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Layer 4 vs Layer 7

Connection-level versus request-level balancing, and what each unlocks.

4Questions
10Flashcards
3Terms
Drill this topic All of Networking
Questions

4 to work through

  1. beginner

    Six backends sit behind one load balancer: two in zone A and four in zone B. The zone A pair runs at 70% CPU while the zone B four sit at 25%. The load balancer's per-zone request counts are even and no target is unhealthy. What is happening?

    2 min answer
  2. intermediate

    A service has widely varying request costs — most complete in 10 ms, some take 5 s. Under round robin some instances are overwhelmed while others idle. What do you change?

    2 min answer
  3. advanced

    A chat platform's Layer 7 proxy tier holds millions of WebSocket connections. Every proxy deployment disconnects everyone. What would you change?

    2 min answer
  4. advanced

    One instance passes its health checks but serves requests ten times slower than its peers. Why is it still receiving traffic and what would you change?

    2 min answer
Terminology

3 terms in this topic

concept

Health Check Configuration

The interval, timeout, and healthy/unhealthy thresholds that together determine how quickly a failed backend leaves rotation.

 concept

Load Balancer Types

Layer 4 against layer 7, the algorithms that distribute requests, and why "least connections" is usually better than round robin.

 concept

Load Balancing Algorithm

The rule deciding which backend receives a request — round robin, least connections, least response time, or hash-based.
Networking

Neighbouring topics

Networking

General material on the network path underneath an architecture.

4 quiz 13 cards 14 terms

TCP/IP

Handshakes, congestion control, head-of-line blocking and connection reuse.

3 quiz 9 cards 2 terms

HTTP/1.1, HTTP/2 & HTTP/3

Multiplexing, prioritisation and the transport each is built on.

4 quiz 11 cards 5 terms

DNS

Resolution, TTL behaviour, traffic steering and failover latency.

5 quiz 7 cards 3 terms

TLS & Certificates

Encryption, integrity, authentication, termination points and expiry.

6 quiz 7 cards 5 terms

Reverse Proxies

One place for TLS, routing, caching, compression and rate limiting.

3 quiz 9 cards 5 terms

Content Delivery Networks

Edge caching, origin offload, spike absorption and dynamic content.

8 quiz 11 cards 6 terms

Firewalls & Security Groups

Default-deny, stateful rules, and restricting egress as well as ingress.

5 quiz 8 cards 3 terms

NAT & Egress

Outbound-only connectivity, its per-gigabyte cost and its zone binding.

4 quiz 11 cards 4 terms

VPC Design

Address planning, peering and the ranges you can never resize.

3 quiz 9 cards 3 terms

Subnetting

Tiering, zone binding, and sizing for an address-hungry platform.

3 quiz 9 cards 3 terms

Routing & BGP

How traffic finds you, anycast, and route withdrawal as a failure mode.

2 quiz 8 cards 5 terms

Service Mesh Networking

Sidecar proxies supplying mTLS, retries and traffic policy.

4 quiz 11 cards 3 terms

WebSockets & Realtime

Persistent bidirectional connections and the capacity model they impose.

6 quiz 13 cards 6 terms

gRPC Transport

HTTP/2 multiplexing, binary encoding and streaming semantics.

4 quiz 12 cards 3 terms

API Gateways

The single entry point, and the business logic that must stay out of it.

3 quiz 10 cards 4 terms

Network Performance

Latency floors, bandwidth-delay product, and what no code change fixes.

5 quiz 13 cards 5 terms

Private Connectivity

Private endpoints, peering and dedicated links to managed services.

4 quiz 7 cards 3 terms

Network Troubleshooting

Flow logs, packet paths, and localising a problem to a hop.

6 quiz 8 cards 3 terms