Understand and use tableflip

Let's discuss the using of tableflip to achieve the Graceful upgrades in Go

Please check the tcp.go to see the demo code of using tableflip. Here we mainly discuss the using of tableflip. About the design of tableflip please see Understand tableflip design

Conclusion about zero downtime upgrade

• short lived socket: opened by client, read/write to the socket, then close it.
  • nc client(see the following demo) is used to test short lived socket.
  • short lived socket has no requirement for zero down time upgrade.
• long lived socket: opened by client, client use it to communicate with server for several round-trip.
  • client/main.go is used to test long lived socket.
  • long lived socket has some requirement for zero down time upgrade:
  • the client should check the network error and reopen the connection if necessary.
  • the server should stop response at application boundary defined by developer.

Demo steps

Run the following command to build the binary.

• go build -o demo tcp.go

Run the following command to start the server.

• ./demo

Run the following command to start the client.

• while true; do nc localhost 8080 -e echo hello; sleep 0.1; done

The server side log is as following.

$ ./demo
[10185] 2021/11/11 23:34:59 listening on  127.0.0.1:8080
[10185] 2021/11/11 23:35:38 receive message from [127.0.0.1:43393]:[hello]
[10185] 2021/11/11 23:35:38 receive message from [127.0.0.1:42929]:[hello]
[10185] 2021/11/11 23:35:38 receive message from [127.0.0.1:33273]:[hello]

Run the following command to restart the server. Note that the [PID] should be replaced with the previous PID.

• kill -s HUP [PID]

Watch the output of server side log. You should notice that the server doesn't report any error during the restart.

[10185] 2021/11/11 23:37:00 receive message from [127.0.0.1:34589]:[hello]
[10185] 2021/11/11 23:37:00 receive message from [127.0.0.1:36367]:[hello]
[10185] 2021/11/11 23:37:00 receive from exitC channel.
[10573] 2021/11/11 23:37:00 listening on  127.0.0.1:8080
[10185] 2021/11/11 23:37:00 quit the listening.
[10185] 2021/11/11 23:37:00 stop listening.
[10185] 2021/11/11 23:37:00 finish the old process.
[10573] 2021/11/11 23:37:00 receive message from [127.0.0.1:37935]:[hello]
[10573] 2021/11/11 23:37:00 receive message from [127.0.0.1:34721]:[hello]
[10573] 2021/11/11 23:37:00 receive message from [127.0.0.1:34245]:[hello]

Run the following command to stop the server. Note that the [PID] should be replaced with the right PID.

• kill -s QUIT [PID]

Watch the output of server side log.

[10573] 2021/11/11 23:39:55 receive message from [127.0.0.1:44181]:[hello]
[10573] 2021/11/11 23:39:55 receive message from [127.0.0.1:37603]:[hello]
[10573] 2021/11/11 23:39:55 receive message from [127.0.0.1:33321]:[hello]
[10573] 2021/11/11 23:39:55 got message SIGQUIT.
[10573] 2021/11/11 23:39:55 receive from exitC channel.
[10573] 2021/11/11 23:39:55 quit the listening.
[10573] 2021/11/11 23:39:56 stop listening.
[10573] 2021/11/11 23:39:56 finish the old process.