When you go to production with gRPC, make sure you’ve solved load distribution first.
I was recently talking with another engineer who is rolling out gRPC into production. He asked what the biggest gotchas were.
My first answer: Load Distribution.
🚦 HTTP/1 vs. HTTP/2
Most teams first implement services using REST over HTTP/1 and then migrate to gRPC as they seek its performance benefits.
That shift introduces a subtle but important change in how traffic gets distributed across instances.
With HTTP/1, requests are generally tied closely to connections. A client opens a connection, sends a request, waits for the response, and then sends another (if connection re-use is enabled).
HTTP/2 (which underpins gRPC) works differently.
HTTP/2 multiplexes requests over persistent connections. A client can send many requests over the same connection without waiting for responses.
This is one of the reasons gRPC provides a performance boost, but it can create unexpected load distribution issues.
If your infrastructure isn’t built for an HTTP/2 world, you’ll quickly find traffic becoming unevenly distributed.
🏗️ Infrastructure Support
In an HTTP/1 world, load balancing at the connection (Layer 4) level often works well enough. But with HTTP/2, connections live much longer and carry far more concurrent traffic.
If your load balancer distributes traffic based only on connections, a busy client may hammer a single instance while others sit idle.
Unfortunately, much of the infrastructure still doesn’t fully support HTTP/2-aware load balancing.
Depending on your environment, your load balancers or ingress controllers may operate primarily at Layer 4. That works fine for HTTP/1, but once you introduce HTTP/2 via gRPC, the effectiveness changes significantly.
⚙️ Supporting gRPC
To get the most out of gRPC, the best approach is to use infrastructure that understands HTTP/2 and load-balances requests rather than just connections.
If that’s not possible, another option is client-side load balancing.
Many gRPC clients support opening a pool of connections and distributing requests across them. You still benefit from HTTP/2’s persistent connections, but you avoid concentrating all traffic on a single backend instance.
🧠 Final Thoughts
gRPC offers many advantages, including performance, strongly typed contracts, and efficient communication. But it also introduces different networking behavior.
If you’re rolling out gRPC into production, make sure your load balancing infrastructure is ready for an HTTP/2 world.