feat: 🎸 optional enable cross zone lb

[jaskaransarkaria]

Overview

This optimisation will only be disabled on the 'production-only' ingress

We can disable cross-zone load balancing because the nlb is created in each subnet, so traffic will still be able to reach each az. It is also worth mentioning that cross-zone load balancing for nlb is disabled by default.

When you enable an Availability Zone, you specify one subnet from that Availability Zone. Elastic Load Balancing creates a load balancer node in the Availability Zone and a network interface for the subnet (the description starts with "ELB net" and includes the name of the load balancer). Each load balancer node in the Availability Zone uses this network interface to get an IPv4 address
here

Diagram overview

disabled:

vs.

enabled:

Why

We want to be able to toggle cross-zone load balancing because it can introduce connection resets when a connection is mistakenly identified as originating from a duplicate source.

Disadvantages

The disadvantage of disabling cross-zone load balancing is if a client caches the DNS of the lb it could result in lbs receiving "disproportionally higher number of inbound requests"

Advantages

Benefits include fewer connection resets, marginally reduced latency (not crossing AZs) and reduced regional data transfer charges

$0.010 per GB - regional data transfer - in/out/between EC2 AZs or using elastic IPs or ELB # https://cloudiamo.com/2019/01/24/cross-zone-load-balancing-always-on-right/

Dig

You can see the nlb in each subnet az with dig below:

; <<>> DiG 9.10.6 <<>> a9a1fce6427fd49058c4c68e57fd8e75-e2e37f01a215aa62.elb.eu-west-2.amazonaws.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36420
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;a9a1fce6427fd49058c4c68e57fd8e75-e2e37f01a215aa62.elb.eu-west-2.amazonaws.com. IN A

;; ANSWER SECTION:
a9a1fce6427fd49058c4c68e57fd8e75-e2e37f01a215aa62.elb.eu-west-2.amazonaws.com. 60 IN A 13.42.229.97
a9a1fce6427fd49058c4c68e57fd8e75-e2e37f01a215aa62.elb.eu-west-2.amazonaws.com. 60 IN A 3.10.250.16
a9a1fce6427fd49058c4c68e57fd8e75-e2e37f01a215aa62.elb.eu-west-2.amazonaws.com. 60 IN A 18.135.147.246

;; Query time: 34 msec
;; SERVER: 100.64.9.0#53(100.64.9.0)
;; WHEN: Tue Mar 26 09:40:21 GMT 2024
;; MSG SIZE  rcvd: 154