fix: the web service listens on the internal address, the external address or both.

ADR.md

@@ -27,28 +27,33 @@ port is reachable from the external interface only when it is in `exposed_ports`
 in `DOCKER-USER` are not touched, because the package owns only its own chain. Restarting Docker
 restores the rules. The rules cover IPv4 only.
 
-## ADR-2: A small status web service, bound to the internal address
+## ADR-2: A small status web service, on the interfaces web.listen chooses
 
 Status: Accepted
 
 Context: The router has no way to see its state without a shell. A check from the protected
-network, by a person or by a monitor, needs a page or an endpoint. The router is an
-internet-facing host, so what the service shows and where it listens matter.
+network, by a person or by a monitor, needs a page or an endpoint, and so does the platform that
+deploys the router, which reaches it on its public address. The router is an internet-facing
+host, so what the service shows and where it listens matter.
 
 Decision: The `vpn-router-web` unit runs one Python script on the standard library's
 `http.server`, with the package's own modules and the Python packages of the Ubuntu archive that
-the package depends on, and no web framework. It listens on the address of the internal interface and on
-`web.port`, 7081 by default, and is on unless `web.enabled` is `false` (ADR-7). `/` is for
-people, in plain text for `curl` and `wget` and as a Tailwind CSS page for a browser, and
-`/status` is the same status as JSON. It shows the state of the services, the package version
-and the state of the site-to-site, road-warrior, OpenVPN and WireGuard features, and nothing from
-the configuration. `vpn-router-setup` opens the port on the internal interface in UFW and writes
-the features and the facts it resolves to `/run/vpn-router/web.json`.
+the package depends on, and no web framework. It listens on `web.port`, 7081 by default, on the
+address of the internal interface, of the external interface or of both, as `web.listen` sets
+(`internal`, `external` or `both`, the default), with a server for each address, and is on
+unless `web.enabled` is `false` (ADR-7). `/` is for people, in plain text for `curl` and `wget`
+and as a Tailwind CSS page for a browser, and `/status` is the same status as JSON. It shows the
+state of the services, the package version and the state of the site-to-site, road-warrior,
+OpenVPN and WireGuard features, and nothing from the configuration. `vpn-router-setup` opens the
+port on both interfaces in UFW, so the choice of `web.listen` is made by the service alone, and
+writes the features and the facts it resolves to `/run/vpn-router/web.json`.
 
-Consequences: Nothing outside the internal network can reach it, since it listens on the internal
-address only and the firewall opens the port on the internal interface only. `/` and `/status`
-have no authentication, which is acceptable because they are read only and show no
-configuration. It runs as root, because `swanctl` and `wg` need it, with `NoNewPrivileges`,
+Consequences: By default the service is reachable from the internet on the external address;
+`web.listen` set to `internal` keeps it to the internal network. It serves plain HTTP, so the
+passwords of `/auth` and the tokens cross the internet unencrypted. A change of `web.listen`
+needs no run of setup, since the firewall does not depend on it; the package's upgrade runs
+setup, which writes the rules. `/` and `/status` have no authentication, which is acceptable because they are
+read only and show no configuration. It runs as root, because `swanctl` and `wg` need it, with `NoNewPrivileges`,
 `ProtectSystem=strict`, `ProtectHome` and `PrivateTmp`. The Tailwind style comes from a CDN, so a
 browser on a network without internet shows the unstyled page, and `curl` is unaffected.
 
@@ -60,7 +65,7 @@ Context: Clients such as the Router Manager, and people with `curl`, need the co
 the users and the groups of the router, which `/` and `/status` must not show. Both people and
 programs sign in with a user of the directory. A secret shared with the platform that deploys
 the router would let whoever holds it, and every copy of the deployment's state, make tokens.
-The service listens on plain HTTP on the internal network.
+The service listens on plain HTTP.
 
