Yifan Gu
91 lines
2.6 KiB
Markdown
91 lines
2.6 KiB
Markdown
---
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---
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The following features either are not supported or have large caveats when using the rkt container runtime.
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##### Non-existent host volume paths
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When mounting a host volume path that does not exist, rkt will error out. Under the Docker runtime, an empty directory will be created at the referenced path.
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An example of a pod which will error out:
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```yaml
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apiVersion: v1
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kind: Pod
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metadata:
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labels:
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name: mount-dne
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name: mount-dne
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spec:
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volumes:
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- name: does-not-exist
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hostPath:
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path: /does/not/exist
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containers:
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- name: exit
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image: busybox
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command: ["sh", "-c", "ls /test; sleep 60"]
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volumeMounts:
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- mountPath: /test
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name: does-not-exist
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```
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##### Kubectl attach
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The `kubectl attach` command does not work under the rkt container runtime.
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And because of this, some flags in `kubectl run` are not supported, including:
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- `--attach=true`
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- `--leave-stdin-open=true`
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- `--rm=true`
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##### Init containers
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The alpha [init container](https://github.com/kubernetes/kubernetes/blob/master/docs/proposals/container-init.md) feature is currently not supported.
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##### Container restart back-off
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Exponential restart back-off for a failing container is currently not supported.
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##### Experimental NVIDIA GPU support
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The `--experimental-nvidia-gpus` flag, and related [GPU features](https://github.com/kubernetes/kubernetes/blob/master/docs/proposals/gpu-support.md) are not supported.
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##### QoS Classes
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Under rkt, QoS classes do not result in the `OOM Score` of containers being adjusted as occurs under Docker.
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##### HostPID and HostIPC namespaces
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Setting a the hostPID or hostIPC flag on a pod is not supported.
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For example, the following pod will not run correctly:
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```yaml
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apiVersion: v1
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kind: Pod
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metadata:
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labels:
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name: host-ipc-pid
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name: host-ipc-pid
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spec:
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hostIPC: true
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hostPID: true
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containers:
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...
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```
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On the other hand, when running the pod with [stage1-fly](https://coreos.com/rkt/docs/latest/running-fly-stage1.html), the pod will be run in the host namespace.
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##### Container image updates (patch)
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Patching a pod to change the image will result in the entire pod restarting, not just the container that was changed.
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##### Volume mounts specifying a subPath
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The [subPath](https://github.com/kubernetes/kubernetes/pull/22575) feature does not work correctly under rkt.
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In addition, the above-issue of Non-existent host volume paths being invalid would make many common use-cases for subPaths fail in that way as well.
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In some cases, this issue can be worked around by creating and using subdirectories from within the container rather than relying on Kubernetes to do so.
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