1 Introduction
2 Scalability Spectrum
2.1 Basic Model
2.2 Asymptotic Scaling Regimes
2.3 Basic Load Balancing Algorithms
2.4 Performance Comparison
3 Preliminaries, JSQ Policy, and Power-of d Algorithms
3.1 Definitions, Limit Sequences, and Convergence Issues
3.2 Fluid Limit for JSQ(d) Policies
3.3 Fluid Limit for JSQ Policy
3.4 Diffusion Limit for JSQ Policy
3.5 JSQ(d) Policies in Heavy-Traffic Regime
4 Universality of JSQ(d) Policies
4.1 High-Level Outline of Proof Approach
4.2 Extension to Batch Arrivals
5 Blocking and Infinite-Server Dynamics
5.1 Fluid Limit for JSQ Policy
5.2 Diffusion Limit for JSQ Policy
5.3 Universality of JSQ(d) Policies in Infinite-Server Dynamics
6 Load Balancing in Graph Topologies
6.1 Asymptotic Optimality Criteria for Deterministic Graph Sequences
6.2 Asymptotic Optimality of Random Graph Sequences
7 Token-Based Load Balancing
7.1 Fluid-Level Optimality of JIQ Scheme
7.2 Diffusion-Level Optimality of JIQ Scheme
7.3 Multiple Dispatchers
7.4 Joint Load Balancing and Auto-Scaling
8 Redundancy Policies and Alternative Scaling
8.1 Redundancy d Policies
8.2 Conventional Heavy Traffic
8.3 Non-Degenerate Slowdown
8.4 Sparse-Feedback Regime
8.5 Scaling of Maximum Queue Length