Glossary
Every term the courses use, defined in one line and then in a paragraph. Written to be read out of order.
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Doing it twice has the same effect as doing it once.
A property that makes retrying safe. Usually achieved with a key the caller sends on every attempt; the server records processed keys and returns the original result instead of repeating the work. This is what prevents double charges.
See also Retry, At-least-once, Endpoint
The service that vouches for who someone is.
Google, GitHub, Apple, or a dedicated auth service. You delegate the password, the resets, the breach handling and the two-factor to them, and depend on their availability in return.
See also OAuth, Authentication
Reading someone else’s data by changing an id.
Insecure direct object reference: checking that a user is logged in but not that the requested record belongs to them. Trivially exploitable by editing a URL, and extremely common in generated code.
See also Authorization, Authentication
Something is broken for real users right now.
Stop the impact first, understand it second. "What changed recently" answers most incidents, and rolling back is the cheapest action available.
See also Rollback, Postmortem
A lookup structure that makes one kind of query fast.
Like the index at the back of a book. Makes lookups on the indexed column fast, does nothing for other columns, costs storage, and slows down writes. Chosen per query pattern, not sprinkled everywhere.
See also Query, N+1, Full table scan
Rules the data cannot violate.
Constraints enforced by the database itself, such as an order having to belong to a customer that exists. Enforced there, they survive every future bug in every future code path.
See also Foreign key, Transaction
Telling a cache its copy is now wrong.
Actively clearing cached copies when the underlying data changes. Always fresh, but you own the job of finding every place a copy might live. Content-based filenames avoid needing it at all.