SRE Capacity Planning & Scaling 3

Question 1

Which scaling pattern is most appropriate when a system's bottleneck is stateful session data?

Accepted Answer

Horizontal scaling with sticky sessions or a shared session store

Answer

Stateful sessions require either sticky sessions to route users to the same instance or a shared session store (like Redis) to allow any instance to serve any user.

Question 2

What is the 'utilization law' in the context of queuing theory for SRE capacity planning?

Accepted Answer

As utilization approaches 100%, queue length and wait time grow toward infinity

Answer

Queuing theory shows that as server utilization approaches 100%, queue lengths grow unboundedly, which is why SREs target utilization well below 100%.

Question 3

An e-commerce platform expects 10× normal traffic on Black Friday. Which capacity strategy best balances cost and reliability?

Accepted Answer

Pre-warm to 10× days before, then scale down gradually after

Answer

Pre-warming days before the event ensures capacity is ready and proven stable, while gradual scale-down avoids sudden drops in available capacity during lingering traffic.

Question 4

What does 'N+1 redundancy' mean in the context of capacity planning?

Accepted Answer

Having one extra unit of capacity beyond what is minimally required to handle load

Answer

N+1 redundancy means provisioning one additional unit above what is needed, so the system can absorb the loss of any single unit without degrading capacity.

Question 5

A microservice shows memory usage growing 5% per week. Which action should the SRE prioritize?

Accepted Answer

Investigate for a memory leak while monitoring the growth trend

Answer

Steady growth suggests a memory leak; the correct response is to investigate the root cause while tracking the trend to determine urgency.

(SRE) Site Reliability Engineering Foundation Certification Practice Test

(SRE) Site Reliability Engineering Foundation Certification Practice Test

SRE Capacity Planning & Scaling 3