linux-cloud-router/ADR.md

Architecture Decision Records

ADR-1: Docker's published ports are filtered in DOCKER-USER by the package

Status: Accepted

Context: Docker adds its own iptables rules for published ports. They are evaluated before UFW's, so a published port is reachable from the external interface whatever UFW says. Docker reserves the DOCKER-USER chain, evaluated first in FORWARD, for rules of the operator. The router is an internet-facing host, and Docker is installed on it for services run alongside the router.

Decision: The package secures Docker itself. A docker configuration section has mode (auto, on, off) and exposed_ports. In auto mode the rules are applied when docker.service is installed, which is what the package looks up; on requires Docker and off removes the rules. The rules are in a chain of their own, VPN-ROUTER-DOCKER, entered by one jump at the top of DOCKER-USER. For traffic from the external interface they accept IPsec protected traffic, TCP to exposed_ports and established connections, and drop the rest. The vpn-router-docker unit applies them after docker.service starts and removes them when it stops; vpn-router-setup restarts it while Docker runs.

Consequences: Installing Docker first is recommended; auto mode then finds it as soon as the package is configured. When Docker is installed after the package, the rules are applied by restarting vpn-router-setup, a reboot or a restart of Docker, not by Docker's first start, because vpn-router-docker is already active. A published port is reachable from the external interface only when it is in exposed_ports. Other rules 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

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.

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.

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, 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.

ADR-3: The protected paths take JWTs that only the router signs

Status: Accepted

Context: Clients such as the Router Manager, and people with curl, need the configuration, 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.

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 /etc/vpn-router/web.key, random, made by vpn-router-setup on the router and readable by root only; it is never configured or output, and web.jwt_secret is ignored. The router itself issues the tokens: POST /auth checks a user's password and TOTP code with a bind (ADR-14) and answers an access token naming the user in sub, valid for 5 minutes, and a refresh token valid for 8 hours (ADR-15); vpn-router-token makes tokens with the admin claim (ADR-13). A token without admin must expire within ten minutes, so a leaked one is of little use. Without the key the paths and /auth are not served. The configuration shown has no secret options (ADR-8).

Consequences: Nothing outside the router can make a token, so a token is either issued to a user who signed in or made by root on the router. A client keeps the refresh token to stay signed in. A token of vpn-router-token can be revoked only by replacing the key, which ends every token. Tokens, passwords and answers cross the network unencrypted, so the API is for a trusted internal network; HTTPS would need a certificate that the package does not have.

ADR-4: Users are kept in a local OpenLDAP directory

Status: Accepted

Context: OpenVPN needs user accounts with passwords, and the users are meant to cover every P2S system of the router, including IKEv2 EAP-TLS and WireGuard, which an OIDC provider cannot authenticate. Everything the router runs comes from the Ubuntu archive. slapd, its Python module python3-ldap and the OpenVPN plugin openvpn-auth-ldap are all in the archive; the plugin checks a password by binding as the user, so the hash scheme is slapd's alone. An OIDC provider can read the directory through its LDAP connector.

Decision: The users are entries in slapd. The package keeps its own database, dc=vpn-router,dc=local in /var/lib/ldap/vpn-router (the path the slapd AppArmor profile allows), next to the database the slapd package creates from the host's domain, so the package does not depend on the debconf answers of slapd. Its root DN is root's peer-credential DN on the local socket, so vpn-router-setup manages it with SASL EXTERNAL and no administrator password exists. Users are changed by cn=user-manager,ou=services, whose ACLs allow writing ou=users and setting passwords (=wx) but not reading them. Passwords are hashed with ARGON2, and the ppolicy overlay locks a disabled user (pwdAccountLockedTime, effective with pwdLockout). slapd listens on the local socket only. Provisioning checks every step before changing it, so it runs at every start of vpn-router-setup.

Consequences: The package depends on slapd, python3-ldap, openvpn and openvpn-auth-ldap, and vpn-router-setup and vpn-router-user import python3-ldap. The service account's password is a root-only file. The directory is user data: it is kept on purge, and it is backed up with slapcat, not by copying files.

ADR-5: OpenVPN clients need a certificate and the password of the user it names

Status: Accepted

Context: The router CA issues client certificates for IKEv2. OpenVPN can check a certificate, a password, or both. With both, a certificate alone and a password alone are not enough, but openvpn-auth-ldap checks only the password of the user name given at login, which need not be the user of the certificate.

Decision: OpenVPN checks the certificate against the CA and the CRL, the password with openvpn-auth-ldap, and runs openvpn-same-user as auth-user-pass-verify with via-env, which accepts the login only when the user name equals the certificate's common name. OpenVPN calls both and needs both to pass. A user's certificate has the user name as its common name, is issued when the user is added and revoked when the user is removed. The CRL is created with the CA, so that crl-verify has a file from the start, and is valid for ten years, because the router renews it only when it revokes a certificate. The server uses the router's own certificate, whose common name is wan.local_fqdn; the client profile checks that name (verify-x509-name), since the CA's certificates carry both the server and the client purpose.

