Include additional TURN server example into documentation (#14293)

* Include eturnal TURN server configuration example

and moving specific configuration examples into sub folders.

* Update docs/turn-howto.md

Co-authored-by: Dirk Klimpel <5740567+dklimpel@users.noreply.github.com>

* Update docs/setup/turn/coturn.md

Co-authored-by: Dirk Klimpel <5740567+dklimpel@users.noreply.github.com>

* Update docs/setup/turn/eturnal.md

Co-authored-by: Dirk Klimpel <5740567+dklimpel@users.noreply.github.com>

* Fix TURN relaying public IP address hint

* lint eturnal installation commands

* Adjust synapse setup to link to existing documentation

..avoid redundant information.

* remove redundant text

* include alpine linux package link

* Create 14293.doc

* Update 14293.doc

add missing dot

* Update docs/setup/turn/eturnal.md

Co-authored-by: reivilibre <olivier@librepush.net>

* Update docs/setup/turn/eturnal.md

Co-authored-by: reivilibre <olivier@librepush.net>

* Update docs/setup/turn/coturn.md

Co-authored-by: Moritz Dietz <moritzdietz@users.noreply.github.com>

* Update docs/setup/turn/coturn.md

Co-authored-by: Moritz Dietz <moritzdietz@users.noreply.github.com>

* Update docs/setup/turn/coturn.md

Co-authored-by: Moritz Dietz <moritzdietz@users.noreply.github.com>

* Update docs/setup/turn/eturnal.md

Co-authored-by: reivilibre <olivier@librepush.net>

* Update docs/setup/turn/coturn.md

Co-authored-by: Moritz Dietz <moritzdietz@users.noreply.github.com>

* Update docs/setup/turn/coturn.md

Co-authored-by: Moritz Dietz <moritzdietz@users.noreply.github.com>

* Update eturnal.md to link to official documentation

... and to simplify some aspects

* Adjust coturn to link to default prefix

* Mention eturnalctl location

* Update docs/turn-howto.md

Co-authored-by: Saarko <sandomir@tutanotal.com>
Co-authored-by: Dirk Klimpel <5740567+dklimpel@users.noreply.github.com>
Co-authored-by: reivilibre <olivier@librepush.net>
Co-authored-by: Moritz Dietz <moritzdietz@users.noreply.github.com>

