Openshift Node Kernel

OpenShift Node Kernel Inspection Skill

This skill provides utilities for inspecting kernel-level networking configuration on OpenShift/Kubernetes nodes using oc debug.

Overview

The skill enables interaction with kernel networking tools on Kubernetes nodes without requiring SSH access. It uses oc debug to create ephemeral containers with host network access and executes kernel commands in the host's namespace.

Commands Provided

node-kernel-ip

Executes ip commands to inspect routing tables, network devices, and interfaces.

Script: node-kernel-ip.sh

Usage:

./node-kernel-ip.sh <node> <image> --command <cmd> [--options <opts>] [--filter <params>]

Example:

./node-kernel-ip.sh worker-1 registry.redhat.io/rhel9/support-tools --command "route show"

node-kernel-iptables

Executes iptables or ip6tables commands to inspect packet filter rules.

Script: node-kernel-iptables.sh

Usage:

./node-kernel-iptables.sh <node> <image> --command <cmd> [--table <table>] [--filter <params>]

Example:

./node-kernel-iptables.sh worker-1 registry.redhat.io/rhel9/support-tools --command "-L POSTROUTING" --table nat --filter "-nv4"

node-kernel-nft

Executes nft commands to inspect nftables packet filtering and classification rules.

Script: node-kernel-nft.sh

Usage:

./node-kernel-nft.sh <node> <image> --command <cmd> [--family <family>]

Example:

./node-kernel-nft.sh worker-1 registry.redhat.io/rhel9/support-tools --command "list tables" --family inet

node-kernel-conntrack

Executes conntrack commands or reads /proc/net/nf_conntrack to inspect connection tracking entries.

Script: node-kernel-conntrack.sh

Usage:

./node-kernel-conntrack.sh <node> <image> [--command <cmd>] [--filter <params>]

Example:

./node-kernel-conntrack.sh worker-1 registry.redhat.io/rhel9/support-tools --command "-L" --filter "-s 1.2.3.4"

Helper Functions

The kernel-helper.sh script provides shared functions:

• check_utility_exists: Verifies a utility exists in the debug image
• execute_kernel_command: Executes commands on a node via oc debug
• filter_warnings: Removes common oc debug warning messages from output
• validate_node_exists: Validates node name exists in cluster
• detect_and_set_kubeconfig: Auto-detects and configures kubeconfig

Output Handling

All commands ensure:

• stdout contains only the actual command output (routing tables, interface info, etc.)
• stderr contains warnings, debug messages, and errors
• Common oc debug warnings are filtered out automatically using improved regex patterns
• Output is explicitly captured and returned to ensure proper data flow to calling processes

Improvements

The execute_kernel_command() function explicitly captures all output from oc debug and filters warnings before returning results, ensuring:

1. Complete output capture: All stdout/stderr is captured in a variable
2. Reliable filtering: Uses single grep -E with multiple patterns for efficiency
3. Guaranteed output: The || cat fallback ensures output passes through even if no warnings are found
4. Explicit return: Output is explicitly sent to stdout using printf for reliable data flow