Advice on disconnected messages with WCF through firewalls

All,

I'm looking for advice over the following scenario:

I have a component running in one part of the corporate network that sends messages开发者_运维问答 to an application logic component for processing. These components might reside on the same server, different servers in the same network (LAN ot WAN) or live outside in the cloud. The application server should be scalable and resilient.

The messages are related in that the sequence they arrive is important. They are time-stamped with the client timestamp.

My thinking is that I'll get the clients to use WCF basicHttpBinding (some are based on .NET CF which only has basic) to send messages to the Application Server (this is because we can guarantee port 80/443 will be open for outgoing connections). Server accepts these, and writes these into a queue. This queue can be scaled out if needed over multiple machines.

I'm hesitant to use MSMQ for the queue though as to properly scale out we are going to have to install seperate private queues on each application server and round-robin monitor the queues. I'm concerned though that we could lose a message on a server that's gone down until the server is restored, and we could end up processing a later message from a different server and disrupt the sequence.

What I'd prefer is a central queue (e.g. a database table) that all application servers monitor.

With this in mind, what I'd like to do is to create a custom WCF binding, similar to netMsmqBinding, but that uses the DB table instead but I'm confused as to whether I can simply create a custom transport or a I need a full binding, and whether the binding will allow the client to send over HTTP. I've looked around the internet but I'm a little confused as to where to start.

I could not bother with the custom WCF binding but it seems a good way to introduce scalability if I do need to seperate the servers.

Any suggestions please would be helpful, including alternatives. Many thanks

I would start with MSMQ because it is exactly for this purpouse. Use single transactional queue on clustered machine and let application servers to take messages for processing from this queue. Each message processing has to be part of distributed transaction (MSDTC).

This scenario will ensure:

• clustered queue host will ensure that if one cluster node fails the other will still be able to handle requests

• sending each message as recoverable - it means that message will be persisted on hard drive (not only in memory) so in critical failure of the whole cluster you will still have all messages.

• transactional queue will ensure that all message transport operations will be atomic - moving message from outgoing queue to destination queue will be processed as transaction. It means that original message from outgoing queue will be kept in queue until ack from destination queue arrives. Transactional processing can ensure in order delivery.

• Distributed transaction will allow application servers consuming messages in transaction. Message will not be deleted from queue until application server commits transaction or transaction time outs.

• MSMQ is also available on .NET CF so you can send messages directly to queue without intermediate non-reliable web service layer.

• It should be possible to configure MSMQ over HTTP (but I have never used it so I'm not sure how it cooperates with previous mentioned features).

Your proposed solution will be pretty hard. You will end up in building BizTalk's MessageBox. But if you really want to do it, check Omar's post about building database queue table.