Consequences: Disabling a user locks the password, which stops OpenVPN but not IKEv2, which checks certificates only; removing a user revokes the certificate for both. A user's certificate expires after the CA's default of a year and is renewed by removing and adding the user again.

ADR-6: The web service and vpn-router-user share one module for users

Status: Accepted

Context: Users are managed from the command line, by an operator at a terminal, and through /users of the web service, by the Router Manager. Both must apply the same rules to names, passwords and person attributes, and both change the directory and the CA. simple-ca keeps the CA's state in one file, so two changes must not run at the same time. The web unit is sandboxed with ProtectSystem=strict.

Decision: vpnrouter_users.py holds the user operations, the checks and a session that takes a lock and the connection of the user manager account. The web service imports it and maps a Failure to the HTTP status; vpn-router-user imports it and adds the argument parsing and the output, text for people and JSON with --json. The web unit allows writing the paths the operations need: /run/vpn-router for the lock, /etc/vpn-router/pki for the certificates and the CA's state, and /etc/swanctl/x509crl for the published CRL.

Consequences: The rules exist once. A request starts no process, and a password never leaves the process that received it. The web service imports python3-ldap and the package's configuration module. The API is protected by the tokens of ADR-3, so only members of admins and the holders of an admin token manage users.

ADR-7: The web service starts on its own and reads its inputs at each request

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.

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 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 restart. A new signing key applies to the next request. The interfaces are read every 30 seconds, which costs a few ip commands.

ADR-8: /config leaves secret options out

Status: Accepted

Context: A secret has no use outside the router, so a client never needs it, and showing even that a secret is set tells a reader more than it needs.

Decision: The configuration that vpn-router-setup writes for the web service has no secret options at all. They are recognised by name: psk, database, whose connection string may hold a password, and options with secret, password, token or a _key ending in the name.

Consequences: No secret reaches the web service's state file or any answer of the API. A client cannot tell whether a secret is set. A new secret option needs a name that matches.

ADR-9: The Router Manager is a separate package with a small Python server

Status: Accepted

Context: The router needs a web application to manage it, which may run on the router or on another Linux system. The router's web service issues tokens through /auth (ADR-3) and sends no CORS headers, so a browser cannot call it directly, and tokens kept in the page could be read by its scripts.

Decision: vpn-router-manager is a Debian package of its own, built in the repository linux-cloud-router-manager. A React and MUI application in the style of manage-ui is built with Vite when the package is built and shipped as static files. A Python server, using the Ubuntu packages python3-requests and python3-psycopg, serves them, signs users in through the router's /auth, keeps their tokens in a server-side session in PostgreSQL behind an HttpOnly cookie, and passes every other /api/<path> call to the router's /<path> with the 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.

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. The router decides what a user may do; the manager only signs in. The application checks the shape of every answer of the router. The router's firewall depends on whether the manager is installed, and a changed manager port needs vpn-router-setup to run again.

ADR-10: Users and their certificates do not depend on a P2S system being enabled

Status: Accepted

Context: Users are prepared before a P2S system is switched on, and the Router Manager manages them on any configured router, with or without one.

Decision: Once a platform is chosen, vpn-router-setup always provisions the user directory in slapd and the CA with its CRL; the server certificate follows once wan.local_fqdn is set. /users and vpn-router-user rely only on the directory and the CA. Only the OpenVPN client profile needs OpenVPN to be enabled.

Consequences: slapd always holds the directory and the CA always exists on a configured router, even when no P2S system uses them. An operator who wants a CA of their own must place it before choosing the platform.

ADR-11: Groups are groupOfNames entries that never become empty

Status: Accepted

Context: Users are to be organised in groups. Groups record membership only; nothing on the router reads them. LDAP clients that read groups, such as openvpn-auth-ldap and the LDAP connectors of OIDC providers, expect groupOfNames with member DNs, and OpenLDAP's core schema requires a groupOfNames to have at least one member.

Decision: A group is cn=<name>,ou=groups,dc=vpn-router,dc=local, a groupOfNames with the DNs of its members and an optional description. A group is created with at least one member, and taking out its last member is refused; such a group is removed instead. Removing a user takes it out of its groups and is refused while the user is the last member of one. The group operations are in vpnrouter_users.py with the user operations, so they share the session and its lock; vpn-router-group is a tool of its own beside vpn-router-user, and the web service serves them under /groups. Group names follow the rules of user names.

