Reqflow assumes you've heard most of these words before, but if some of them are fuzzy, this page will get you fluent enough to feel at home everywhere else on the site.
If you can hold these in your head, the diagrams will start to make sense.
The thing making the request, usually a browser or phone app.
A program that listens for requests and sends back responses.
Where data lives long-term. Survives restarts.
Fast temporary storage for things you'll look up again soon. Throws stuff away when full.
A line of pending work, processed in order. Lets a slow worker handle bursts from a fast producer.
A copy of the data on another machine, kept in sync with the primary.
One slice of a dataset that's been split across many machines. Each shard handles its slice independently.
The front door to your system. Every request hits it first, then it routes to the right backend.
Full glossary → when you want more.
A specific route through the site that won't leave you lost.
The smallest real system. You'll feel the whole loop (request → cache → DB → response) in a tiny architecture. Hit play, click every box.
The single most important pattern on the site. Almost every system uses it. Start with the TLDR at the top of the page.
Now apply caching to something bigger. See how 'fan-out on write' uses cache to make every feed-open free.
After those three, you'll know enough that everything else on the site will read like a variation on patterns you've already seen.