Google's Global Load Balancer vs. DNS Load Balancing

DNS Load Balancing is tricky. For an app hosted in multiple regions, each region essentially gets an IP address that is unique - though mapped to the same domain name. For 3 regions, there are 3 IP addresses that are maintained by the DNS system.

What GCP does is provide you with a SINGLE VIP. This IP address is configured only ONCE in your Cloud DNS.

Once configured, this is the same IP that is presented to client machines in ALL regions. Behind the scenes, each region is routed to the nearest backend cluster.

GCP Network Load Balancer

This is purely layer 3 - so no SSL termination etc. is supported. All higher layer traffic just flows right through.  The advantage though is that client IPs are visible to the Load Balancer - and to the Backend instances. This allows one to whitelist / blacklist IP ranges using regular firewall rules. These are REGIONAL only (not global) in nature.

What if you needed both - Layer 3 Load Balancing and a Single IP Exposed (no DNS load balancing)?

Well - there's a load balancer for that as well. It's called TCP Proxy - and it exposes a single IP, while acting as a proxy. From Google's documentation

TCP Proxy Load Balancing lets you use a single IP address for all users worldwide. The TCP proxy load balancer automatically routes traffic to the backends that are closest to the user.

With Premium Tier, TCP Proxy Load Balancing can be configured as a global load balancing service. With Standard Tier, the TCP proxy load balancer handles load balancing regionally.

What if you need all of the above ALONG with SSL offloading?

Layer 3 load balancing, global in nature AND ssl offloading - calls for the SSL Proxy. This is the same as TCP Proxy, except for the SSL offloading option.

Summary

Load Balancers can be divided based on EXTERNAL / INTERNAL.  Or based on REGIONAL (Network) vs. Global (Https or Cloud Load Balancer). Or they can also be divided in terms of SSL Termination (any layer 7 Load balancer and also TCP Proxy) / No SSL Termination.

Google's Global Load Balancers are game changers because of the simplicity of configuring and maintaining them. These happen to be used internally by Google themselves (for gmail and other services).