r/linux_virtual_machine: support for parsing ssh2 keys

[AleFazio]

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Description

Good morning,

We have an infrastructure generated in Azure which we are trying to terraform.
In particular, we have a problem with admin_ssh_key "public_key" in "azurerm_linux_virtual_machine" when the key imported is in the following format:
---- BEGIN SSH2 PUBLIC KEY ----
Comment: "rsa-key-20200715"
ssh-rsa AAA....
---- END SSH2 PUBLIC KEY --

We have several virtual machines with their linked ssh key in different format and we reference to them using the file function:

admin_ssh_key {
username = "azureuser"
public_key = file(<path_to_ssh_key>)
}

After performing the command terraform plan, it manages to compare information with keys in string format but not in the ---- BEGIN SSH2 PUBLIC KEY ---- format.

I tried using file either with or without .pub extension but I didn't get any result.
Below a screenshot of the error:

I also tried using an input key even in the ssh-rsa common format (ignoring the 'BEGIN/END' and 'comment' keyword) but Terraform tries to forces replacement in this case.

Terraform (and AzureRM Provider) Version

Versions:
Terraform v0.13.2
Provider azurerm: 2.82.0

Affected Resource(s)

azurerm_linux_virtual_machine

Expected Behaviour

The input key should be correctly decoded and matched with the one imported along with the vm configuration in the state file

Actual Behaviour

Decoding error (Error: Error decoding "admin_ssh_key.0.public_key" for public key data) when running terraform plan/apply

Steps to Reproduce

1. Get your key in the following format:
   '---- BEGIN SSH2 PUBLIC KEY ----
   Comment: "rsa-key-20200715"
   ssh-rsa AAA....
   ---- END SSH2 PUBLIC KEY --'
2. Copy/paste the key in a file (or just use the original key file if you have it) and refer to it using file(path) function (public_key field).
3. run terraform plan/apply

References

In #9238 I mentioned this issue along with the 'forces replacement' issue (when the key is created through the portal) since I thought they could be related to the same problem but unfortunately they're not.

[CruzanCaramele]

@AleFazio hello, please did you find a solution yet, i am having the same problem as well

[balintbako]

I have the same issue in v2.99 azure provider

It seems to be fine if the file format is as per Linux ssh-keygen, i.e. a single line like this:
ssh-rsa AAA....

[karthikvenkat17]

Hi, Are there any workarounds for this issue to avoid terraform forcing replacement when importing existing virtual machines which has public key in this format
'---- BEGIN SSH2 PUBLIC KEY ----
Comment: "rsa-key-20200115"
ssh-rsa AAA....
---- END SSH2 PUBLIC KEY --'

[AleFazio]

Indeed, it’s unbelievable Microsoft hasn’t fixed this yet