Linux Exercise 11c - optional - Weighted-Load-Balancing

Optional Extension: Weighted Load Balancing with Nginx

1. Goal

In this extension you will:

• Configure weighted load balancing for your backend pool
• Make one backend receive more traffic than the other
• Verify the distribution using curl

Weights are useful when:

• One backend server has more CPU/RAM
• You want to gradually shift traffic to a new version (canary style)

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2. Step 1 – Configure Weighted Upstream

Edit:

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

Find your upstream block and adjust it as follows (ensure ip_hash is NOT used here):

upstream backend_pool {
    server 127.0.0.1:8001 weight=3;
    server 127.0.0.1:8002 weight=1;
}

Explanation:

• Backend 1 has weight 3
• Backend 2 has weight 1
• Ratio of requests: ~3:1 (about 75% vs 25%)

Save, test, and reload:

sudo nginx -t
sudo systemctl reload nginx

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3. Step 2 – Test the Distribution

Run multiple requests:

for i in {1..20}; do curl http://loadbalance.local/; echo; done

Count how many times you see each backend:

• {"backend":"1"}
• {"backend":"2"}

You should see backend 1 significantly more often than backend 2.

For a more precise count, you can use:

for i in {1..50}; do curl -s http://loadbalance.local/; echo; done | sort | uniq -c

This will group and count occurrences.

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4. Step 3 – Try Different Ratios

Experiment by changing the weights:

upstream backend_pool {
    server 127.0.0.1:8001 weight=5;
    server 127.0.0.1:8002 weight=1;
}

Or:

upstream backend_pool {
    server 127.0.0.1:8001 weight=1;
    server 127.0.0.1:8002 weight=3;
}

Each time:

1. Save the file
2. Run sudo nginx -t
3. Run sudo systemctl reload nginx
4. Perform the test loop again

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5. Step 4 – Document Your Observations

In your protocol, describe:

• The weight values you tried
• The approximate ratio of responses you observed
• How weights could be used in real deployments, e.g.:
  • Slowly shifting traffic to a new version
  • Sending most traffic to a more powerful server
  • “Canary testing” a new backend for a small percentage of users