Aks-engine: Multiple SSH keys in linuxProfile

[UncleTawnos]

Is this a request for help?:

YES

---

Is this an ISSUE or FEATURE REQUEST? (choose one):

ISSUE

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What version of aks-engine?:

v0.30

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Kubernetes version:
1.13.3

What happened:
Adding multiple SSH keys results in validation error
FATA[0000] error loading API model in generateCmd: error parsing the api model: Namespace Properties.LinuxProfile.SSH.PublicKeys is not caught, Key: 'Properties.LinuxProfile.SSH.PublicKeys' Error:Field validation for 'PublicKeys' failed on the 'len' tag

What you expected to happen:
multiple keys added to user profile

How to reproduce it (as minimally and precisely as possible):

try to generate templates from following linuxProfile

    "linuxProfile": {
      "adminUsername": "tech",
      "ssh": {
        "publicKeys": [
          {
            "keyData": "ssh-rsa key1"
          },
          {
            "keyData": "ssh-rsa key2"
          }
        ]
      }

[UncleTawnos]

https://github.com/Azure/aks-engine/blob/b1ffc7545cfedb759763d0a0c2bb44507cab8ff9/pkg/api/vlabs/types.go#L137 there is the limitation

[PatrickLang]

This is definitely supported for Linux VMs configured through an ARM template https://docs.microsoft.com/en-us/rest/api/compute/virtualmachines/createorupdate#sshpublickey

In addition to the typecheck, this template parameter needs to change:
https://github.com/Azure/aks-engine/blob/master/pkg/engine/params.go#L81

and the templates that refer to it:
https://github.com/Azure/aks-engine/blob/master/parts/k8s/kubernetesmasterresources.t#L866
https://github.com/Azure/aks-engine/blob/master/parts/k8s/kubernetesagentresourcesvmss.t#L122
https://github.com/Azure/aks-engine/blob/master/parts/k8s/kubernetesagentresourcesvmas.t#L186

[PatrickLang]

also
https://github.com/Azure/aks-engine/blob/master/parts/k8s/kuberneteswindowssetup.ps1#L250
https://github.com/Azure/aks-engine/blob/master/parts/k8s/windowsinstallopensshfunc.ps1#L30

to support Windows