Kubectl-debug

中文

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. 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-install them in your production container image.

• demo
• quick start
• build from source
• default image and entrypoints
• future works
• implementation details
• contribute

Demo

Quick Start

kubectl-debug is pretty simple, give it a try!

Install the debug agent DaemonSet in your cluster, which is responsible to run the "new container":

kubectl apply -f https://raw.githubusercontent.com/aylei/kubectl-debug/master/scripts/agent_daemonset.yml

Install the kubectl debug plugin:

# Linux
curl -Lo kubectl-debug https://github.com/aylei/kubectl-debug/releases/download/0.0.1/kubectl-debug_0.0.1_linux-amd64

# MacOS
curl -Lo kubectl-debug https://github.com/aylei/kubectl-debug/releases/download/0.0.1/kubectl-debug_0.0.1_macos-amd64

chmod +x ./kubectl-debug
mv kubectl-debug /usr/local/bin/

For windows user, download the latest binary from the release page and add it to your PATH.

Try it out!

# kubectl 1.12.0 or higher
kubectl debug POD_NAME
# learn more with 
kubectl debug -h

# old versions of kubectl
kubect-debug POD_NAME

Compatibility: I've tested kubectl-debug with kubectl v1.13.1 and kubernetes v1.9.1. I don't have an environment to test more versions but I suppose that kubectl-debug is compatible with all versions of kubernetes and kubectl 1.12.0+. Please file an issue if you find kubectl-debug do not work.

Build from source

Clone this repo and:

# build plugin
go build -o kubectl-debug ./cmd/plugin
# install plugin
mv kubectl-debug /usr/local/bin

# build agent
go build -o debug-agent ./cmd/agent
# build agent image
docker build . -t debug-agent

Default image and entrypoint

kubectl-debug use 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:

agent_port: 10027
image: nicolaka/netshoot:latest
command:
- '/bin/bash'
- '-l'

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).

Future works

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. kubectl-debug runs privileged agent on every node, and client talks to the agent directly. A possible solution is introducing a central apiserver to do RBAC, which integrates to the kube apiserver using aggregation layer
• Protocol. kubectl-debug vendor the SPDY wrapper from client-go. SPDY is deprecated now, websockets maybe a better choice

Details

kubectl-debug consists of 2 components:

• the kubectl plugin: a cli client of node agent, serves kubectl debug command,
• the node agent: responsible for manipulating the "debug container"; node agent will also act as a websockets relay for remote tty

When user run kubectl debug target-pod -c <container-name> /bin/bash:

1. The plugin get the pod info from apiserver and extract the hostIP, if the target container is no existed or not currently running, an error raised.
2. The plugin send a HTTP request to the specific node agent running on the hostIP, which includes a protocol upgrade from HTTP to SPDY.
3. The agent runs a container in the pod's namespaces (ipc, pid, network, etc) with the STDIN stay open (-i flag).
4. The agent checks if the target container is actively running, if not, write an error to client.
5. The agent runs a debug container with tty and stdin opened, the debug contaienr will join the pid, network, ipc and user namespace of the target container.
6. The agent pipes the connection io to the debug contaienr using attach
7. Debug in the debug container.
8. Jobs done, user close the SPDY connection.
9. The node agent close the SPDY connection, then wait the debug contaienr exit and do the cleanup.

Contribute

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