Explain like I'm five · SRE

What is Capacity Planning?

Capacity planning, told as a story about looking at last year's numbers and this year's events to add rides and staff ahead of time.

FULLthe line never gets shortereveryone came for vacation... and they're all leavingpeak summer — not enough rides, not enough booths

At peak season, not enough rides or booths for the crowd.More guests came for vacation, and most of them just leave.

USUAL DAYline of 43 rides is enoughholidays bring 3xit's always been about this much...planning for a usual day can't survive a holiday or event day

Planning for a usual day can't survive a special one.A holiday or an event day can bring several times the usual crowd.

LAST YEARJuly avg. 400holiday wknd 1200-> likely more this yearlook at last year and this year's events, then add rides and staff in advancenot scrambling last-minute — counted and added ahead of time

Look at last year and this year's events, then add in advance.Not scrambling last-minute — counted and prepared ahead of time.

Check last year's numbershow many came back then
Check special daysevents and sale days
Leave some bufferexact numbers are risky
Test it beforehandto see if it really holds
THIS YEAR'S PLANlast July: 400 gueststhis July (est.): 550rides 3 -> 4staff 6 -> 9a bit of buffer toolast year's numbers + this year's events = how much more you need

Last year's numbers plus this year's events tell you how much more you need.Add that many more rides and staff, with a little extra buffer on top.

more always show up than plannedSO WE PAIR IT UPplan ahead+ auto-call more staffboth together, and it's safeeven careful counting can fall short — pair it with calling in more automatically when lines grow

More always show up than planned — so it's paired with automatic response.Planning alone can fall short. You need it paired with automatically calling in more to feel safe.

In one breath

Capacity planning = looking at last year's numbers and this year's events to calculate in advance how much more you'll need, and adding rides and staff before the rush.

The practice of forecasting future traffic from historical usage trends and planned events (sales, holidays, marketing campaigns) to prepare infrastructure ahead of time. Demand forecasting estimates how much you'll need, a buffer adds a safety margin, and load testing confirms it actually holds up.

When grown-ups say it

Capacity planning
Counting in advance how much you'll need. Applies to rides, staff, and servers alike.
Demand forecasting
Guessing how many more will come. Looking at last year's numbers together with this year's events.
Load testing
Testing beforehand whether it really holds that much. Prepare without testing, and you hit peak season not knowing for sure.
Peak traffic
The moment the most guests arrive. Holidays, sales, and events can bring several times the usual load.
Buffer (headroom)
The extra left over instead of cutting it exactly even. The cushion that lets you survive a wrong guess.
Relation to automatic scaling
Even careful planning is paired with automatically calling in more. Planning ahead and automatic response together — that's what makes it safe.
Relation to SRE
One piece of the whole job of keeping the park running. Used together with gauges, automation, and paging. → the people who keep an amusement park open
Cost of over-provisioning
Add too much, and money goes out for rides that never fill. Too little loses guests; too much wastes money — balance is the point.
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