两个隔离系统之间的同步

Question

Need help, some kind of architectural advice... What's the best way of synchronisation between two isolated systems?

One is a standard java environment and the other one is some legacy system without j2ee integration and no scheduling options. The Legacy system has web a service exposed and all processing is started by a call from client (java app). The Processing will be started with approximately 100 web service calls and it will take too long to finish so I can't wait in a thread that long.

I was considering of using an approach where the client starts processing and expose another web service to wait for the legacy system processing. The legacy system would provide information by putting needed data in database (record ID or something like that). That would be another 100 calls, as some kind of answer to init calls. Is this legitimate software architecture solution?

Both systems are reading/writing to same database. Is there any need for 2 webservices because of that? The Legacy system has no option of a scheduled start so I need to initiate it some way.

Answer 1

It's not very clear what you have and what you need. So, let me speculate a little.

1) Legacy system gets 100 requests then process them as a batch all together. New system needs all these 100 answers to continue create new requests. Based on this assumption legacy system doesn't answer with something on each individual request. So, since there is no answer provided then new system should continue to shoot new requests hundred by hundred. However if new system should not make 101 request when 1-st was no done in legacy then synchronization is required. So new one should not wait but not start 101 till it knows 1-st is done. This should be point of the synchronization - not waiting for 101 but check that 1-st is done. It could be done in legacy or new system but that's the point of synchronization.

Answer 2

Your description of the problem and solution fits the http://en.wikipedia.org/wiki/Reactor_pattern . It's a very common approach and well suited.

Answer 3

A few legitimate question: 1) After you reach 100 (or whatever magic number) and you start processing the request batch, what will happen to new requests? refused? queued for the new "100" batch? 2) Soooo. the batch resolution is asynchronous.. you now have two option: Option A: expose a webservice on client that the legacy system will "contact" to "bounce back" the feedback on those 100 elaboration Option B: expose a webservice on legacy server, and the current system will "ping" every 5 minutes, only if there are elaborations awaiting feedback, to tentatively fetch feedback. Personally I'm more of a fan of Option A, but please consider that there are multiple scenario that you need to take in account on both side when dealing with an asynchronous elaboration with queue.. EG say that the legacy system is temporarily unavailable or overloaded, and the new system builds a backlog > of 100 (or whatever the magic number is), you will have to consider as well a mechanism to handle backlog queue giving some kind of "preference"/urgency for queued item.