communication - PHP: How best to communicate between two servers -

i writing spec complex business solution; set of web apps on own servers. want them independant if 1 has problem or becomes busy rest not affected.

there central server act payment gateway apps providing data apps themselves. data minimal; user ids, have paid app etc.

the idea when app purchased we'd pass data app in question.

the question how while not holding user's experience while wait app server resoned. idea enter queue , process them 1 one on cron job. there concerns not fast enough , user have wait before accessing app.

the other idea app contacts main server when user tries use it. main server can approve user , kept on app server db doesn't have check again.

what think these ideas? there best way of doing it?

the system should able scale 100+ apps , tens of thousands of app purchases hour.

very interested see think! many thanks

i have similar different situation here, supporting potential competitor... have gone mad?? haha

to topic, use curl connect server requests generally, if don't want information public, have specific vps set payment handling, account functions , financial functions, post centralized mysql database access information support single sign on multiple apps on multiple server clusters.

to ensure user moved app want , works correctly, use curl post initial data creating default records in specific app database, set php header redirect using move user app requested single sign-in working part of curl post preformed earlier.

an access key important enables single sign-on secure. generated 1 time per account , never updated though can if there ever security violation. use curl in user auth process ensure user still signed in using key , user id. key never passed publicly posted server side using curl method hiding in php.

i hope helps.