Optional Extension: Enable Caching in Nginx (Reverse Proxy Lab)

1. Goal

In this extension you will:

Configure Nginx to cache responses from the backend pool
Verify that repeated requests are served from cache
Observe cache behavior when you change backend responses

You should add this on top of your existing loadbalance.local setup.

2. Step 1 – Define a Cache Path

Edit the main Nginx config file:

sudo nano /etc/nginx/nginx.conf

Inside the http { ... } block, add:

proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=mycache:10m
                 max_size=100m inactive=60m use_temp_path=off;

Explanation:

mycache:10m – name of cache zone + metadata size
max_size=100m – limit cache size
inactive=60m – cached items not accessed for 60 minutes are removed

Save and exit.

3. Step 2 – Enable Cache in Your Server Block

Edit your site config:

sudo nano /etc/nginx/sites-available/loadbalance.local

Inside the server { ... } block, modify your location /:

location / {
    proxy_cache mycache;
    proxy_cache_valid 200 1m;
    add_header X-Proxy-Cache $upstream_cache_status;
 
    proxy_pass http://backend_pool;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
}

Explanation:

proxy_cache mycache; – use the cache zone configured earlier
proxy_cache_valid 200 1m; – cache HTTP 200 OK responses for 1 minute
X-Proxy-Cache – custom header with cache status (MISS, HIT, BYPASS, …)

Test and reload:

sudo nginx -t
sudo systemctl reload nginx

4. Step 3 – Test the Cache

4.1 Initial Request

Run:

curl -I http://loadbalance.local/

Look for the header:

X-Proxy-Cache: MISS

The first request typically results in MISS (nothing cached yet).

4.2 Subsequent Requests

Run:

for i in {1..5}; do curl -I http://loadbalance.local/; done

You should now see:

X-Proxy-Cache: HIT

This indicates the response is being served from cache.

5. Step 4 – Verify Cache Duration

Wait at least 1 minute (based on proxy_cache_valid 200 1m).
Call again:
```
curl -I http://loadbalance.local/
```

You should see the status go back to MISS, then HIT again on later requests.

6. Step 5 – Observe Caching Effects

Try changing one backend to respond differently (e.g. backend 1 returns {"backend":"1-changed"}) while the cache is active.

You may still see the old data until cache expires.
This shows that clients are no longer hitting backends directly for each request.

Describe your observations in your protocol:

How did the X-Proxy-Cache header change?
When did you see updated backend responses?

Deep Thought

Explorer

Linux Exercise 11a - optional - Caching