Ubuntu 18.04 LTS is out of support

[cloudchristoph]

Base image for the Router uses Ubuntu 18.04 LTS. This release is out of support and should be updated to Ubuntu 22.04 LTS IMHO.

I'm already working on it w/o breaking backwards compatibility. (also trying Bicep templates):
https://github.com/cloudchristoph/AzureVM-Router/tree/bicep-templates

I would be happy to finish this and create a PR, if you're interested @dmauser.

[dmauser]

Thanks for the heads up! That would be great!