In-kernel web server

An in-kernel web server is an unlimited HTTP server that runs in kernel space or equivalent. It is also called "accelerator".

Benefits

• Performance. The path taken by data from disk to network. Proper asynchronous zero-copy interfaces would make this available from user-space.
• Scalability with respect to number of simultaneous clients. Event notification of comparable scalability seems unlikely in user-space.

Drawbacks

• Security: Kernel processes run with unlimited privileges.
• Portability. Every kernel needs a specific implementation route.
• Reliability. Failure in the webserver may crash the OS.

Implementations

• illumos/Solaris: NCAkmod aka Network Cache and Accelerator (NCA) kernel module
• HP-UX: NSAhttp
• Linux: TUX
• Windows NT: http.sys (part of IIS)
• SPIN: http
• OpenVMS: WASD.trap

See also

• Comparison of lightweight web servers
• Comparison of web server software

References

• ^1 CITI_TR_00-4
• High-Performance Memory-Based Web Servers: Kernel and User-Space Performance. Philippe Joubert, Robert B. King, Rich Neves, Mark Russinovich, John M. Tracey. IBM. T. J. Watson Research Center