middlingThe difference between a call you wait for and work you hand over — and why one of them is the reason a queue is on almost every diagram in the pool.
queue
worker
service
external api
sync and async
handing work over
redelivery
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1Read the diagram
client_web
Web client
service
Upload API
external_api
Recognition vendor
latency: 3-7 minutes, polling onlyrate limit: 10 requests per second
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People upload a photo, and the upload API calls a recognition vendor that takes three to seven minutes to answer. The call is synchronous — the API waits for it. Two hundred people upload at lunchtime. What happens to the two hundred and first?