Kubernetes v1.10
alpha
This page shows how to configure process namespace sharing for a pod. When process namespace sharing is enabled, processes in a container are visible to all other containers in that pod.
You can use this feature to configure cooperating containers, such as a log handler sidecar container, or to troubleshoot container images that don’t include debugging utilities like a shell.
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:
Your Kubernetes server must be version v1.10.
To check the version, enter kubectl version
.
A special alpha feature gate PodShareProcessNamespace
must be set to true
across the system: --feature-gates=PodShareProcessNamespace=true
.
Process Namespace Sharing is enabled using the ShareProcessNamespace
field of
v1.PodSpec
. For example:
share-process-namespace.yaml docs/tasks/configure-pod-container
|
---|
|
Create the pod nginx
on your cluster:
$ kubectl create -f https://k8s.io/docs/tasks/configure-pod-container/share-process-namespace.yaml
Attach to the shell
container and run ps
:
$ kubectl attach -it nginx -c shell
If you don't see a command prompt, try pressing enter.
/ # ps ax
PID USER TIME COMMAND
1 root 0:00 /pause
8 root 0:00 nginx: master process nginx -g daemon off;
14 101 0:00 nginx: worker process
15 root 0:00 sh
21 root 0:00 ps ax
You can signal processes in other containers. For example, send SIGHUP
to
nginx to restart the worker process. This requires the SYS_PTRACE
capability.
/ # kill -HUP 8
/ # ps ax
PID USER TIME COMMAND
1 root 0:00 /pause
8 root 0:00 nginx: master process nginx -g daemon off;
15 root 0:00 sh
22 101 0:00 nginx: worker process
23 root 0:00 ps ax
It’s even possible to access another container image using the
/proc/$pid/root
link.
/ # head /proc/8/root/etc/nginx/nginx.conf
user nginx;
worker_processes 1;
error_log /var/log/nginx/error.log warn;
pid /var/run/nginx.pid;
events {
worker_connections 1024;
Pods share many resources so it makes sense they would also share a process namespace. Some container images may expect to be isolated from other containers, though, so it’s important to understand these differences:
The container process no longer has PID 1. Some container images refuse
to start without PID 1 (for example, containers using systemd
) or run
commands like kill -HUP 1
to signal the container process. In pods with a
shared process namespace, kill -HUP 1
will signal the pod sandbox.
(/pause
in the above example.)
Processes are visible to other containers in the pod. This includes all
information visible in /proc
, such as passwords that were passed as arguments
or environment variables. These are protected only by regular Unix permissions.
Container filesystems are visible to other containers in the pod through the
/proc/$pid/root
link. This makes debugging easier, but it also means
that filesystem secrets are protected only by filesystem permissions.