★ FEATURED ARTICLE 中文版 GitHub: https://github.com/geekchow/aws-lambda-guideWhere you are:Stage 4 of 6 (Running example).After this file you will know:the one scenario every later file refers back to, and which component is on stage at each step — still without internals.The scenario in three sentencesOnThursday 2026-11-26, ShopFast’s team ships coupon support asversion 8of thecheckoutfunction, shifting theprodaliasfrom v7 to v8 by canary (10% for 10 minutes, then 100%).Before the sale opens onFriday 09:00, they raiseprovisioned concurrencyonprodfrom 50 to 400 so the first wave of shoppers never sees a cold start.At 09:05 a viral post pushes traffic beyond the warm pool: extra requestsspill overto cold on-demand environments, and at the very top a few arethrottledby the function’s reserved concurrency cap.The cast (fixed facts used everywhere)ItemValueAccount / Region111122223333/us-east-1Functioncheckout, Node.js 22 runtime, 1,024 MB memory, 10 s timeoutCallerAPI (Application Programming Interface) Gateway REST API, integration ARN (Amazon Resource Name)arn:aws:lambda:us-east-1:111122223333:function:checkout:prodVersionsv7 (current), v8 (new, coupons)Aliasprod→ v7, PC (Provisioned Concurrency) 50Reserved concurrency800 (socheckoutcan never starve other functions, nor be starved)Average duration150 ms warm; cold Init ≈ 600 msAccount concurrency quota3,000Three named requests we follow:RequestWhenFateAlice’s checkoutThu 14:05, during the canaryLands on v8 (the 10%), served by a warm PC environmentBob’s checkoutFri 09:05, the viral spikePC pool full → spillover → cold start on a new v8 environmentCarol’s checkoutFri 09:06, the very peakReserved concurrency of 800 reached →429throttle; API Gateway returns an error, the client retriesThe scenario traced shallowlyQuestion it answers: in what order do the players appear across the week?Friday: the sale08:30 Auto Scaling setsPC to 400Placement boots 400v8 envs, Init runs09:00 2,000 RPS,300 concurrent: all warm09:05 Bob: PC full,spillover cold start09:06 Carol: 800 cap hit,429 throttleThursday: deployCI updates code of$LATESTVersion store publishesv8Alias prod becomesv7 90 / v8 10PC manager splits warmpool across v7 and v8Alice request routedto v8, warm envAlarms quiet:prod v8 100Caption: the week in ten steps — the spine every depth dive anchors to.Thursday — deploying v8(T1–T2)The CI/CD (Continuous Integration / Continuous Delivery) pipeline uploads the new zip to thefunction’s$LATEST, then callsPublishVersion. TheVersion storefreezes code config asversion 8.(T3)CodeDeploy updates thealiasprod: primary v7, additional version v8 with weight 0.10. API Gateway’s integration still sayscheckout:prod— nothing on the caller side changes.(T4)Becauseprovisioned concurrencyis configured onprod, thePC managernow keeps warm environments forbothversions, roughly in proportion to the weights.(T5)Aliceclicks “Pay”. API Gateway invokescheckout:prod. TheInvoke Frontendauthenticates the call, thealias routerrolls the weighted dice → v8. TheCounting serviceconfirmscheckoutis under its limits. TheAssignment servicefinds an idle, pre-initialized v8execution environmentand the handler runs in ~150 ms. No cold start.(T6)Ten quiet minutes later CodeDeploy setsprod→ v8 at 100%. (Had errors spiked, it would have set the weight back to 0 — a rollback in seconds.)Friday — the sale(F1–F2)At 08:30 a scheduled action inApplication Auto Scalingraises PC onprodto 400. ThePC managerasksPlacementfor 400 v8 environments; each runs itsInitphase now, not during a request.(F3)At 09:00, 2,000 RPS (Requests Per Second) × 0.15 s ≈300 concurrentinvocations. Every one lands on a warm PC environment.(F4)At 09:05 traffic jumps to ~4,500 RPS → ~675 needed. The 400 PC environments are busy;Bob’s request is admitted by Counting (675 800) but the Assignment service has no idle environment, soPlacementcreates a new on-demand v8 environment. Bob waits ~600 ms extra: acold start(aspilloverinvocation).(F5)At 09:06 demand briefly needs ~850.Carol’s request is the 801st concurrent one; theCounting servicerejects it with429.What each step touchesConcept / playerStepsFunction /$LATEST1Version (Version store)1, and every later step runs “v8”Alias (alias router)2, 4, 5Provisioned concurrency (PC manager Auto Scaling)3, 6, 7, 8Invocation concurrency (Frontend Counting)4, 7, 8, 9Assignment Placement4, 6, 8Execution environment4, 6, 7, 8Test yourself:without scrolling up, who rejects Carol, and why isn’t that the PC manager’s job? (Answer: the Counting service, because PC never caps traffic — it only pre-warms.)Next →05.1 Versions ·Back to03 Concept map Back to series index
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