 Decision: `/config`, `/users` and `/groups` need a JWT in an `Authorization: Bearer` header,
 HS256, verified with `hmac` and `hashlib`; no other algorithm is accepted. The key is
@@ -158,22 +163,23 @@ and the holders of an admin token manage users.
 Status: Accepted
 
 Context: The status page is the tool to see a problem of `vpn-router-setup`, so it must run
-whatever state setup is in, also before setup has run and while it fails. The internal address,
-`web.port` and `web.enabled` can change at any time.
+whatever state setup is in, also before setup has run and while it fails. The addresses,
+`web.listen`, `web.port` and `web.enabled` can change at any time.
 
 Decision: The service depends on nothing to start and does not end on its own. A discovery
-thread works out, every 30 seconds, the internal address from `vpn-router.json` as
-`general.mode` directs, with the discovery code in `vpnrouter_net.py`, which `vpnrouter.py` uses
-too, and `web.port` and `web.enabled` from the same file. It runs the HTTP server in a thread of
-its own at that address and port, stops it and starts a new one when they change, and runs none
-while the service is disabled, the address is not known or it cannot be bound. Each request
+thread works out, every 30 seconds, the addresses of the interfaces `web.listen` names from
+`vpn-router.json` as `general.mode` directs, with the discovery code in `vpnrouter_net.py`,
+which `vpnrouter.py` uses too, and `web.port` and `web.enabled` from the same file. It runs an
+HTTP server in a thread of its own at each address and the port, stops one and starts a new one
+when they change, and runs none while the service is disabled or no address is known; an address
+that cannot be bound is tried again the next round. Each request
 reads the signing key and `vpn-router.json`, and the features and resolved facts from
 `web.json`, which setup writes when it applies the configuration, so the service shows what setup
 applied; while that file is missing the router shows no features. The unit is not
 ordered after `vpn-router-setup`, and setup does not restart it.
 
-Consequences: The status page answers as soon as the internal address exists, whatever state
-setup is in, and follows a changed address, port or `web.enabled` within 30 seconds without a
+Consequences: The status page answers as soon as an address exists, whatever state setup is in,
+and follows a changed address, `web.listen`, port or `web.enabled` within 30 seconds without a
 restart. A new signing key applies to the next request. The interfaces are read every 30
 seconds, which costs a few `ip` commands.
 
@@ -209,9 +215,9 @@ router's `/auth`, keeps their tokens in a server-side session in PostgreSQL behi
 session's access token, refreshing it as needed; it holds no logic of the router's own and no
 key of it. It reads its settings from `/etc/vpn-router-manager/manager.json` at each request; on
 the router the settings not given come from `vpn-router.json`, and it listens on the internal
-address like the status web service, with the same discovery thread. `vpn-router-setup` opens
-the manager's port on the internal interface while the manager is installed, so the firewall
-stays in one place.
+address, the external address or both, as its own `listen` sets, like the status web service,
+with the same discovery thread. `vpn-router-setup` opens the manager's port on the internal and
+the external interface while the manager is installed, so the firewall stays in one place.
 
 Consequences: The router needs no Node.js; the package needs only `python3` and packages of the
 Ubuntu archive. Tokens never reach the browser, and sessions survive a restart of the manager.
@@ -320,8 +326,8 @@ within 15 minutes; a successful bind clears the count; `vpn-router-user unlock`
 `/auth` answers the same 401 for a wrong name, password or code and for a locked or disabled
 user. `/auth` and `/auth/refresh` allow 10 calls a minute per client address, counted in memory,
 and answer 429 with `Retry-After` beyond that. The client address is the peer, or the last
-`X-Forwarded-For` entry for a peer in `web.trusted_proxies`, by default the address the service
-listens on, where a manager on the router calls from.
+`X-Forwarded-For` entry for a peer in `web.trusted_proxies`, by default the address the call came
+in on, which is the address a manager on the router calls from.
 
 Consequences: One lockout covers OpenVPN and `/auth`, kept by slapd alone. Someone who knows a
 user name can lock the user out for 15 minutes at a time. The rate limit restarts with the