Socket Takeover: Socket takeover from one process to another

When you are running business mission critical services you MUST rely on design offering zero downtime. It is truly the case when considering upgrading/updating such mission critical software components.

This software introduce a design pattern to perform seamless TCP socket takeover from one process to another. The code here is just a proof of concept and can be used for experimentation or integration into more complex software component.

This source code is using design present in 4.4BSD systems. Using SCM_RIGHTS ancillary data over a Unix domain socket to transport a set of file descriptors. You can find more informations on this technic by reading good litterature from [W. Richard Stevens: UNIX Network Programming Volume 1 Third Edition], section 15.7. The code proposed here will make it more Linux specific by introducting a mechanism to takeover and synchronize client/server interactions.

Content

2 directories are available :

* server : TCP server code
* client : TCP client code

Give it a try : Server side

$ cd server
$ make
$ ./server -h
Usage: ./server [OPTION...]
  -a, --listen-address		Address to bind TCP listener on
  -p, --listen-port		Port to bind TCP listener on
  -b, --listen-backlog		TCP listener backlog
  -t, --takeover-path		Takeover channel unix domain path
  -T, --takeover		Perform takeover operation
  -h, --help			Display this help message
$ ./server -a 127.0.0.1 -p 1234 -t /tmp/.takeover

Give it a try : Client side

$ cd client
$ make
$ ./client -h
Usage: ./client [OPTION...]
  -a, --connect-address		Connection Address
  -p, --connect-port		Connection Port
  -h, --help			Display this help message
$ ./client -a 127.0.0.1 -p 1234

Having fun

[client]$ ./client -a 127.0.0.1 -p 1234


[server/sh1]$ ./server -a 127.0.0.1 -p 1234 -t /tmp/.takeover
Starting TCP server on [127.0.0.1]:1234 (fd:3)
Starting Takeover channel on [/tmp/.takeover] domain socket
Accepting connection from Peer [127.0.0.1]:57796 (fd:4)
Starting connection with Peer [127.0.0.1]:57796 (fd:4)
[127.0.0.1]:57796 - seqnum:0
[127.0.0.1]:57796 - seqnum:1
[127.0.0.1]:57796 - seqnum:2
[127.0.0.1]:57796 - seqnum:3
[127.0.0.1]:57796 - seqnum:4
[127.0.0.1]:57796 - seqnum:5
[127.0.0.1]:57796 - seqnum:6
[127.0.0.1]:57796 - seqnum:7
[127.0.0.1]:57796 - seqnum:8
[127.0.0.1]:57796 - seqnum:9
[127.0.0.1]:57796 - seqnum:10
[127.0.0.1]:57796 - seqnum:11
[127.0.0.1]:57796 - seqnum:12
[127.0.0.1]:57796 - seqnum:13
[127.0.0.1]:57796 - seqnum:14
[127.0.0.1]:57796 - seqnum:15
[127.0.0.1]:57796 - seqnum:16
[127.0.0.1]:57796 - seqnum:17
[127.0.0.1]:57796 - seqnum:18
[127.0.0.1]:57796 - seqnum:19
Accepting connection from Takeover channel
Current fd_array:={[3][4]}
[127.0.0.1]:57796 - seqnum:20
Holding connection with Peer [127.0.0.1]:57796 (fd:4)
Releasing Peer [127.0.0.1]:57796 (fd:4)
tcp_peer_release(): Tcp peers released...


[server/sh2]$ ./server -T /tmp/.takeover 
Starting connection with Peer [127.0.0.1]:57796 (fd:5)
Starting Takeover channel on [/tmp/.takeover] domain socket
[127.0.0.1]:57796 - seqnum:21
[127.0.0.1]:57796 - seqnum:22
[127.0.0.1]:57796 - seqnum:23
[127.0.0.1]:57796 - seqnum:24
[127.0.0.1]:57796 - seqnum:25
[127.0.0.1]:57796 - seqnum:26
[127.0.0.1]:57796 - seqnum:27
[127.0.0.1]:57796 - seqnum:28
[127.0.0.1]:57796 - seqnum:29
...

Enjoy, Alexandre