What Happens When Code Runs Inside the Kernel?

Hey there,

What if you could extend your operating system’s capabilities without touching its source code, rebooting the kernel, or risking a crash?

For a long time, developers who needed custom kernel functionality had two choices: write risky kernel modules that could destabilize the entire system, or accept the limitations of the kernel's out-of-the-box functionality.

eBPF changed that equation.

In today’s issue, we look at eBPF’s role in the Linux kernel and how Cilium leverages it for faster, safer cloud-native systems.

Let’s dive in

eBPF (Extended Berkeley Packet Filter) lets you run lightweight programs directly inside the Linux kernel in response to system events. Whether a packet hits the network, a process writes to disk, or an application makes a system call, eBPF can react instantly and handle data at the source in real time.

Your operating system has three layers: hardware at the base, the kernel in the middle managing resources, and user applications at the top. Developers can write eBPF programs in high-level languages like C, compile them into bytecode, and use system calls to load them into the kernel. Once inside, they attach to specific event hooks.

When an application makes a system call, it triggers an event. The eBPF program responds instantly, processing data without switching between user space and kernel space. This design keeps performance high and latency low.

Unlike traditional kernel modules that required deep integration and came with crash risks, eBPF programs avoid these issues entirely by running in isolation from the core kernel. This approach lets developers:

• Add or remove functionality without risking kernel crashes

• Deploy updates without restarting the kernel

• Make real-time changes while keeping systems running smoothly

• Execute programs exactly where they’re needed for better performance

Cilium is a platform purpose-built for Kubernetes environments that uses eBPF to manage networking and security. Instead of routing data through legacy tools like iptables, it processes traffic within the kernel itself, speeding up connections and improving visibility.

With eBPF, Cilium can:

• Deliver faster network connections with minimal delay

• Enforce security policies that adapt as networks evolve

• Monitor traffic in real time for deeper insights

• Optimize resource use by handling data where it originates

In distributed systems, that’s a huge difference. Traditional user-space tools shuffle data back and forth, creating overhead. Cilium, powered by eBPF, acts right where the data lives, ensuring better performance and a more accurate view of your infrastructure.

eBPF is quietly reshaping how developers build, secure, and monitor cloud systems. It’s the foundation behind tools like Cilium that bring kernel-level observability and performance into cloud-native systems.

Check out the blog post here to see how eBPF works and why it matters.

And it’s a wrap!

See you Friday for the week’s news, upcoming events, and opportunities.

If you found this helpful, share this link with a colleague or fellow DevOps engineer.

Divine Odazie
Founder of EverythingDevOps