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Tcpdump of a Kubernetes pod

There are tools like kubectl debug that can start a tcpdump, however I wasn't able to start the tool for multiple pods at the same time. Becauase of an error that happend only sometimes, I needed to get a tcpdump on multiple pods of a deployment.

Example call:
tcpdump -w /proc/1/root/tmp/trace.pcap -i eth0 -nn "src or dst"

-nn doesn't resolve IPs or ports
"src or dst" limits Redis communication

This script gets the host and the container ID of a given pod and then connects to that host, runs tcpdump on it and when stopped using ctrl + c it downloads and deletes the pcap file.

#!/usr/bin/env bash
# Usage:
# bash name-of-pod
remote() {
ssh -i ~/.ssh/k8s_prod_id_rsa -oStrictHostKeyChecking=no -o IdentitiesOnly=yes -o ServerAliveInterval=60 -o ProxyCommand="ssh -W %h:%p -o ServerAliveInterval=60 server" [email protected]$1 $2
remote_cp() {
scp -i ~/.ssh/k8s_prod_id_rsa -o IdentitiesOnly=yes -o ProxyCommand="ssh -W %h:%p server" [email protected]$1:$2 $2
download_pcap() {
remote_cp $hostIP $pod.pcap
remote $hostIP "rm $pod.pcap"
echo "Downloaded to $pod.pcap and removed from server"
exit 0;
trap download_pcap INT
set -ex
hostIP=$(kubectl get pod $pod -o json | jq -r .status.hostIP)
containerID=$(kubectl get pod $pod -o json | jq -r '.status.containerStatuses[] | select(.name == "php") | .containerID' | sed 's/^docker:\/\///g')
interfaceID=$(remote $hostIP "docker exec $containerID /bin/bash -c 'cat /sys/class/net/eth0/iflink'")
eniID=$(remote $hostIP "sudo ip link |grep ^$interfaceID: | sed -nE 's/[0-9]+: (.*)@.*/\1/p'")
remote $hostIP "sudo yum install tcpdump -y"
remote $hostIP "sudo rm -fr $pod.pcap || true"
remote $hostIP "sudo tcpdump -nn 'src or dst' -w $pod.pcap -i $eniID"

#published #kubernetes #tool #script #performance

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© 2021 by Adrian Philipp