This is good advice. Ideally, never blend your AZs, each should be an independent stack. Use 3+ not 2, keeps you honest about an availability strategy instead of a standby failover strategy. In front of them, use DNS geo IP or even basic round robin (with service availability check) to get to the NLB. Behind the NLB, stay in that AZ!
If you need to call out of the the AZ for other data or API sources, either figure out which AZs that service is using and configure to stay in them, or, make sure to go all the way back out to a well-balanced (for resilience) endpoint.
If you need to call out of the the AZ for other data or API sources, either figure out which AZs that service is using and configure to stay in them, or, make sure to go all the way back out to a well-balanced (for resilience) endpoint.