Is it possible to auto-update a chrome extension published on the chrome web store?
When you publish to Chrome Web Store (CWS), CWS hosts your extension and you loose control over update_url attribute in manifest.json (it's overriten by CWS specific link). When you decide to make new version of your CWS-hosted extension available, you simply upload it (with higher version number) to CWS (via developer dashboard). After that, you just wait for Chrome auto-update feature to do all the work.
Each Chrome performs, in the background and without users direct permission, a routine checks in CWS (or somewhere else if extension is self-hosted) making sure that all extensions are up to date. If new version of any extension (or app) is available, Chrome performs an auto-update (if extension's permissions haven't increased).
There is now a way to update extensions hosted in CWS programmatically (since March 2014) by using Webstore API.
After registering for the API and authorizing through OAuth 2.0, you can push an update for an existing item:
curl \-H "Authorization: Bearer $TOKEN" \-H "x-goog-api-version: 2" \-X PUT \-T $FILE_NAME \-v \https://www.googleapis.com/upload/chromewebstore/v1.1/items/$APP_IDDocumentation is not clear whether this creates a draft or not; in any case, publishing is also possible through the API.
Please note that it will still be subject to automatic review checks, so the actual update will only be available after they complete (usually under an hour).