2 files changed, 358 insertions, 0 deletions

diff --git a/docs/setup/turn/coturn.md b/docs/setup/turn/coturn.md
new file mode 100644
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+# coturn TURN server
+
+The following sections describe how to install [coturn](<https://github.com/coturn/coturn>) (which implements the TURN REST API).
+
+## `coturn` setup
+
+### Initial installation
+
+The TURN daemon `coturn` is available from a variety of sources such as native package managers, or installation from source.
+
+#### Debian and Ubuntu based distributions
+
+Just install the debian package:
+
+```sh
+sudo apt install coturn
+```
+
+This will install and start a systemd service called `coturn`.
+
+#### Source installation
+
+1. Download the [latest release](https://github.com/coturn/coturn/releases/latest) from github.  Unpack it and `cd` into the directory.
+
+1.  Configure it:
+
+    ```sh
+    ./configure
+    ```
+
+    You may need to install `libevent2`: if so, you should do so in
+    the way recommended by your operating system. You can ignore
+    warnings about lack of database support: a database is unnecessary
+    for this purpose.
+
+1.  Build and install it:
+
+    ```sh
+    make
+    sudo make install
+    ```
+
+### Configuration
+
+1.  Create or edit the config file in `/etc/turnserver.conf`. The relevant
+    lines, with example values, are:
+
+    ```
+    use-auth-secret
+    static-auth-secret=[your secret key here]
+    realm=turn.myserver.org
+    ```
+
+    See `turnserver.conf` for explanations of the options. One way to generate
+    the `static-auth-secret` is with `pwgen`:
+
+    ```sh
+    pwgen -s 64 1
+    ```
+
+    A `realm` must be specified, but its value is somewhat arbitrary. (It is
+    sent to clients as part of the authentication flow.) It is conventional to
+    set it to be your server name.
+
+1.  You will most likely want to configure `coturn` to write logs somewhere. The
+    easiest way is normally to send them to the syslog:
+
+    ```sh
+    syslog
+    ```
+
+    (in which case, the logs will be available via `journalctl -u coturn` on a
+    systemd system). Alternatively, `coturn` can be configured to write to a
+    logfile - check the example config file supplied with `coturn`.
+
+1.  Consider your security settings. TURN lets users request a relay which will
+    connect to arbitrary IP addresses and ports. The following configuration is
+    suggested as a minimum starting point:
+
+    ```
+    # VoIP traffic is all UDP. There is no reason to let users connect to arbitrary TCP endpoints via the relay.
+    no-tcp-relay
+
+    # 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
+    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
+    ```
+
+1.  Also consider supporting TLS/DTLS. To do this, add the following settings
+    to `turnserver.conf`:
+
+    ```
+    # TLS certificates, including intermediate certs.
+    # For Let's Encrypt certificates, use `fullchain.pem` here.
+    cert=/path/to/fullchain.pem
+
+    # TLS private key file
+    pkey=/path/to/privkey.pem
+
+    # Ensure the configuration lines that disable TLS/DTLS are commented-out or removed
+    #no-tls
+    #no-dtls
+    ```
+
+    In this case, replace the `turn:` schemes in the `turn_uris` settings below
+    with `turns:`.
+
+    We recommend that you only try to set up TLS/DTLS once you have set up a
+    basic installation and got it working.
+
+    NB: If your TLS certificate was provided by Let's Encrypt, TLS/DTLS will
+    not work with any Matrix client that uses Chromium's WebRTC library. This
+    currently includes Element Android & iOS; for more details, see their
+    [respective](https://github.com/vector-im/element-android/issues/1533)
+    [issues](https://github.com/vector-im/element-ios/issues/2712) as well as the underlying
+    [WebRTC issue](https://bugs.chromium.org/p/webrtc/issues/detail?id=11710).
+    Consider using a ZeroSSL certificate for your TURN server as a working alternative.
+
+1.  Ensure your firewall allows traffic into the TURN server on the ports
+    you've configured it to listen on (By default: 3478 and 5349 for TURN
+    traffic (remember to allow both TCP and UDP traffic), and ports 49152-65535
+    for the UDP relay.)
+
+1.  If your TURN server is behind NAT, the NAT gateway must have an external,
+    publicly-reachable IP address. You must configure `coturn` to advertise that
+    address to connecting clients:
+
+    ```
+    external-ip=EXTERNAL_NAT_IPv4_ADDRESS
+    ```
+
+    You may optionally limit the TURN server to listen only on the local
+    address that is mapped by NAT to the external address:
+
+    ```
+    listening-ip=INTERNAL_TURNSERVER_IPv4_ADDRESS
+    ```
+
+    If your NAT gateway is reachable over both IPv4 and IPv6, you may
+    configure `coturn` to advertise each available address:
+
+    ```
+    external-ip=EXTERNAL_NAT_IPv4_ADDRESS
+    external-ip=EXTERNAL_NAT_IPv6_ADDRESS
+    ```
+
+    When advertising an external IPv6 address, ensure that the firewall and
+    network settings of the system running your TURN server are configured to
+    accept IPv6 traffic, and that the TURN server is listening on the local
+    IPv6 address that is mapped by NAT to the external IPv6 address.
+
+1.  (Re)start the turn server:
+
+    * If you used the Debian package (or have set up a systemd unit yourself):
+      ```sh
+      sudo systemctl restart coturn
+      ```
+
+    * If you built from source:
+
+      ```sh
+      /usr/local/bin/turnserver -o
+      ```
diff --git a/docs/setup/turn/eturnal.md b/docs/setup/turn/eturnal.md
new file mode 100644
index 0000000000..2e5a45673e
--- /dev/null
+++ b/docs/setup/turn/eturnal.md
@@ -0,0 +1,170 @@
+# eturnal TURN server
+
+The following sections describe how to install [eturnal](<https://github.com/processone/eturnal>) 
+(which implements the TURN REST API).
+
+## `eturnal` setup
+
+### Initial installation
+
+The `eturnal` TURN server implementation is available from a variety of sources 
+such as native package managers, binary packages, installation from source or 
+[container image](https://eturnal.net/documentation/code/docker.html). They are 
+all described [here](https://github.com/processone/eturnal#installation).
+
+Quick-Test instructions in a [Linux Shell](https://github.com/processone/eturnal/blob/master/QUICK-TEST.md) 
+or with [Docker](https://github.com/processone/eturnal/blob/master/docker-k8s/QUICK-TEST.md) 
+are available as well.
+
+### Configuration
+
