When Not to Embed a Web Server in a Device

Embedding a web server in a product is a potent mechanism for easily implementing various key features and functions in your device. One of the greatest benefits of an embedded web server is that it resides in the equipment itself and not as a separate software that needs to be installed on a computer. A user can use a browser and navigate to the IP address or domain name given to access key features in the product.

In this article, we look into a few use cases where embedding a web server in a product is not optimal, but a hybrid IoT/cloud solution creates a much better user experience.

In general, an embedded web server is not the optimal solution if:

  1. The product is powered by a small microcontroller such as a Cortex M4, and a secure HTTPS server is needed
  2. The product is deployed within a private network (Intranet) but needs to be accessible from the Internet

1: Embedding Web Servers in Microcontrollers

Products powered by small microcontrollers, such as ARM Cortex M4, that mandate using secure HTTPS web servers are problematic since modern web browsers may attempt to pre-allocate as many as 12 connections before sending the first GET request. Each connection requires its own time-consuming TLS handshake.

Too many connections from browser

Figure 1: Modern browsers may request more resources than the device can handle.

HTTPS connections are problematic for small devices. Modern browsers may pre-allocate many TLS connections before sending the first GET request. A small WebServer may be designed to handle one connection at a time, and this works with nonsecure HTTP connections but not with HTTPS connections. It does not work with secure connections because each SSL connection requires its own time-consuming TLS handshake (asymmetric encryption) before it moves up to the HTTP layer. This means that the connections opened by the browser must complete a full TLS handshake, even if they are not used. In particular, some browsers make the handshake very time-consuming since they open many connections (pre-allocate TLS connections) without waiting for at least one to complete the handshake so subsequent connections can use TLS session resumption.

The asymmetric encryption the TLS handshake uses is CPU intensive. A small device can manage one TLS handshake in a reasonable amount of time, but not 12. A device is at the mercy of the browser and has no way of telling the browser that it cannot cope with that many connections. A solution would be to move to HTTP/2, but the HTTP/2 protocol has its issues and complexities making it unsuitable for small devices.

To remedy this problem, two distinct options are suggested:

  • Option 1: Implement a WebSocket Server, which provides more efficient, real-time data transfer compared to traditional web servers.
  • Option 2: Integrate a low-cost ESP32-S3 microcontroller as a co-processor, and utilize the Xedge32 IoT and web development environment for a seamless easy to use non-C programming environment.

2: The product is deployed within an Intranet but needs to be accessible from the Internet

Devices and other products with an embedded web server normally operate on private networks like Intranets. Private networks are not directly accessible via the Internet and are shielded from external Internet access by a firewall/router. For example, even the most basic home router shields any server solution from external Internet access.

Firewall blocks external access

Figure 2: External attacker is unable to access embedded web server on private network

In many cases, preventing external access is beneficial since the embedded web server is protected from potentially malicious external users. However, it creates a major problem if the product with the embedded web server needs to be operated from another network via the Internet. This type of remote access could be anything from remote management and supervision to updating the device firmware.

HTTP Behind Firewall the Hard Way:

External access to one web server on a private network is technically possible by opening a pinhole in the firewall. In computer networking, a firewall pinhole is a port that is not protected by a firewall to allow a particular application to gain access to a service on a host in the network protected by the firewall.

Firewall pinhole

Figure 3: External user accessing private web server via firewall pinhole

How to set up a firewall pinhole depends on the firewall product being used. However, regardless of firewall type, setting up a pinhole such as port forwarding is generally complicated and requires extensive network experience. Unless your customers are very tech-savvy, setting up port forwarding will be near to impossible for them to configure. Customers deploying your products in corporate environments may have IT personnel with the required expertise, but corporate environments typically ban the use of pinholes.

HTTP Behind Firewall the Easy Way:

SharkTrustX is a free product that automates accessing any number of HTTP servers behind firewalls.

IoT & HTTPS Behind Firewall

Figure 4: Accessing an HTTP server behind a firewall using SharkTrustX.

Additional Embedded Web Server Tutorials

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With a wealth of experience creating IoT solutions and embedded device interfaces, we're well-equipped to dramatically improve your products and how you build them. And if you prefer to tackle things on your own, check out our extensive list of embedded web server and IoT tutorials.

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