I need to create a system comprising of 2 components:
-
A single server that process and stores data. It also periodically sends out updates to the agents
-
Multiple agents that are installed at remote endpoints. These collect data in (often, but not always) long-running operations, and this data needs to get to the server
I’m using C# .NET, and ideally I want to use a standards compliant communications method (i.e. one that could theoritically work with Java too, as we may well also use Java agents in the future). Are there any alternatives to web services? What are my options?
The way I see it I have 3 options using web services, and have made the following observations:
- Client pull
- No open port required at the agent, as it acts like a client
- Would need to poll the server for updates
- Server push
- Open port at the agent, as it acts like a server
- Server must poll agents for results
- Hybrid
- Open port at the agent, as it acts like both a client and a server
- No polling; server pushes out updates when required, client sends results when they are available
The ‘hybrid’ (where agents are both client and server seems the obvious choice – but this application will typically be installed in enterprise and government environments, and I’m concerned they may have an issue with opening a port at the agent. Am I dwelling too much on this?
Are there any other pros and cons I’ve missed out?
Our friends at http://www.infrastructures.org swear by pull-based mechanisms: http://www.infrastructures.org/papers/bootstrap/bootstrap.html
A major reason why they prefer client-pull over server-push is that clients may be down, and clients must (in general) apply all the operations pushed by servers. If this criteria isn’t important in your case, perhaps their conclusion won’t be your conclusion, but I do think it is worth reading the “Push vs Pull” section of their paper to determine for yourself.