echaozh / mother-goose

service graceful reloader in go, may be expanded to a full supervisor

Mother Goose

Mother Goose is used to reload services (configuration and/or binary) gracefully, without abruptly breaking sessions from the clients. It is written in go, and may later expand to a full daemon supervisor.

It is inspired by keter, a Haskell Web app deployment system. It works by listening at an external port by itself, proxying all the traffic from the clients to the backend service listening at a local port. When told to reload the backend service on the receiving of a SIGHUP, it first starts a new instance. When it is reachable via the local port, Mother Goose proxies all the traffic to the new port, and tells the old instance to die off gracefully.

The service should die gracefully on the receiving of a SIGUSR2. By gracefully, we mean the service should close every client connection after finishing the outstanding request on it, and then exit.

An example service is provided, which echos lines from the each client after a 10 second sleep. When you ask Mother Goose to reload the service during that 10 second sleep, you'll see that the first line not echoed will be echoed before the connection to the server breaks off, showing grace.

To try the example, go build in the examples/childe-goose directory, and then cd out to the top and run:

  go run src/mother-goose.go -program examples/childe-goose/childe-goose \
      -external-port 8000 -program-port1 8001 -program-port2 8002

and then telnet to port 8000. Kill the Mother Goose process with SIGHUP to reload Childe Goose.