Back end (or back-end development) is the server-side code and infrastructure that stores data, enforces business rules, handles logins and produces the responses a browser or app requests. Users never see it directly.
Why it matters
Most outages that monitoring tools detect originate in the back end: an application crash, an exhausted database connection pool, a slow query or a failed deploy. Understanding what lives there helps you read symptoms. A 500 error points at application code, while a 502 or 504 often means a gateway could not reach the application behind it.
A typical back end is an application server, a database and often a cache and a job queue.
Example
A request for /orders/42 flows like this:
- The web server forwards it to the application.
- The application checks the session, then queries the database.
- It returns JSON or HTML with status 200, or an error such as 404 if the order does not exist.
Common mistakes
- Assuming a healthy server means a healthy back end. The process can be up while its database is unreachable.
- Doing slow work such as sending email inside the request instead of a background job.
- Trusting data from the browser without validating it again on the server.
Related
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This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.