CODEWITHSUNDEEP
network-programmingwebsocketzeromq
hgoebl
hgoebl

Reputation: 13007

ZeroMQ REQ/REP the other way round

I have a strange szenario:

Webserver / Appserver (Java) sends requests to many different satellite systems (on customers site). Only satellite systems can initiate connection due to firewall rules.

The model I think should be something like REQ/REP, but here the REQuester have to bind and the REPlyer would have to connect.

Is this possible and a stable architecture?

Are there better solutions? (We first had WebSockets in mind...)

Remark: we don't have to use Java on both ends. To be precise on customers site we have Delphi, but we could bridge it somehow.

Upvotes: 3

Views: 196

Answers (1)

raffian
raffian

Reputation: 32086

The model I think should be something like REQ/REP, but here the REQuester have to bind and the REPlyer would have to connect.

This will be problematic. When the server initiates the connection, it must be aware of all peers and their bind address. Not a big deal for a handful of peers, but for many peers changing constantly, it's a mess.

Only satellite systems can initiate connection due to firewall rules.

If that's the case, your mileage will vary with WebSockets; google around, lots of info on this.

Are there better solutions?

Well, with ZeroMq, one solution that comes to mind to support client request initiation is this:

  • Server binds with ROUTER
  • Clients connect with DEALER.

This approach offers bi-directional request/reply, does not block (asynchronous), and eliminates the client-side bind problem mentioned in your question. Here, the server binds, and either side can initiate the conversation.

I recommend reading this section in the guide, it covers extended async request/reply and message enveloping, important when using ROUTER/DEALER sockets.

Upvotes: 2

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