Revise internal system VPN documentation - mermaid diagram

[MariaBego56]

Updated the diagram and text for clarity on VPN setup.

create a mermaid diagram

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[slyon]

Looking at the rendered output in https://canonical-ubuntu-documentation-library--383.com.readthedocs.build/server/how-to/wireguard-vpn/on-an-internal-system/, I cannot see an actual mermaid diagram.

I see the mermaid sources instead:

flowchart LR
  %% ASCII -> Mermaid conversion of: laptop over wlan0 to public untrusted network,
  %% WireGuard wg0 tunnel (10.90.90.1/24 <-> 10.90.90.2/24) to VPN gw and VPN network.

  laptop["Laptop"]

  internet(("public untrusted<br/>network/internet"))
  vpngw["VPN gw"]
  vpn(("VPN network"))

  %% Physical/normal networking
  laptop --|wlan0|--> internet
  internet --|eth0|--> vpngw

  %% WireGuard VPN endpoints
  laptop -. "wg0 10.90.90.1/24" .-> vpn
  vpngw  -. "wg0 10.90.90.2/24" .-> vpn

I'm unclear if this is expected, but would assume that we should be seeing rendered diagrams in the staging environment. Please correct me if that's wrong @s-makin
When pasting that source to something like https://mermaid.live it renders correctly, so seems to be an issue with our docs/environment specifically.

Besides that, the new diagram seems to be loosing information, such as the structure of the home network or the network's IP range, which was 10.10.10.0/24 before, but the tunnel is now using 10.90.90.0/24. In the explanation around the diagram we're referencing those specific IPs from the old diagram, which are now not visible anymore.

[s-makin]

Suggested change

	```mermaid
	```{mermaid}

[s-makin]

This should fix the rendering issue :)

[s-makin]

I'm unclear if this is expected, but would assume that we should be seeing rendered diagrams in the staging environment. Please correct me if that's wrong @s-makin When pasting that source to something like https://mermaid.live it renders correctly, so seems to be an issue with our docs/environment specifically.

Thanks @slyon - Sphinx is sometimes a bit fiddly about recognizing mermaid environments. When declaring a mermaid diagram, you have to wrap mermaid in squiggly brackets (like {mermaid}) otherwise Sphinx tries to treat it like a regular code block. I've added a suggestion to the page which, when applied, should fix the issue and the diagram should render properly after that :)

[s-makin]

Hi @MariaBego56 and thanks for all your work on these diagrams!

I think I identified the reason why the diagrams aren't showing properly, and based on my local testing if you accept the suggestions I left below, and then commit them, it should fix the issue :)

[MariaBego56]

Hi @s-makin ! Thank you very much 😁 I will follow your suggestions and try to male tge changes @slyon requested. I won't have any time to do it before the weekend. I hope that's ok. Have a lovely evening. 😁

[s-makin]

Hi @s-makin ! Thank you very much 😁 I will follow your suggestions and try to male tge changes @slyon requested. I won't have any time to do it before the weekend. I hope that's ok. Have a lovely evening. 😁

That's completely fine, there's no time limit :) let me know if you run into any problems