Deep Dive into Tetragon

Introduction

In the evolving landscape of cloud-native security, traditional security tools often struggle to provide deep visibility without introducing significant performance overhead. Enter Tetragon, a CNCF project and sub-project of Cilium that leverages eBPF (extended Berkeley Packet Filter) to deliver powerful security observability and runtime enforcement capabilities directly in the Linux kernel.

Tetragon represents a fundamental shift in how we approach runtime security by applying policy and filtering at the kernel level, enabling security teams to detect and respond to threats with minimal latency and overhead.

What is Tetragon?

Tetragon is a flexible, Kubernetes-aware security observability and runtime enforcement tool that uses eBPF to monitor system-level events and enforce security policies. Unlike traditional security tools that operate in user space, Tetragon operates in the kernel, allowing it to:

Track any process with complete lifecycle visibility
Apply filtering and policy enforcement directly in eBPF
Generate enriched events with Linux and Kubernetes metadata
React to security-significant events in real-time
Minimize observation overhead through kernel-level processing

Core Architecture and Concepts

eBPF: The Foundation

eBPF allows Tetragon to safely run sandboxed programs in the Linux kernel without changing kernel source code or loading kernel modules. This provides several advantages:

Low overhead: Direct kernel-level processing eliminates the need for expensive context switches to user space
Real-time enforcement: Security policies can be enforced immediately at the point of execution
Deep visibility: Access to kernel-level events that would be difficult or impossible to observe from user space
Safety: eBPF programs are verified before execution to ensure they don’t crash the kernel

Sensors and Event Generation

Tetragon observes critical kernel hooks through its sensors, generating various types of events:

Process Lifecycle Events: By default, Tetragon generates process_exec and process_exit events, providing complete process lifecycle observability
Generic Tracing Events: Including process_kprobe, process_tracepoint, and process_uprobe for advanced custom use cases
Network Events: Monitoring network connections, socket operations, and traffic patterns
File System Events: Tracking file access, modifications, and permission changes

TracingPolicy: The Heart of Tetragon

TracingPolicy is Tetragon’s custom resource that defines what to observe and how to respond. A TracingPolicy consists of several key components:

Hooks: Define which kernel functions or system calls to monitor (e.g., kprobes, tracepoints)

Arguments: Specify the types and details of function arguments to capture

Selectors: Act as filters to narrow down which events trigger the policy (e.g., specific file paths, process names, or argument values)

Actions: Define responses to matched events, including logging, alerting, or enforcement actions like terminating processes

Kubernetes Integration

One of Tetragon’s standout features is its native Kubernetes awareness. It understands Kubernetes identities such as namespaces, pods, and containers, allowing security policies to be configured at the workload level. This means you can:

Apply different policies to different namespaces or pods
Correlate security events with specific Kubernetes resources
Enrich events with Kubernetes metadata automatically
Implement pod-specific security controls

Real-World Use Cases

1. Sensitive File Monitoring

Monitor access to critical system files like /etc/passwd, /etc/shadow, or application configuration files. Here’s a conceptual example:

apiVersion: cilium.io/v1alpha1
kind: TracingPolicy
metadata:
  name: monitor-sensitive-files
spec:
  kprobes:
  - call: "security_file_open"
    syscall: false
    args:
    - index: 0
      type: "file"
    selectors:
    - matchArgs:
      - index: 0
        operator: "Prefix"
        values:
        - "/etc/passwd"
        - "/etc/shadow"
      matchActions:
      - action: Post

2. Network Egress Control

Detect and optionally block unauthorized network connections, particularly useful for preventing data exfiltration:

apiVersion: cilium.io/v1alpha1
kind: TracingPolicy
metadata:
  name: monitor-external-connections
spec:
  kprobes:
  - call: "tcp_connect"
    syscall: false
    args:
    - index: 0
      type: "sock"
    selectors:
    - matchArgs:
      - index: 0
        operator: "NotDAddr"
        values:
        - "10.0.0.0/8"
        - "172.16.0.0/12"
        - "192.168.0.0/16"
      matchActions:
      - action: Post

3. Privilege Escalation Detection

Monitor system calls that could indicate privilege escalation attempts:

apiVersion: cilium.io/v1alpha1
kind: TracingPolicy
metadata:
  name: detect-privilege-escalation
spec:
  kprobes:
  - call: "sys_setuid"
    syscall: true
    args:
    - index: 0
      type: "int"
    selectors:
    - matchArgs:
      - index: 0
        operator: "Equal"
        values:
        - "0"
      matchActions:
      - action: Post

4. Runtime Enforcement

Beyond observation, Tetragon can enforce policies by taking action when violations are detected:

SIGKILL: Terminate processes that violate policies
Override: Use kernel error injection to make system calls fail (requires CONFIG_BPF_KPROBE_OVERRIDE)
Return value modification: Alter the return values of functions to prevent malicious behavior

