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How the parts connect#

This page shows which parts can talk to each other and which are kept apart on purpose. Come back to it whenever you're unsure whether something should be reachable.

Solid arrow = allowed. Dashed arrow ending in × = blocked.

1. Getting into the server#

flowchart TB
  NET(("The internet"))
  WIFI["A device on your<br/>home Wi-Fi"]
  TS["Your devices on Tailscale<br/>(home or away)"]
  subgraph SRV["Home server"]
    SSH["SSH<br/>port 22"]
    SMB["File sharing<br/>port 445"]
    AI["AI model<br/>127.0.0.1:8095"]
  end
  NET -. "router forwards nothing" .-x SRV
  WIFI -- "allowed" --> SSH
  WIFI -. "blocked by firewall" .-x SMB
  TS -- "allowed" --> SSH
  TS -- "allowed" --> SMB
  TS -. "not directly" .-x AI

2. Inside the server#

flowchart TB
  YOU["You, logged in with SSH"]
  subgraph SRV["Home server"]
    AG["Agent system<br/>127.0.0.1:8097<br/>(your account)"]
    subgraph AIACC["'ai' account"]
      AI["AI model<br/>127.0.0.1:8095"]
    end
    SMB["File sharing"]
    F[("/srv/files")]
    B[("/srv/backup")]
  end
  NET(("The internet"))
  YOU -- "SSH tunnel" --> AI
  YOU -- "SSH tunnel" --> AG
  AG -- "asks" --> AI
  SMB --> F
  F -- "nightly backup" --> B
  AI -. "blocked" .-x NET
  AI -. "can't read" .-x F

Who can reach what#

From	To	Allowed?	Why
The internet	anything on the server	No	The router forwards nothing to the server
A device on your home Wi-Fi	SSH (port 22), `.local` name (5353)	Yes	The firewall allows these two (Chapter 12; only from your home network range after Chapter 29)
A device on someone else's network (café, work)	SSH	No (after Chapter 29)	SSH is allowed only from home and Tailscale
A device on your home Wi-Fi	File sharing (445)	No	Not allowed in the firewall. Use Tailscale, or add the optional rule in Chapter 16
Your devices on Tailscale	SSH, file sharing	Yes	Tailscale lets its own traffic through (Chapter 14)
Any other computer, even on Tailscale	AI model, agent system	No	They only listen on `127.0.0.1`, which means "this computer only"
You, through an SSH tunnel	AI model, agent system	Yes	The tunnel makes your request arrive from inside the server (Chapter 23)
Agent system	AI model	Yes	Both are on the same computer
Any other computer	Cockpit dashboard (9090)	No	Listens on `127.0.0.1` only (Chapter 32)
You, through an SSH tunnel	Cockpit dashboard	Yes	Same tunnel method as the AI
Someone guessing SSH logins	SSH	Banned after 5 failures	Fail2ban (Chapter 31)
AI model (the `ai` account)	The internet	No	Blocked by the network guard (Chapter 22)
AI model	Your shared files in `/srv/files`	No	The `ai` account can only read its own model folder
Server	The internet (outgoing)	Yes	Needed for updates and Tailscale
Backup job	`/srv/files` → `/srv/backup`	Yes	Runs nightly as the system (Chapter 17)

What `127.0.0.1` means#

127.0.0.1 (also called localhost or loopback) is every computer's address for itself. A program listening there can't be reached from the network at all, not even from your own Mac. That's why the AI parts use it.

flowchart LR
  subgraph SRV["Server"]
    P["Program on the server"] -- "127.0.0.1:8095" --> M["AI model"]
  end
  O["Any other computer"] -. "127.0.0.1 always means itself" .-x M

The one way in for the AI: an SSH tunnel#

flowchart LR
  B["Browser on your Mac<br/>http://127.0.0.1:18095"] --> T["ssh -L tunnel<br/>(encrypted)"]
  T --> S["Server: arrives<br/>as 127.0.0.1"] --> M["AI model :8095"]

The tunnel only exists while the ssh -L command is running in a terminal window. Close the window and the door closes too. Chapter 23 shows the commands.

Things to remember#

Never add port forwarding on your router. Everything here is designed to work without it.
Docker ignores the firewall. If you run containers later, publish their ports on 127.0.0.1 or the Tailscale address only.
Separate accounts keep parts apart: your user (alex), the system (root) and the AI (ai) can't read each other's private folders.