Kubectl-debug

Overview

kubectl-debug is an out-of-tree solution for troubleshooting running pods, which allows you to run a new container in running pods for debugging purpose (examples). The new container will join the pid, network, user and ipc namespaces of the target container, so you can use arbitrary trouble-shooting tools without pre-installing them in your production container image.

Kubectl-debug
Overview
Screenshots
Quick Start
Build from source
port-forward mode And agentless mode(Default opening)
Configuration
Authorization
Roadmap
Contribute
Acknowledgement

Screenshots

Quick Start

Install the kubectl debug plugin

Homebrew:

brew install aylei/tap/kubectl-debug

Download the binary:

export PLUGIN_VERSION=0.1.1
# linux x86_64
curl -Lo kubectl-debug.tar.gz https://github.com/aylei/kubectl-debug/releases/download/v${PLUGIN_VERSION}/kubectl-debug_${PLUGIN_VERSION}_linux_amd64.tar.gz
# macos
curl -Lo kubectl-debug.tar.gz https://github.com/aylei/kubectl-debug/releases/download/v${PLUGIN_VERSION}/kubectl-debug_${PLUGIN_VERSION}_darwin_amd64.tar.gz

tar -zxvf kubectl-debug.tar.gz kubectl-debug
sudo mv kubectl-debug /usr/local/bin/

For windows users, download the latest archive from the release page, decompress the package and add it to your PATH.

(Optional) Install the debug agent DaemonSet

kubectl-debug requires an agent pod to communicate with the container runtime. In the agentless mode, the agent pod can be created when a debug session starts and to be cleaned up when the session ends.(Turn on agentless mode by default)

While convenient, creating pod before debugging can be time consuming. You can install the debug agent DaemonSet and use --agentless=false params in advance to skip this:

# if your kubernetes version is v1.16 or newer
kubectl apply -f https://raw.githubusercontent.com/aylei/kubectl-debug/master/scripts/agent_daemonset.yml
# if your kubernetes is old version(<v1.16), you should change the apiVersion to extensions/v1beta1, As follows
wget https://raw.githubusercontent.com/aylei/kubectl-debug/master/scripts/agent_daemonset.yml
sed -i '' '1s/apps\/v1/extensions\/v1beta1/g' agent_daemonset.yml
kubectl apply -f agent_daemonset.yml
# or using helm
helm install kubectl-debug -n=debug-agent ./contrib/helm/kubectl-debug
# use daemonset agent mode(close agentless mode)
kubectl debug --agentless=false POD_NAME

Debug instructions

Try it out!

# kubectl 1.12.0 or higher
kubectl debug -h
# if you installed the debug agent's daemonset, you can use --agentless=false to speed up the startup.
# the default agentless mode will be used in following commands
kubectl debug POD_NAME

# in case of your pod stuck in `CrashLoopBackoff` state and cannot be connected to,
# you can fork a new pod and diagnose the problem in the forked pod
kubectl debug POD_NAME --fork

# in fork mode, if you want the copied pod retains the labels of the original pod, you can use the --fork-pod-retain-labels parameter to set(comma separated, and spaces are not allowed)
# Example is as follows
# If not set, this parameter is empty by default (Means that any labels of the original pod are not retained, and the labels of the copied pods are empty.)
kubectl debug POD_NAME --fork --fork-pod-retain-labels=<labelKeyA>,<labelKeyB>,<labelKeyC>

# in order to enable node without public IP or direct access (firewall and other reasons) to access, port-forward mode is enabled by default.
# if you don't need to turn on port-forward mode, you can use --port-forward false to turn off it.
kubectl debug POD_NAME --port-forward=false --agentless=false --daemonset-ns=kube-system --daemonset-name=debug-agent

# old versions of kubectl cannot discover plugins, you may execute the binary directly
kubectl-debug POD_NAME

# use primary docker registry, set registry kubernets secret to pull image
# the default registry-secret-name is kubectl-debug-registry-secret, the default namespace is default
# please set the secret data source as {Username: <username>, Password: <password>}
kubectl-debug POD_NAME --image calmkart/netshoot:latest --registry-secret-name <k8s_secret_name> --registry-secret-namespace <namespace>
# in default agentless mode, you can set the agent pod's resource limits/requests, for example:
# default is not set
kubectl-debug POD_NAME --agent-pod-cpu-requests=250m --agent-pod-cpu-limits=500m --agent-pod-memory-requests=200Mi --agent-pod-memory-limits=500Mi

