Google quietly activated its HTTP Throttling technology in Chrome, which is designed to detect distributed denial of service (DDoS) attacks on websites and dynamically remove the load from sites under attack.

We first noticed HTTP Throttling in Chromium 12 nightly builds back in April and now spotted a developer post, which announced that the throttling trial has ended and the feature is now enabled by default. It was first enabled in build 99173 and is now active in all developer, Canary and nightly builds of Chrome and Chromium.

HTTP throttling will set in when Chrome notices at least 4 server errors from a URL a user has been trying to reach. If the site is not reachable, Chrome automatically assumes that the server may be unavailable or a target of a DDoS attack. Chrome will then deny its user to access the web site for “a short period of time.” The browser will retry to reach the site. If the errors persist, Chrome will increase the “back-off interval” by an “exponential factor” and prevent the browser from accessing the site to reduce the load on it.

Initially, the request intervals will be throttled to 0.7 seconds, but will be scaled to a maximum of 900 seconds (or 15 minutes). According to Google, the perceived downtime will decrease “rapidly” once the maximum back-off kicks in. Users who do not want to run Chrome with HTTP Throttling can disable the feature at chrome://net-internals/#httpThrottling

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