+After installation, `eturnal` usually ships a [default configuration file](https://github.com/processone/eturnal/blob/master/config/eturnal.yml) 
+here: `/etc/eturnal.yml` (and, if not found there, there is a backup file here: 
+`/opt/eturnal/etc/eturnal.yml`). It uses the (indentation-sensitive!) [YAML](https://en.wikipedia.org/wiki/YAML) 
+format. The file contains further explanations.
+
+Here are some hints how to configure eturnal on your [host machine](https://github.com/processone/eturnal#configuration) 
+or when using e.g. [Docker](https://eturnal.net/documentation/code/docker.html).
+You may also further deep dive into the [reference documentation](https://eturnal.net/documentation/).
+
+`eturnal` runs out of the box with the default configuration. To enable TURN and 
+to integrate it with your homeserver, some aspects in `eturnal`'s default configuration file 
+must be edited:
+
+1.  Homeserver's [`turn_shared_secret`](../../usage/configuration/config_documentation.md#turn_shared_secret) 
+    and eturnal's shared `secret` for authentication
+
+    Both need to have the same value. Uncomment and adjust this line in `eturnal`'s 
+    configuration file:
+
+    ```yaml
+    secret: "long-and-cryptic"     # Shared secret, CHANGE THIS.
+    ```
+
+    One way to generate a `secret` is with `pwgen`:
+
+    ```sh
+    pwgen -s 64 1
+    ```
+
+1.  Public IP address
+
+    If your TURN server is behind NAT, the NAT gateway must have an external,
+    publicly-reachable IP address. `eturnal` tries to autodetect the public IP address, 
+    however, it may also be configured by uncommenting and adjusting this line, so 
+    `eturnal` advertises that address to connecting clients:
+
+    ```yaml
+    relay_ipv4_addr: "203.0.113.4" # The server's public IPv4 address.
+    ```
+
+    If your NAT gateway is reachable over both IPv4 and IPv6, you may
+    configure `eturnal` to advertise each available address:
+
+    ```yaml
+    relay_ipv4_addr: "203.0.113.4" # The server's public IPv4 address.
+    relay_ipv6_addr: "2001:db8::4" # The server's public IPv6 address (optional).
+    ```
+
+    When advertising an external IPv6 address, ensure that the firewall and
+    network settings of the system running your TURN server are configured to
+    accept IPv6 traffic, and that the TURN server is listening on the local
+    IPv6 address that is mapped by NAT to the external IPv6 address.
+
+1.  Logging
+
+    If `eturnal` was started by systemd, log files are written into the
+    `/var/log/eturnal` directory by default. In order to log to the [journal](https://www.freedesktop.org/software/systemd/man/systemd-journald.service.html)
+    instead, the `log_dir` option can be set to `stdout` in the configuration file.
+
+1.  Security considerations
+
+    Consider your security settings. TURN lets users request a relay which will
+    connect to arbitrary IP addresses and ports. The following configuration is
+    suggested as a minimum starting point, [see also the official documentation](https://eturnal.net/documentation/#blacklist):
+
+    ```yaml
+    ## Reject TURN relaying from/to the following addresses/networks:
+    blacklist:                 # This is the default blacklist.
+        - "127.0.0.0/8"        # IPv4 loopback.
+        - "::1"                # IPv6 loopback.
+        - recommended          # Expands to a number of networks recommended to be
+                               # blocked, but includes private networks. Those
+                               # would have to be 'whitelist'ed if eturnal serves
+                               # local clients/peers within such networks.
+    ```
+
+    To whitelist IP addresses or specific (private) networks, you need to **add** a 
+    whitelist part into the configuration file, e.g.:
+
+    ```yaml
+    whitelist:
+        - "192.168.0.0/16"
+        - "203.0.113.113"
+        - "2001:db8::/64"
+    ```
+
+    The more specific, the better.
+
+1.  TURNS (TURN via TLS/DTLS)
+
+    Also consider supporting TLS/DTLS. To do this, adjust the following settings
+    in the `eturnal.yml` configuration file (TLS parts should not be commented anymore):
+
+    ```yaml
+    listen:
+        - ip: "::"
+          port: 3478
+          transport: udp
+        - ip: "::"
+          port: 3478
+          transport: tcp
+        - ip: "::"
+          port: 5349
+          transport: tls
+
+    ## TLS certificate/key files (must be readable by 'eturnal' user!):
+    tls_crt_file: /etc/eturnal/tls/crt.pem
+    tls_key_file: /etc/eturnal/tls/key.pem
+    ```
+
+    In this case, replace the `turn:` schemes in homeserver's `turn_uris` settings
+    with `turns:`. More is described [here](../../usage/configuration/config_documentation.md#turn_uris).
+
+    We recommend that you only try to set up TLS/DTLS once you have set up a
+    basic installation and got it working.
+
+    NB: If your TLS certificate was provided by Let's Encrypt, TLS/DTLS will
+    not work with any Matrix client that uses Chromium's WebRTC library. This
+    currently includes Element Android & iOS; for more details, see their
+    [respective](https://github.com/vector-im/element-android/issues/1533)
+    [issues](https://github.com/vector-im/element-ios/issues/2712) as well as the underlying
+    [WebRTC issue](https://bugs.chromium.org/p/webrtc/issues/detail?id=11710).
+    Consider using a ZeroSSL certificate for your TURN server as a working alternative.
+
+1.  Firewall
+
+    Ensure your firewall allows traffic into the TURN server on the ports
+    you've configured it to listen on (By default: 3478 and 5349 for TURN
+    traffic (remember to allow both TCP and UDP traffic), and ports 49152-65535
+    for the UDP relay.)
+
+1.  Reload/ restarting `eturnal`
+
+    Changes in the configuration file require `eturnal` to reload/ restart, this
+    can be achieved by:
+
+    ```sh
+    eturnalctl reload
+    ```
+    
+    `eturnal` performs a configuration check before actually reloading/ restarting
+    and provides hints, if something is not correctly configured.
+
+### eturnalctl opterations script
+
+`eturnal` offers a handy [operations script](https://eturnal.net/documentation/#Operation) 
+which can be called e.g. to check, whether the service is up, to restart the service, 
+to query how many active sessions exist, to change logging behaviour and so on.
+
+Hint: If `eturnalctl` is not part of your `$PATH`, consider either sym-linking it (e.g. ´ln -s /opt/eturnal/bin/eturnalctl /usr/local/bin/eturnalctl´) or call it from the default `eturnal` directory directly: e.g. `/opt/eturnal/bin/eturnalctl info`