Example:

# how to create a private docker registry secret
# take the user name 'calmkart' password 'calmkart' as an example
# refer to the official kubernetes documentation for more ways to create
# https://kubernetes.io/docs/concepts/configuration/secret/
echo -n '{Username: calmkart, Password: calmkart}' > ./registrySecret.txt
kubectl create secret generic kubectl-debug-registry-secret --from-file=./registrySecret.txt

You can configure the default arguments to simplify usage, refer to Configuration
Refer to Examples for practical debugging examples

Build from source

Clone this repo and:

# make will build plugin binary and debug-agent image
make
# install plugin
mv kubectl-debug /usr/local/bin

# build plugin only
make plugin
# build agent only
make agent-docker

port-forward mode And agentless mode(Default opening)

port-foward mode: By default, kubectl-debug will directly connect with the target host. When kubectl-debug cannot connect to targetHost:agentPort, you can enable port-forward mode. In port-forward mode, the local machine listens on localhost:agentPort and forwards data to/from targetPod:agentPort.
agentless mode: By default, debug-agent needs to be pre-deployed on each node of the cluster, which consumes cluster resources all the time. Unfortunately, debugging Pod is a low-frequency operation. To avoid loss of cluster resources, the agentless mode has been added in #31. In agentless mode, kubectl-debug will first start debug-agent on the host where the target Pod is located, and then debug-agent starts the debug container. After the user exits, kubectl-debug will delete the debug container and kubectl-debug will delete the debug-agent pod at last.

Configuration

kubectl-debug uses nicolaka/netshoot as the default image to run debug container, and use bash as default entrypoint.

You can override the default image and entrypoint with cli flag, or even better, with config file ~/.kube/debug-config:

# debug agent listening port(outside container)
# default to 10027
agentPort: 10027

# whether using agentless mode
# default to true
agentless: true
# namespace of debug-agent pod, used in agentless mode
# default to 'default'
agentPodNamespace: default
# prefix of debug-agent pod, used in agentless mode
# default to  'debug-agent-pod'
agentPodNamePrefix: debug-agent-pod
# image of debug-agent pod, used in agentless mode
# default to 'aylei/debug-agent:latest'
agentImage: aylei/debug-agent:latest

# daemonset name of the debug-agent, used in port-forward
# default to 'debug-agent'
debugAgentDaemonset: debug-agent
# daemonset namespace of the debug-agent, used in port-forwad
# default to 'default'
debugAgentNamespace: kube-system
# whether using port-forward when connecting debug-agent
# default true
portForward: true
# image of the debug container
# default as showed
image: nicolaka/netshoot:latest
# start command of the debug container
# default ['bash']
command:
- '/bin/bash'
- '-l'
# private docker registry auth kuberntes secret
# default RegistrySecretName is kubectl-debug-registry-secret
# default namspace is default
RegistrySecretName: my-debug-secret
RegistrySecretNamespace: debug
# in agentless mode, you can set the agent pod's resource limits/requests:
# default is not set
agentCpuRequests: ""
agentCpuLimits: ""
agentMemoryRequests: ""
agentMemoryLimits: ""
# in fork mode, if you want the copied pod retains the labels of the original pod, you can change this params
# format is []string
# If not set, this parameter is empty by default (Means that any labels of the original pod are not retained, and the labels of the copied pods are empty.)
forkPodRetainLabels: []

If the debug-agent is not accessible from host port, it is recommended to set portForward: true to using port-forawrd mode.

PS: kubectl-debug will always override the entrypoint of the container, which is by design to avoid users running an unwanted service by mistake(of course you can always do this explicitly).

Authorization

Currently, kubectl-debug reuse the privilege of the pod/exec sub resource to do authorization, which means that it has the same privilege requirements with the kubectl exec command.

Roadmap

kubectl-debug is supposed to be just a troubleshooting helper, and is going be replaced by the native kubectl debug command when this proposal is implemented and merged in the future kubernetes release. But for now, there is still some works to do to improve kubectl-debug.

Security: currently, kubectl-debug do authorization in the client-side, which should be moved to the server-side (debug-agent)
More unit tests
More real world debugging example
e2e tests

If you are interested in any of the above features, please file an issue to avoid potential duplication.

Contribute

Feel free to open issues and pull requests. Any feedback is highly appreciated!

Acknowledgement

This project would not be here without the effort of our contributors, thanks!

fit2cloudrd / kubectl-debug