Load Balancers: Building Distributed Systems from Scratch Round robin, least connections, consistent hashing and others, you’ve read about these, maybe answered a system design question on them. But have you ever actually watched your load balancer route traffic to a dead backend because your health check interval was too long?

The gap between theory and reality shows up fast.

Practice Here: https://builddistributedsystem.com/tracks/loadbalancers…

Building Distributed Systems from Scratch

Source: https://builddistributedsystem.com/tracks/loadbalancers

Subtracks & Tasks

Layer 4 Load Balancing

Layer 7 Load Balancing

Advanced Balancing Algorithms

Interview Prep

Common interview questions forInfrastructure / Platform Engineerroles that map directly to what you build in this track. Click any question to reveal the model answer.

Questions are representative of real interview patterns. Model answers are starting points — adapt them with your own experience and the specific context of the interview.

Common Mistakes

The top5mistakes builders make in this track — and exactly how to fix them. Click any mistake to see the root cause and the correct approach.

Comparison Mode

Side-by-side comparisons of the approaches, algorithms, and trade-offs you encounter in this track. Expand any comparison to see a detailed breakdown.

Concepts Covered

round robinload balancingstatelessleast connectionsdynamic loadconnection trackinghealth checkfailoverlivenessLayer 7HTTP routingcontent-basedconsistent hashingkey affinitycache localitylayer 7 load balancingHTTP proxyrequest routingheader inspectionbackend selectionpath-based routingURL rewritingrouting tableswildcard matchingbackend poolssticky sessionssession affinitycookie-based routingsession persistencestateful servicescircuit breakerfailure thresholdhalf-open stateautomatic recoverycascade preventionrate limitingtoken bucketper-IP limitsper-API-key limitsDDoS protectionleast-connectionsactive connection trackingload-based routingatomic countersvariable request durationsweighted round-robincapacity-based routingbackend weightsheterogeneous clusterstraffic proportionalitypower-of-two-choicesrandomized load balancingleast-connections approximationconstant-time selectionscalabilitycache coherencyminimal disruptionbackend additions/removalsthundering herdcascading failuresexponential backoffgraceful degradationcircuit breaking

Prerequisites

It is recommended to complete the previous tracks before starting this one. Concepts build progressively throughout the curriculum.

For when you want to go deeper. Curated papers, posts, and talks beyond what this track covers.