Example enforcement policy:

apiVersion: cilium.io/v1alpha1
kind: TracingPolicy
metadata:
  name: prevent-etc-passwd-modification
spec:
  kprobes:
  - call: "sys_symlinkat"
    syscall: true
    args:
    - index: 0
      type: "string"
    - index: 1
      type: "int"
    - index: 2
      type: "string"
    selectors:
    - matchArgs:
      - index: 0
        operator: "Equal"
        values:
        - "/etc/passwd"
      matchActions:
      - action: Override
        argError: -1

Getting Started with Tetragon

Installation

Tetragon can be installed in several ways:

As a standalone binary:

curl -L https://github.com/cilium/tetragon/releases/latest/download/tetragon-linux-amd64.tar.gz | tar -xz
./tetragon

In Kubernetes using Helm:

helm repo add cilium https://helm.cilium.io
helm install tetragon cilium/tetragon -n kube-system

As a Docker container:

docker run --name tetragon --rm --pull always \
  --pid=host --cgroupns=host --privileged \
  -v /sys/kernel/btf/vmlinux:/var/lib/tetragon/btf \
  quay.io/cilium/tetragon:latest

Monitoring Events

Use the Tetragon CLI (tetra) to monitor events:

kubectl exec -ti -n kube-system ds/tetragon -c tetragon -- tetra getevents -o compact

Example output:

🚀 process /usr/bin/cat /tmp/tetragon
📬 open    /usr/bin/cat /tmp/tetragon
📖 read    /usr/bin/cat /tmp/tetragon 2048 bytes
💥 exit    /usr/bin/cat /tmp/tetragon 0

Performance Considerations

One of Tetragon’s primary advantages is its minimal performance overhead. By operating in the kernel:

Event filtering happens before data reaches user space
No expensive context switches for every event
Selective monitoring reduces CPU and memory usage
In-kernel aggregation minimizes data volume

Benchmarks show Tetragon can handle thousands of events per second with negligible CPU overhead, making it suitable for production environments where performance is critical.

Integration with Security Workflows

Tetragon’s events can be exported to various destinations:

JSON logs: For ingestion into SIEM systems
gRPC API: For real-time processing by security tools
Prometheus metrics: For monitoring and alerting
Falco-compatible format: For teams already using Falco

This flexibility allows Tetragon to integrate seamlessly into existing security operations workflows.

Limitations and Considerations

While powerful, Tetragon has some limitations to consider:

Kernel version requirements: Requires Linux kernel 4.19+ with eBPF support; some features need newer kernels
BTF dependency: Best performance and functionality with kernels that have BTF (BPF Type Format) support
Override action limitations: The Override action requires CONFIG_BPF_KPROBE_OVERRIDE kernel configuration
Learning curve: Writing effective TracingPolicies requires understanding kernel internals and system calls
Privileged access: Requires elevated privileges to load eBPF programs

Comparison with Other Tools

Tetragon vs. Falco:

Both use eBPF (Falco also supports kernel modules)
Tetragon is more focused on enforcement, while Falco is detection-focused
Tetragon has tighter Kubernetes integration
Different rule syntax and policy models

Tetragon vs. Traditional EDR:

EDR tools typically operate in user space with higher overhead
Tetragon provides kernel-level visibility without agents
EDR tools may offer broader OS support beyond Linux
Tetragon excels in containerized/Kubernetes environments

Best Practices

Start with observability: Begin with monitoring-only policies before adding enforcement
Use selectors wisely: Efficient filtering reduces overhead and noise
Test policies in staging: Validate policies don’t cause false positives or break applications
Layer your defenses: Use Tetragon alongside other security controls (network policies, RBAC, etc.)
Monitor Tetragon itself: Track resource usage and event volume
Version control policies: Treat TracingPolicies as code with proper version control
Document your policies: Clearly explain what each policy monitors and why

Future Directions

The Tetragon project continues to evolve with the broader eBPF ecosystem. Upcoming developments include:

Enhanced support for additional architectures
More sophisticated enforcement actions
Improved integration with cloud-native security tools
Enhanced policy templates and libraries
Better visualization and analysis tools

Conclusion

Tetragon represents a significant advancement in cloud-native security by leveraging eBPF to provide deep, kernel-level observability and enforcement with minimal overhead. Its Kubernetes-native design and flexible policy framework make it an excellent choice for security teams looking to enhance their runtime security posture in containerized environments.

Whether you’re concerned about privilege escalation, data exfiltration, or simply want better visibility into what’s happening at the system level, Tetragon provides the tools to observe, detect, and respond to security threats in real-time.

For teams already using Cilium for networking, Tetragon is a natural extension that brings security observability to the same eBPF-powered platform. For others, it offers a compelling standalone solution for runtime security that can scale from development environments to large production clusters.

As the cloud-native security landscape continues to mature, tools like Tetragon that leverage kernel-level capabilities will become increasingly important for maintaining security without sacrificing performance.