Add kubectl retina debug drop command for real-time packet drop monitoring #1673

Copilot · 2025-06-09T21:16:44Z

This PR implements a new kubectl retina debug drop command that provides real-time monitoring of packet drop events using eBPF, converting the drop debug script functionality into a Go-based CLI subcommand.

Features

Real-time monitoring: Uses the existing dropreason plugin to capture drop events live
Console formatting: Dynamic output formatting with word wrapping to fit terminal width
File output: Optional file writing capability via --output flag
User confirmation: Prompts for confirmation before invasive operations like port-forwarding
IP filtering: Filter events by specific IP addresses using --ips flag
Error handling: Comprehensive error messages for common eBPF permission issues

Usage

# Basic usage - monitor for 30 seconds
kubectl retina debug drop

# Monitor for specific duration and save to file
kubectl retina debug drop --duration=60s --output=drops.log

# Filter by IP addresses
kubectl retina debug drop --ips=10.0.0.1,10.0.0.2

# Skip confirmation prompts
kubectl retina debug drop --confirm=false

Output Format

TIMESTAMP            SRC_IP          DST_IP          PROTO      DROP_REASON          DETAILS
21:30:15.123         10.0.0.1        10.0.0.2        TCP        DROP(42)             Connection refused
21:30:15.456         10.0.0.3        10.0.0.4        UDP        DROP(13)             No route to host

Implementation Details

Command structure: Added debug command group under cli/cmd/debug/
Integration: Leverages existing pkg/plugin/dropreason plugin via event channels
Architecture: Follows established CLI patterns from capture commands
Testing: Comprehensive test coverage for flags, defaults, and functionality
Documentation: Complete documentation in new docs/05-Debug/ section

Requirements

Linux environment with eBPF support
Sufficient privileges for eBPF operations (may require sudo)
Modern kernel version (4.9+)

The command provides helpful error messages when eBPF capabilities are not available, guiding users on common resolution steps.

Fixes #1672.

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Co-authored-by: matmerr <6521405+matmerr@users.noreply.github.com>

kamilprz · 2025-06-19T14:33:42Z

pkg/plugin/dropreason/_cprog/dynamic.h

-// Place holder header file that will be replaced by the actual header file during runtime
-// DO NOT DELETE
+#define ADVANCED_METRICS 1 
+#define BYPASS_LOOKUP_IP_OF_INTEREST 0 


this should not be part of the PR

Fixed in commit 222d88e - reverted the dynamic.h file that was not part of the intended changes.

kamilprz · 2025-06-19T14:35:52Z

cli/cmd/debug/debug.go

+	Long:  "Debug network issues using various Retina debugging tools",
+}
+
+func init() {


There could be some conflicts with the refactor going on at - #1693

kamilprz · 2025-06-19T14:37:11Z

cli/cmd/debug/drop.go

+	dropCmd.Flags().StringVar(&dropOpts.podName, "pod-name", "", "Specific pod name to monitor (optional)")
+	dropCmd.Flags().StringSliceVar(&dropOpts.ips, "ips", nil, "IP addresses to filter for (optional)")
+	dropCmd.Flags().BoolVar(&dropOpts.verbose, "verbose", false, "Enable verbose output")
+	dropCmd.Flags().IntVar(&dropOpts.consoleWidth, "width", 0, "Console width for formatting (auto-detected if 0)")


I don't see a reason to have consoleWidth as a flag. It should always just auto-detect.

Fixed in commit 222d88e - removed the --width flag and made console width auto-detection the only behavior. The consoleWidth is now always automatically detected from the terminal.

kamilprz · 2025-06-19T14:39:06Z

docs/05-Debug/00-overview.md

+
+The `kubectl retina debug drop` command monitors packet drop events in real-time using eBPF technology. This helps network operators and developers quickly identify and troubleshoot packet loss issues.
+
+**Key Features:**


Number of linting errors here. Need to be fixed.

Fixed in commit 222d88e - resolved all markdown linting errors in docs/05-Debug/00-overview.md including missing blank lines around lists, language specification for code blocks, and proper file ending.

kamilprz · 2025-06-19T14:39:28Z

docs/05-Debug/01-cli.md

+
+The command displays drop events in a tabular format:
+
+```


Some linting errors here. Need to be fixed.

Fixed in commit 222d88e - resolved all markdown linting errors in docs/05-Debug/01-cli.md including proper heading formatting, blank lines around code blocks, and language specification.

kamilprz · 2025-06-19T14:46:09Z

cli/cmd/debug/drop.go

+	RunE: runDropCommand,
+}
+
+func init() {


The script under scripts/watch_drops.sh states Poll drop counters on a specific node every INTERVAL seconds (default 30). The go code in this change does not have a configurable interval

Fixed in commit 222d88e - added --interval flag with 1s default to match the configurable interval functionality in watch_drops.sh script. The interval controls the MetricsInterval configuration for the dropreason plugin.

…g, revert dynamic.h Co-authored-by: kamilprz <36544756+kamilprz@users.noreply.github.com>

Initial plan for issue

c36c097

Copilot AI assigned Copilot and matmerr Jun 9, 2025

Copilot started work on behalf of matmerr June 9, 2025 21:16 View session

Copilot AI and others added 2 commits June 9, 2025 21:31

Add debug drop command structure and basic implementation

1fefba5

Co-authored-by: matmerr <6521405+matmerr@users.noreply.github.com>

Complete debug drop command implementation with tests and documentation

1f557ab

Co-authored-by: matmerr <6521405+matmerr@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Krew plugin watching for drop events~~ Add kubectl retina debug drop command for real-time packet drop monitoring Jun 9, 2025

Copilot AI requested a review from matmerr June 9, 2025 21:39

Copilot finished work on behalf of matmerr June 9, 2025 21:39

Merge branch 'main' into copilot/fix-1672

bcc477f

kamilprz reviewed Jun 20, 2025

View reviewed changes

Copilot started work on behalf of kamilprz June 20, 2025 07:54 View session

Address PR feedback: remove width flag, add interval flag, fix lintin…

222d88e

…g, revert dynamic.h Co-authored-by: kamilprz <36544756+kamilprz@users.noreply.github.com>

Copilot AI requested a review from kamilprz June 20, 2025 08:05

Copilot finished work on behalf of kamilprz June 20, 2025 08:05

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		The `kubectl retina debug drop` command monitors packet drop events in real-time using eBPF technology. This helps network operators and developers quickly identify and troubleshoot packet loss issues.

		Key Features:

Add kubectl retina debug drop command for real-time packet drop monitoring #1673

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Features

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Output Format

Implementation Details

Requirements

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