How to Enable Fast Open in Nginx on Linux Server

This article will provide a step-by-step guide on enabling Fast Open in Nginx on a Linux server. Fast Open is a TCP feature that allows a client and a server to exchange data during the initial handshake, reducing the latency and improving the overall performance of the connection. Enabling Fast Open makes your Nginx server more efficient and responsive, especially for clients connecting over a high-latency network.

Understanding Fast Open

Fast Open is a TCP feature that enables a client to send data to a server during the initial handshake before the connection is fully established. This is done by including the data in the SYN packet. The first packet is exchanged between the client and the server when establishing a TCP connection.

In traditional TCP connections, the client and server exchange three packets to establish a connection: SYN, SYN-ACK, and ACK. The client sends the SYN packet to the server, the server responds with SYN-ACK, and finally, the client sends ACK to the server, indicating that the connection has been established. This process requires three round trips, which can introduce latency and slow the connection, especially for high-latency networks.

Fast Open addresses this issue by allowing the client to send data in the SYN packet. This way, the client can immediately send data to the server when the connection is established without waiting for the ACK packet. By reducing the number of round trips required to establish a connection, Fast Open can significantly reduce the latency and improve the connection’s performance.

Fast Open is particularly useful for high-latency networks, such as those connecting clients and servers over long distances. By reducing the number of round trips required to establish a connection, Fast Open can make the connection more responsive and improve the user experience for clients connecting over these networks.

Enabling Fast Open in Nginx

Enabling Fast Open in Nginx is a simple process that involves adding a few lines to the server configuration file. Here are the steps to follow:

Step 1: Check if Fast Open is supported

Before enabling Fast Open in Nginx, check if your Linux kernel supports the feature. To do this, you can run the following command:

cat /proc/sys/net/ipv4/tcp_fastopen

If the output is 1, then Fast Open is supported. If the output is 0, then you need to enable it by running the following command:

echo 1 > /proc/sys/net/ipv4/tcp_fastopen

The command presented is a good way to test TCP Fast Open, but the setting may not persist after rebooting your system. To enable TCP Fast Open permanently, use the following command instead:

echo "net.ipv4.tcp_fastopen=3" | sudo tee -a /etc/sysctl.conf

This command utilizes the “echo” command to write the line “net.ipv4.tcp_fastopen=3” to standard output, which is then piped to the “tee” command with the “-a” option. The “tee” command appends the output to the “/etc/sysctl.conf” file and outputs it to standard output. This will make the setting persistent even after rebooting your system, and TCP Fast Open will always be enabled.

Step 2: Add Fast Open to Nginx configuration

Once you have confirmed that Fast Open is supported, you can add the following lines to your Nginx configuration file:

listen 80 fastopen=256;

This line tells Nginx to enable Fast Open for all connections on port 80, with a queue size of 256. The queue size determines how many connections can use Fast Open simultaneously, and you can adjust the queue size to suit your needs. A higher number can potentially improve performance but also require more memory.

To better demonstrate, here are some examples:

Example 1

http {
    tcp_fastopen on;

    server {
        listen 80;
        server_name example.com;

        location / {
            root /var/www/html;
            index index.html;
        }
    }
}

In this example, the fast opening is enabled in the http context, which applies to all server blocks. The server block listens on port 80 for requests to example.com and serves files from /var/www/html.

Example 2

server {
    listen 80 fastopen=10;
    server_name example.com;

    location / {
        root /var/www/html;
        index index.html;
    }
}

In this example, fast open is enabled in the server context using the “fastopen” parameter, which specifies the maximum number of connections to use for fast open. The server block listens on port 80 for requests to example.com and serves files from /var/www/html.

Example 3

location / {
    tcp_fastopen on;
    root /var/www/html;
    index index.html;
}

In this example, fast open is enabled in the location context, which applies only to requests that match this location block. The block serves files from /var/www/html and listens for fast open connections.

Step 3: Restart Nginx

After adding the Fast Open configuration to your Nginx file, you must restart the Nginx service to apply the changes.

First, test the changes with the following command:

sudo nginx -t

If there are no errors, restart the Nginx service using the following command.

sudo service nginx restart

Or

sudo systemctl restart nginx

Testing Fast Open

To test if Fast Open is working on your Nginx server, you can use the following command:

curl --tcp-fastopen http://example.com/

If the server supports this command, send a GET request to the specified URL using Fast Open. If Fast Open is not supported, the command returns to the traditional three-way handshake.

Conclusion

Enabling Fast Open in Nginx on a Linux server can significantly improve the performance and responsiveness of your web applications, especially for clients connecting over high-latency networks. By following the simple steps outlined in this article, you can easily enable Fast Open in Nginx and enjoy the benefits of reduced latency and faster connection times.

Additional Resources and Relevant Links

Here are some additional resources and links related to enabling Fast Open in Nginx on a Linux server:

• Nginx Documentation on Fast Open: The official documentation for Nginx includes a section on how to enable Fast Open. This resource provides a detailed explanation of the Fast Open feature and how to enable it in Nginx.
• Wikipedia Page on TCP Fast Open: This page on Wikipedia provides an overview of TCP Fast Open, including its history, how it works, and the benefits of using it.