In-kernel web server explained

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

Benefits

• Performance: the path taken by data from a source device (i.e. a disk) to a destination device (i.e. a NIC). 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 (NSA is an acronym for Network Server Accelerator)

• Linux

TUX

• Mesibo In-kernel real-time messaging server
• Windows NT

http.sys (part of IIS)

• SPIN

http

• OpenVMS

WASD.trap

See also

• Comparison of web server software
• Service-oriented architecture
• Unikernel/Exokernel (eg. SPIN's loadable kernel modules)

References

• 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