app/matrix/lib/coturn.libsonnet

local kube = import "../../../kube/kube.libsonnet";

{
    local app = self,
    local cfg = app.cfg,
    cfg:: {
        image: error "cfg.image must be set",
        realm: error "cfg.realm must be set",
        authSecret: error "cfg.authSecret must be set",
        storageClassName: error "cfg.storageClassName must be set",

        portStart: 49152,
        portEnd: 49172,
        loadBalancerIP: null,
    },

    ns:: error "ns needs to be provided",

    configMap: app.ns.Contain(kube.ConfigMap("coturn")) {
        data: {
            "coturn.conf": |||
                # VoIP traffic is all UDP. There is no reason to let users connect to arbitrary TCP endpoints via the relay.
                no-tcp-relay

                no-tls
                no-dtls

                # don't let the relay ever try to connect to private IP address ranges within your network (if any)
                # given the turn server is likely behind your firewall, remember to include any privileged public IPs too.
                denied-peer-ip=10.0.0.0-10.255.255.255
                denied-peer-ip=192.168.0.0-192.168.255.255
                denied-peer-ip=172.16.0.0-172.31.255.255

                # recommended additional local peers to block, to mitigate external access to internal services.
                # https://www.rtcsec.com/article/slack-webrtc-turn-compromise-and-bug-bounty/#how-to-fix-an-open-turn-relay-to-address-this-vulnerability
                no-multicast-peers
                denied-peer-ip=0.0.0.0-0.255.255.255
                denied-peer-ip=100.64.0.0-100.127.255.255
                denied-peer-ip=127.0.0.0-127.255.255.255
                denied-peer-ip=169.254.0.0-169.254.255.255
                denied-peer-ip=192.0.0.0-192.0.0.255
                denied-peer-ip=192.0.2.0-192.0.2.255
                denied-peer-ip=192.88.99.0-192.88.99.255
                denied-peer-ip=198.18.0.0-198.19.255.255
                denied-peer-ip=198.51.100.0-198.51.100.255
                denied-peer-ip=203.0.113.0-203.0.113.255
                denied-peer-ip=240.0.0.0-255.255.255.255

                # special case the turn server itself so that client->TURN->TURN->client flows work
                # this should be one of the turn server's listening IPs
                # FIXME allowed-peer-ip=10.0.0.1

                # consider whether you want to limit the quota of relayed streams per user (or total) to avoid risk of DoS.
                user-quota=12 # 4 streams per video call, so 12 streams = 3 simultaneous relayed calls per user.
                total-quota=1200

                use-auth-secret
            |||,
        },
    },

    dataVolume: app.ns.Contain(kube.PersistentVolumeClaim("coturn-data")) {
        spec+: {
            storageClassName: cfg.storageClassName,
            resources: {
                requests: {
                    storage: "10Gi",
                },
            },
        },
    },

    deployment: app.ns.Contain(kube.Deployment("coturn")) {
        spec+: {
            replicas: 1,
            template+: {
                spec+: {
                    volumes_: {
                        config: kube.ConfigMapVolume(app.configMap),
                        data: kube.PersistentVolumeClaimVolume(app.dataVolume),
                    },
                    containers_: {
                        coturn: kube.Container("coturn") {
                            image: cfg.image,
                            ports_: {
                                turn: { containerPort: 3478 },
                            } + {
                                ["fwd-%d" % [n]]: { containerPort: n }
                                for n in std.range(cfg.portStart, cfg.portEnd)
                            },

                            command: [
                                # This disgusting hack comes from the fact that
                                # official coturn containers have turnserver
                                # binary set up with CAP_NET_BIND_SERVICE=+ep,
                                # while there's really no use that in our case.
                                #
                                # Due to our PSP we can't exec said binary, nor
                                # can we chmod/chown/setcap on it, as we are
                                # running as an unprivileged user.
                                #
                                # Copying it over is the easiest method of
                                # stripping said spurious cap.
                                "/bin/sh", "-c",
                                "cp /usr/bin/turnserver /tmp/turnserver && \\
                                exec /tmp/turnserver \\
                                    -c /config/coturn.conf \\
                                    --log-binding \\
                                    --realm=$(COTURN_REALM) \\
                                    --static-auth-secret=$(COTRN_STATIC_AUTH_SECRET) \\
                                    --min-port $(COTURN_MIN_PORT) \\
                                    --max-port $(COTURN_MAX_PORT) \\
                                    " + if cfg.loadBalancerIP != null then "-X $(COTURN_EXTERNAL_IP)" else "",
                            ],
                            volumeMounts_: {
                                config: { mountPath: "/config" },
                                data: { mountPath: "/var/lib/coturn" },
                            },
                            env_: {
                                COTURN_REALM: cfg.realm,
                                COTURN_STATIC_AUTH_SECRET: cfg.authSecret,
                                COTURN_EXTERNAL_IP: cfg.loadBalancerIP,
                                COTURN_MIN_PORT: cfg.portStart,
                                COTURN_MAX_PORT: cfg.portEnd,
                            },
                        },
                    },
                    securityContext: {
                        runAsUser: 1000,
                        runAsGroup: 1000,
                        fsGroup: 2000,
                    },
                },
            },
        },
    },

    svcTCP: app.ns.Contain(kube.Service("coturn-tcp")) {
        target_pod:: app.deployment.spec.template,
        metadata+: {
            annotations+: {
                "metallb.universe.tf/allow-shared-ip": "coturn",
            },
        },
        spec+: {
            type: "LoadBalancer",
            loadBalancerIP: cfg.loadBalancerIP,
            externalTrafficPolicy: "Local",
            ports: [
                { name: "turn", port: 3478, protocol: "TCP" },
            ] + [
                { name: "fwd-%d" % [n], port: n, protocol: "TCP" }
                for n in std.range(cfg.portStart, cfg.portEnd)
            ],
        },
    },

    svcUDP: app.ns.Contain(kube.Service("coturn-udp")) {
        target_pod:: app.deployment.spec.template,
        metadata+: {
            annotations+: {
                "metallb.universe.tf/allow-shared-ip": "coturn",
            },
        },
        spec+: {
            type: "LoadBalancer",
            loadBalancerIP: cfg.loadBalancerIP,
            externalTrafficPolicy: "Local",
            ports: [
                { name: "turn", port: 3478, protocol: "UDP" },
            ] + [
                { name: "fwd-%d" % [n], port: n, protocol: "UDP" }
                for n in std.range(cfg.portStart, cfg.portEnd)
            ],
        },
    },
}