Tech World Software SchoolTWSS
0x50Lesson 6 of 6

Operate load balancers reliably

Plan TLS termination, zonal resilience, capacity, and useful traffic signals.

12 min 5-question quiz
By the end of this lesson you can
  • Identify key load-balancer failure modes and interpret request-level metrics.

At TLS termination, a balancer handles certificates and decrypts traffic before forwarding it; re-encryption can protect the backend hop too. Deploy balancers and backends across failure zones, avoid a single overloaded entry point, and test failover. Monitor request rate, error rate, latency percentiles, active connections, rejected connections, backend health, and per-backend imbalance. A balancer can shed load or return a controlled error instead of letting queues grow without bound.

Metrics should be split by backend pool, zone, and response class where useful. Watch both aggregate results and skew: a healthy average can hide one failing backend or one saturated zone.

Practice: follow TLS through the balancer

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Up to 15 XP

Where is the traffic encrypted?

Step through a request that’s re-encrypted for the backend hop.

Message 1 of 5Predicted 0/0
Client
Load balancer
Backend

Practice: read traffic metrics

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Up to 15 XP

Why percentiles matter

These are request latencies in milliseconds. Click near 900 on the chart a few times to add slow requests. How far does the median move, compared with the slowest requests? An average can look fine while real customers wait.

mean0250500750100042 ms - click to remove48 ms - click to remove51 ms - click to remove55 ms - click to remove58 ms - click to remove60 ms - click to remove64 ms - click to remove70 ms - click to remove75 ms - click to remove82 ms - click to remove

Click the line to add a value; click a dot to remove it. Red dots are outliers by Tukey’s rule (more than 1.5 × IQR beyond the box).

Mean

60.5 ms

Median

59.0 ms

Std. deviation

12.5 ms

IQR (Q3 − Q1)

21.0 ms

n = 10

Try it

Up to 15 XP

Find the problem hiding in the average

The pool’s dashboard is green. Click the line that explains what customers are complaining about.

Round 1 of 2: One bad backendScore 0/0

Which line shows where the failures are coming from?

Pool checkout: last 5 minutes

Key takeaways

  • Plan TLS behavior and backend-hop protection explicitly.

  • Use multiple failure zones and test failover.

  • Monitor percentiles, errors, connections, and imbalance at both pool and backend level.

Lesson quiz

5 questions · pass with 4 correct · up to 50 XP

Passing this quiz completes the lesson and keeps your streak going. Questions you miss come back in review sessions later.

Questions about this lesson

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