To configure Nginx, follow the steps below:

1. Open the Nginx configuration file using the command:

sudo nano /etc/nginx/nginx.conf

2. Add the following line before the line `/etc/nginx/conf.d/*.conf`:

server_names_hash_bucket_size 64;

3. Save the file by pressing `CTRL+X`, then `Y`.

4. Create an Nginx configuration file for Synapse by entering the command:

sudo nano /etc/nginx/conf.d/synapse.conf

5. Copy and paste the following code in the editor. Replace `matrix.example.com` with your server’s domain name:

# enforce HTTPS
server {
    # Client port
    listen 80;
    listen [::]:80;
    server_name matrix.example.com;
    return 301 https://$host$request_uri;
}

server {
    server_name matrix.example.com;

    # Client port
    listen 443 ssl http2;
    listen [::]:443 ssl http2;

    # Federation port
    listen 8448 ssl http2 default_server;
    listen [::]:8448 ssl http2 default_server;

    access_log  /var/log/nginx/synapse.access.log;
    error_log   /var/log/nginx/synapse.error.log;

    # TLS configuration
    ssl_certificate /etc/letsencrypt/live/matrix.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/matrix.example.com/privkey.pem;
    ssl_trusted_certificate /etc/letsencrypt/live/matrix.example.com/chain.pem;
    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_prefer_server_ciphers on;
    ssl_stapling on;
    ssl_stapling_verify on;
    ssl_dhparam /etc/ssl/certs/dhparam.pem;

    location ~ ^(/_matrix|/_synapse/client) {
            proxy_pass http://localhost:8008;
            proxy_http_version 1.1;

            proxy_set_header X-Forwarded-For $remote_addr;
            proxy_set_header X-Forwarded-Proto $scheme;
            proxy_set_header Host $host;

            # Nginx by default only allows file uploads up to 1M in size
            # Increase client_max_body_size to match max_upload_size defined in homeserver.yaml
            client_max_body_size 50M;
    }
}

6. Save the file by pressing `CTRL+X`, then `Y`.

7. Verify the configuration file syntax using the command:

sudo nginx -t

8. Restart Nginx server using the command:

sudo systemctl restart nginx

To install Coturn, follow the steps below:

1. Install Coturn by running the command:

sudo apt install coturn

2. Open the TURN and UDP ports using the commands:

sudo ufw allow 3478
sudo ufw allow 5349
sudo ufw allow :/udp

3. Issue an SSL certificate for Coturn using the command:

sudo certbot certonly --nginx -d coturn.example.com

4. Back up the default configuration file using the command:

sudo mv /etc/turnserver.conf /etc/turnserver.conf.bak

5. Generate an authentication secret and store it in the configuration file using the command:

echo "static-auth-secret=$(cat /dev/urandom | tr -cd '[:alnum:]' | fold -w 256 | head -n 1)" | sudo tee /etc/turnserver.conf

6. Open the Coturn configuration file using the command:

sudo nano /etc/turnserver.conf

7. Paste the following lines below the authentication secret. Replace `coturn.example.com` with your server’s domain name:

use-auth-secret
realm=coturn.example.com
cert=/etc/letsencrypt/live/coturn.example.com/fullchain.pem
pkey=/etc/letsencrypt/live/coturn.example.com/privkey.pem

# VoIP is UDP, no need for TCP
no-tcp-relay

# Do not allow traffic to private IP ranges
no-multicast-peers
denied-peer-ip=0.0.0.0-0.
denied-peer-ip=10.0.0.0-10.
denied-peer-ip=100.64.0.0-
denied-peer-ip=127.0.0.0-127.
denied-peer-ip=169.254.0.0-
denied-peer-ip=172.16.0.0-172.31.255.255
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=192.168.0.0-
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
denied-peer-ip=::1
denied-peer-ip=64:ff9b::-64:ff9b::ffff:ffff
denied-peer-ip=::ffff:0.0.0.0-::ffff:.255
denied-peer-ip=100::-100::ffff:ffff:ffff:ffff
denied-peer-ip=2001::-2001:1ff:ffff:ffff:ffff:ffff:ffff:ffff
denied-peer-ip=2002::-2002:ffff:ffff:ffff:ffff:ffff:ffff:ffff
denied-peer-ip=fc00::-fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
denied-peer-ip=fe80::-febf:ffff:ffff:ffff:ffff:ffff:ffff:ffff

# Limit number of sessions per user
user-quota=12
# Limit total number of sessions
total-quota=1200

8. Save the file by pressing `CTRL+X`, then `Y`. Restart Coturn to apply the settings by running the command:

sudo systemctl restart coturn

To create a Synapse configuration file for Coturn, follow the steps below:

1. Open the Synapse configuration file using the command:

sudo nano /etc/matrix-synapse/conf.d/turn.yaml

2. Paste the following lines in the editor. Replace the `turn_shared_secret` value with the value of the `static-auth-secret` variable from the `/etc/turnserver.conf` file.

turn_uris: [ "turn:coturn.example.com?transport=udp", "turn:coturn.example.com?transport=tcp" ]
turn_shared_secret: 'static-auth-secret'
turn_user_lifetime: 
turn_allow_guests: True

3. Save the file by pressing `CTRL+X`, then `Y`.

4. Restart Synapse to apply the configuration using the command:

sudo systemctl restart matrix-synapse