set Connection to 'upgrade'. Other values break the WebSocket handshake.

❓ Troubleshoot

advanced

WebSocket connection fails with 400 Bad Request

You configured Nginx to proxy WebSocket but clients get HTTP 400 Bad Request errors. Which is the most likely cause?

A Client is using HTTP/2 instead of HTTP/1.1

B Backend server is down and not responding

C Nginx is missing SSL certificate configuration

D Missing or incorrect Upgrade and Connection headers in proxy_set_header directives

💡 Hint

WebSocket handshake requires specific headers to upgrade the connection.

If Nginx does not forward the Upgrade and Connection headers correctly, the backend rejects the handshake causing 400 errors.

🔀 Workflow

advanced

Steps to enable WebSocket proxying in Nginx

What is the correct order of steps to enable WebSocket proxying in Nginx?

A 2,3,1,4

B 1,3,2,4

C 2,1,3,4

D 1,2,3,4

💡 Hint

Headers must be set before proxy_pass, then reload Nginx.

First set the headers to handle WebSocket upgrade, then proxy_pass to backend, finally reload Nginx to apply changes.

✅ Best Practice

expert

Best practice for WebSocket timeout settings in Nginx

Which Nginx configuration snippet follows best practices to avoid WebSocket connection drops due to timeouts?

A proxy_read_timeout 30s;\nproxy_send_timeout 30s;

B proxy_read_timeout 3600s;\nproxy_send_timeout 3600s;

C proxy_connect_timeout 5s;\nproxy_send_timeout 10s;

D proxy_connect_timeout 60s;\nproxy_read_timeout 10s;

💡 Hint

WebSocket connections are long-lived and need longer timeouts.

Setting long proxy_read_timeout and proxy_send_timeout prevents Nginx from closing idle WebSocket connections prematurely.