Imagine your website has servers in Mumbai and Frankfurt. A visitor in India probably shouldn’t cross half the planet just to reach Frankfurt. That’s where global server load balancing, or GSLB, starts to matter.
Where GSLB Fits With a Reverse Proxy
A reverse proxy already hides your backend servers from users. It can receive a request and pass it to an application server without exposing that server directly. Add GSLB above that setup and the decision becomes broader.
Instead of asking only, “Which backend server is free?” the system can ask, “Which location should handle this request?” Geography matters. So does server health. Network conditions matter too.
The Basic Flow
A visitor enters your domain. The GSLB layer looks at the request and chooses an appropriate site or proxy endpoint. That reverse proxy then handles the request and sends it toward the right backend.
• Geography plays a part, though it isn’t the whole decision.
• A healthy server in Singapore is more useful than a dead one in Mumbai, even if the visitor is sitting in Mumbai.
• DNS is often involved, and this is where things get interesting because DNS-based GSLB has its own limits.
Why Put GSLB in Front of Reverse Proxies?
The main reason is distance. If your users are spread across regions, sending everyone to one data center creates unnecessary delay. A nearby reverse proxy generally feels quicker because the request has less network distance to cover.
But performance isn’t the only reason. GSLB also gives you a way to shift traffic when one location has trouble. If the Frankfurt site goes down, traffic can be directed elsewhere, assuming the other location has enough capacity.
That’s a big deal for global services. You don’t want a single regional failure turning into a worldwide outage.
Health Checks Change the Game
GSLB needs some idea of what is actually working. Health checks provide that signal. The system can test a service or endpoint and stop directing new traffic toward a location that has failed its checks.
This sounds obvious. It isn’t always simple.
A server might respond successfully while the application behind it is broken. Good GSLB setups therefore check something meaningful, not merely whether a machine answers a basic network request.
The Part People Often Miss
GSLB isn’t magic traffic teleportation. DNS caching can affect how quickly routing changes reach users. A browser or resolver may keep an old answer longer than you’d like.
And that’s why I prefer thinking of GSLB as a traffic decision layer rather than simply a “fastest server” feature. It gives the system context before the reverse proxy does its normal work.