astftpd

astftpd is a special purpose read only TFTP server. Unlike other tftp servers it uses IO multiplexing instead of process/thread per a client approach. As a result it can serve 400+ clients concurrently on a very moderate hardware.

Intended usage

Serving a handful of relatively small files to a lot of concurrent clients. For instance booting a cluster of 400+ similar/same machines via the network. Forking/threading TFTP servers are unable to handle such a load so PXE firmware times out, thus rebooting the cluster requires (a complicated) orchestration.

Building and running

make
sudo setcap cap_net_bind_service=+ep ./astftpd
./astftpd /path/to/vmlinuz /path/to/initramfs

Limitations

• astftpd runs only on Linux.
• The list of files being served should be explicitly specified on startup. Linux does not provide IO multiplexing with ordinary files, hence the hack.
• Only IPv4 is supported.
• Multicast TFTP is not implemented (no PXE firmware I know of supports it).
• blksize is the only TFTP option astftpd knowns of.