Consequences: A group always satisfies the schema without a placeholder member, and an empty group cannot exist. Removing a user or a member can need another step first. A later use of groups, such as allowing OpenVPN only to some, can read them as they are.

ADR-12: TOTP secrets are kept with the OATH-LDAP schema of slapd's otp module

Status: Accepted

Context: Users are enrolled for TOTP one-time passwords, and enrolled users must give a code whenever they log in, to OpenVPN and to /auth. Ubuntu's slapd ships the otp module, which holds the OATH-LDAP schema and an overlay that checks a code appended to the password at bind time; both OpenVPN (openvpn-auth-ldap) and /auth check passwords with a bind. Ubuntu packages python3-pyotp. An authenticator app is enrolled from a QR code of an otpauth:// URI.

Decision: The otp module is loaded and its overlay is configured on the package's database, after ppolicy, so every bind of an enrolled user takes the password followed by a current code and slapd records the time step used. The TOTP token is the user entry itself: enrolment adds oathTOTPUser and oathTOTPToken to it, with oathTOTPToken naming the entry, the secret in oathSecret and oathTOTPParams naming one shared parameter entry, cn=totp,ou=policies, with the parameters authenticator apps assume (6 digits, HMAC-SHA1, 30 seconds). An ACL lets the user manager account set oathSecret and no one read it. Enrolment is confirmed: otp_new makes a secret with pyotp and returns it with its URI, storing nothing, and otp_enrol stores the secret it is given back only when a code of it verifies, so a secret is never stored that the user's app does not produce. The router answers the URI; the client renders the QR code.

Consequences: Removing a user removes its token. One check covers OpenVPN and /auth, and an enrolled user types the code after the password in the OpenVPN client. The secret passes through the client between otp_new and otp_enrol, so the router keeps no pending state; enrolling again replaces the secret only once a code of the new one verifies.

ADR-13: Members of admins manage the router; only CLI tokens change admins

Status: Accepted

Context: Signing in through /auth (ADR-3) is open to every user of the directory, most of whom only use OpenVPN. Finer permissions per operation are not needed. Somebody must be able to manage the router before any administrator exists and after every administrator lost access, and administrators must not be able to grant themselves or others the administrator role over the API.

Decision: A token naming a user in sub may call the protected paths only while the user is a member of the group admins, read at each request; other users get 403. vpn-router-token, run as root on the router, makes tokens with the claim admin: true and a lifetime given at creation, without a maximum, signed with the router's key; /auth never issues the claim. An admin token may call everything, and only an admin token may change admins: create it, rename a group to it, change or remove it, add or take out its members, or remove a user who is a member of it. The first member is added with vpn-router-group on the router, which acts as root.

Consequences: Removing a user from admins takes effect at the next request, without waiting for the user's tokens to expire. Membership of admins changes only through root on the router. An admin token is as powerful as root over the API and is revoked only by replacing the key, so it is given a short lifetime unless it is meant for automation.

ADR-14: Failed logins lock the account in slapd; /auth is rate limited per client

Status: Accepted

Context: /auth is open to the internal network and checks passwords, so it invites guessing; OpenVPN checks passwords from the internet. Both check with a bind, so slapd sees every attempt. ppolicy locks an account after a number of failed binds for a fixed time; it has no growing lockout. A Router Manager signs all its users in from one address.

Decision: The default password policy locks an account for 15 minutes after 5 failed binds within 15 minutes; a successful bind clears the count; vpn-router-user unlock and POST /users/<name>/unlock end a lockout and clear the count, and leave a disabled user disabled. /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.

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 service. A manager elsewhere than on the router has its address added to web.trusted_proxies, or its users share one limit.

ADR-15: Refresh tokens are kept in PostgreSQL

Status: Accepted

Context: An access token lives 5 minutes, and a client stays signed in with a refresh token for 8 hours; refresh tokens must be revocable when a user signs out, is disabled, changes the password or is removed, and must survive a restart of the service. The Router Manager keeps its sessions in PostgreSQL too.

Decision: Refresh tokens are random strings, stored as their SHA-256 with the user name and the expiry in the table refresh_tokens, through psycopg 3 (python3-psycopg). The database is web.database, or by default the database and role vpn-router on the router, which vpn-router-setup creates with runuser -u postgres -- psql and a random password in /etc/vpn-router/database.secret, reached over TCP on localhost, as Ubuntu's pg_hba.conf takes peer authentication on the local socket. A refresh token is used once: refreshing deletes it and issues a new one, after checking that the user is neither disabled nor locked.

Consequences: The package depends on postgresql and python3-psycopg. A stolen database holds no usable token. Changing a user's password, disabling, unlocking or removing the user, and signing out, end the user's sessions at once; an access token already issued lives out its 5 minutes.