ADR 0039 — Autocomplete addresses are limited per caller

Status: accepted

Decision

Every autocomplete address limits each caller over a minute and over a day, with four throttles that reuse the API’s own classes under their own scopes: autocomplete_anon_burst, autocomplete_anon_day, autocomplete_user_burst and autocomplete_user_day. A signed-in caller is counted by account and anyone else by network address. A caller over a limit is answered 429 with Retry-After before anything is searched. A portal sets the rates in REST_FRAMEWORK["DEFAULT_THROTTLE_RATES"], and a scope it leaves out uses the default on its throttle class.

The view fixes everything else a request could use to make a search costly: 20 results a page, no page past the 25th, a search cut to 100 characters, and only the filters and ordering the view allows.

Why

The addresses serve public pages, so anyone can call them. The API already limits callers this way and a portal already knows where to set its rates. The search fields get scopes of their own because typing comes in bursts the API’s rates were not set for, and a search box should not use up anyone’s API allowance.

Revisit if

A portal needs limits shared across several servers that the cache it configures cannot give.