126 lines
3.5 KiB
Markdown
126 lines
3.5 KiB
Markdown
---
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title: Share Process Namespace between Containers in a Pod
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min-kubernetes-server-version: v1.10
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reviewers:
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- verb
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- yujuhong
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- dchen1107
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content_template: templates/task
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weight: 160
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---
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{{% capture overview %}}
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{{< feature-state state="beta" >}}
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This page shows how to configure process namespace sharing for a pod. When
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process namespace sharing is enabled, processes in a container are visible
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to all other containers in that pod.
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You can use this feature to configure cooperating containers, such as a log
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handler sidecar container, or to troubleshoot container images that don't
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include debugging utilities like a shell.
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{{% /capture %}}
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{{% capture prerequisites %}}
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{{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
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Process Namespace Sharing is a **beta** feature that is enabled by default. It
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may be disabled by setting `--feature-gates=PodShareProcessNamespace=false`.
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{{% /capture %}}
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{{% capture steps %}}
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## Configure a Pod
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Process Namespace Sharing is enabled using the `ShareProcessNamespace` field of
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`v1.PodSpec`. For example:
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{{< codenew file="pods/share-process-namespace.yaml" >}}
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1. Create the pod `nginx` on your cluster:
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```shell
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kubectl apply -f https://k8s.io/examples/pods/share-process-namespace.yaml
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```
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1. Attach to the `shell` container and run `ps`:
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```shell
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kubectl attach -it nginx -c shell
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```
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If you don't see a command prompt, try pressing enter.
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```
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/ # ps ax
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PID USER TIME COMMAND
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1 root 0:00 /pause
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8 root 0:00 nginx: master process nginx -g daemon off;
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14 101 0:00 nginx: worker process
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15 root 0:00 sh
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21 root 0:00 ps ax
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```
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You can signal processes in other containers. For example, send `SIGHUP` to
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nginx to restart the worker process. This requires the `SYS_PTRACE` capability.
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```
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/ # kill -HUP 8
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/ # ps ax
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PID USER TIME COMMAND
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1 root 0:00 /pause
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8 root 0:00 nginx: master process nginx -g daemon off;
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15 root 0:00 sh
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22 101 0:00 nginx: worker process
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23 root 0:00 ps ax
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```
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It's even possible to access another container image using the
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`/proc/$pid/root` link.
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```
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/ # head /proc/8/root/etc/nginx/nginx.conf
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user nginx;
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worker_processes 1;
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error_log /var/log/nginx/error.log warn;
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pid /var/run/nginx.pid;
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events {
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worker_connections 1024;
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```
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{{% /capture %}}
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{{% capture discussion %}}
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## Understanding Process Namespace Sharing
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Pods share many resources so it makes sense they would also share a process
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namespace. Some container images may expect to be isolated from other
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containers, though, so it's important to understand these differences:
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1. **The container process no longer has PID 1.** Some container images refuse
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to start without PID 1 (for example, containers using `systemd`) or run
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commands like `kill -HUP 1` to signal the container process. In pods with a
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shared process namespace, `kill -HUP 1` will signal the pod sandbox.
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(`/pause` in the above example.)
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1. **Processes are visible to other containers in the pod.** This includes all
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information visible in `/proc`, such as passwords that were passed as arguments
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or environment variables. These are protected only by regular Unix permissions.
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1. **Container filesystems are visible to other containers in the pod through the
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`/proc/$pid/root` link.** This makes debugging easier, but it also means
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that filesystem secrets are protected only by filesystem permissions.
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{{% /capture %}}
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