Support for reconnecting to different host with TcpClient

[rstoyanchev]

Based on an older request (originally reactor/reactor#412), we still have an outstanding request to be able to reconnect to a different host. While the retry operator could be used with the current API, I'm not sure how to combine that with reconnecting to a different host.

For more on the underlying motivation see https://jira.spring.io/browse/SPR-12452.

[smaldini]

Each retry will trigger a new Supplier<InetSocketAddress>#get. It is segregated so any stage downstream can safely retry without dealing with providing a new address. A Load Balancing supplier could be implemented as an extra facility.

[filiphr]

I didn't reply back into the SPR ticket. Honestly, I don't quite get what the older reactor/reactor#412 issue is about. What I did now is to use my own implementation of the Reactor2TcpClient which supports the Supplier<InetSocketAddress>. And I have a round robin supplier (not sure whether that would scale, but I suppose if one is done it will retry the next one). I am talking about the 4.3.x branch. Haven't looked into 5.0. From my understanding of the code I've looked even the 4.3.x branch uses Supplier<InetSocketAddress> and it calls #get on each retry.

From what I could quickly see ReactorNettyTcpClient should be a replacement for the Reactor2TcpClient. With this one it seems it is easier to provide ClientOptions.Builder that would use a Supplier<InetSocketAddress>.

[rstoyanchev]

Ah, I see now. reactor/reactor#412 was about an issue with the Reconnect strategy, passed into the open method, which ignored the IP address. What you're using is the Supplier<InetSocketAddress> on TcpClientSpec. Assuming you've confirmed that works, I'll update SPR-12452 and we can add your suggestion to 4.3.x.

[rstoyanchev]

Resolving this since it sounds like it should just work in the latest Reactor Netty.

[georgeyanev]

@rstoyanchev What is the proper way to configure TcpClient in order to reconnect to the same host in case the server has disconnected? I didn't find methods like open method or Reconnect interface in current reactor-netty code base.

[alexe13]

@georgeyanev I was struggling with reconnect too. Finally I made it work using observe() method, see following gist for example: https://gist.github.com/alexe13/c4afef6be7309447b690cfcd2cc60695
I'm not sure if this is the correct way to handle automatic reconnects, but reactor-netty documentation is pretty scarce so that's better than nothing I guess.

[georgeyanev]

@alexe13 That is interesting, I will try this. After all if there is no response here we have to manage it ourselves.

[violetagg]

@georgeyanev Something similar to the snippet above (provided by @alexe13) can be achieve with

https://github.com/reactor/reactor-netty/blob/master/src/main/java/reactor/netty/Connection.java#L282

See the test cases above.