PLEASE NOTE: This document applies to the HEAD of the source tree
If you are using a released version of Kubernetes, you should
refer to the docs that go with that version.
Documentation for other releases can be found at
[releases.k8s.io](http://releases.k8s.io).
--
# Notes on Different UX with rkt container runtime
### Doesn't support ENTRYPOINT + CMD feature
To run a Docker image, rkt will convert it into [App Container Image (ACI) format](https://github.com/appc/spec/blob/master/SPEC.md) first.
However, during the conversion, the `ENTRYPOINT` and `CMD` are concatentated to construct ACI's `Exec` field.
This means after the conversion, we are not able to replace only `ENTRYPOINT` or `CMD` without touching the other part.
So for now, users are recommended to specify the **executable path** in `Command` and **arguments** in `Args`.
(This has the same effect if users specify the **executable path + arguments** in `Command` or `Args` alone).
For example:
```yaml
apiVersion: v1
kind: Pod
metadata:
name: nginx
labels:
name: nginx
spec:
containers:
- name: nginx
image: nginx
ports:
- containerPort: 80
```
The above pod yaml file is valid as it's not specifying `Command` or `Args`, so the default `ENTRYPOINT` and `CMD` of the image will be used.
```yaml
apiVersion: v1
kind: Pod
metadata:
name: busybox
labels:
name: busybox
spec:
containers:
- name: busybox
image: busybox
command:
- /bin/sleep
- 1000
```
```yaml
apiVersion: v1
kind: Pod
metadata:
name: busybox
labels:
name: busybox
spec:
containers:
- name: busybox
image: busybox
command:
- /bin/sleep
args:
- 1000
```
```yaml
apiVersion: v1
kind: Pod
metadata:
name: busybox
labels:
name: busybox
spec:
containers:
- name: busybox
image: busybox
args:
- /bin/sleep
- 1000
```
All the three examples above are valid as they contain both the executable path and the arguments.
```yaml
apiVersion: v1
kind: Pod
metadata:
name: busybox
labels:
name: busybox
spec:
containers:
- name: busybox
image: busybox
args:
- 1000
```
The last example is invalid, as we cannot override just the `CMD` of the image alone.
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