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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.

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.

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:

curl 

Try it out!

kubectl debug POD_NAME
# learn more with 
kubectl debug -h

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

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).

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.

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