Possible causes of looong caching times

You have updated some of your website’s image or CSS files but even after hours or days, the Varnish cache still delivers outdated content.

A common cause for this behaviour is a setting in Drupal’s default .htaccess file:

# Cache all files for 2 weeks after access (A).
ExpiresDefault A1209600

You should probably lower this TTL (“Time To Live”) setting to a more reasonable value, for example 4 hours (= 14,400 seconds):

# Cache all files for 4 hours after access A).
ExpiresDefault A14400