Even after a lot of googling, I could not find a simple answer to this question. All I could find was it's layer 4 load balancer that can handle millions of requests per second, and support for static/elastic ip. Could someone please give me an example where network load balancers are used in real life? A simple use case. When to pick network load balancer over application load balancer?
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why the down vote? It's a noob question. – Shree Ranga Raju May 08 '20 at 01:40
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1Good question. I will upvote to balance the vote count ◡̈ – jellycsc May 08 '20 at 01:56
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2I didn't downvote, but FYI the definition of a down-vote is _"This question does not show any research effort; it is unclear or not useful"_. Also, some people just don't like non-programming questions appearing on StackOverflow. – John Rotenstein May 08 '20 at 06:53
2 Answers
When compared to an Application Load Balancer a simple explanation goes like this: Network Load Balancer is used anywhere where the application behind the balancer doesn't work over HTTP(S), but uses some other protocol. Including, but not limited to:
- Legacy applications that implement custom protocol.
- NTP servers.
- SMTP server.
- Database servers.
- MQTT brokers.
- High performance queue servers (ActiveMQ, RabbitMQ, ZeroMQ etc.).
- Message processing applications (think Kafka and Co.).

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I would like to complement @Sergey list with few more scenarios where NLB is useful:
NLB provides static IP address, ALB does not. So use it when you require a static IP for your LB. Similarly, it is the only balancer that can use Elastic IP addresses.
Use NLB when you require end-to-end SSL encryption. ALB will always terminate SSL connection, which may be not desired due to strict security requirements.
NLB is the only balancer type that can be used for API Gateway VpcLink or VPC PrivateLink technologies.
NLB does not have Security Groups.

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NLBs support security groups now. https://aws.amazon.com/about-aws/whats-new/2023/08/network-load-balancer-supports-security-groups/ – Aakash Aug 11 '23 at 01:47