Why did my server miss urandom warnings due to rate limiting?

These messages are the result of a bug that exhausts the entropy pool on your system. While this pool is typically refilled over time through various actions (such as disk activity, keyboard timings, mouse movements, etc), you can also use a software solution such as haveged.

I just got the error on a brand new system. Can generate like this:

Build a Debian 9 System Image. It will be built with a Grub 2 Kernel.

If you then go and specify the Kernel to be "Latest 64 bit.. (64-linode 124)" Kernel (longer name there). The error will appear at startup.

I have basically simply booted a Linode image then tried to change the Kernel.

I just got the error on a brand new system. Can generate like this:

Build a Debian 9 System Image. It will be built with a Grub 2 Kernel.

If you then go and specify the Kernel to be "Latest 64 bit.. (64-linode 124)" Kernel (longer name there). The error will appear at startup.

I have basically simply made an image then tried to change the Kernel.

This can cause delays in how quickly sshd (and maybe other services) become(s) available after boot.

I second the recommendation already given above to install haveged.