Caching is both a blessing and a bane for web sites. Cached files and images allow end user to see a previously visited web site almost instantaneously, and those same cached assets can ruin user's experience by serving outdated code that conflicts with recent programming changes. Besides web pages, there are DNS settings that can be cached at multiple locations between web hosting server and end user's computer, pointing web site's domain name to incorrect location. Below is a quick list we compiled that can help you identify specific caching issues and suggested solutions for resolving them Some caching issues, such as caching by broadband provider, can only be identified but do not have immediate actionable solution.
WEB BROWSER CACHE FOR SPECIFIC USER
HOW TO IDENTIFY: Issue is specific to a single computer that was previously used to visit the web site in question, or multiple computers without any underlying similarities, such as a shared network.
SOLUTION: Can be resolved by clearing browser cache and restarting browser. Sometimes, even a simple hard refresh without restarting a browser would suffice.
USER'S DNS CACHE, SERVING OLD PAGE
HOW TO IDENTIFY: Issue is specific to a single computer that was previously used to visit the web site in question, or multiple computers without any underlying similarities, such as a shared network.
SOLUTION: Flush local DNS cache prior to viewing changes or during web site launch.
USER'S HOSTS FILE POINTING TO INCORRECT IP
HOW TO IDENTIFY: Issue is specific to a single computer that had its hosts file edited.
SOLUTION: Can be resolved by quick edit to hosts file.
CACHING ON USER'S LOCAL NETWORK
HOW TO IDENTIFY: Issue will be common to all all computers on specific network.
SOLUTION: Turn off DNS caching or set dnsmasq to 0 names.
CACHING ON USER'S INTERNET CONNECTION PROVIDER
HOW TO IDENTIFY: This will be localized to users in one geographic area served by specific provider. You can also use a service such as https://www.infobyip.com/detectproxy.php to see if your provider uses proxy [server / router].
SOLUTION: Contact internet provider's technical support and request specific web site (domain) to be either excluded from caching (included in do-not-cache list) or have its cached duration reduced to a bare minimum.
HOW TO IDENTIFY: Issue will appear on multiple computers without any underlying similarities, such as a shared network or having previously visited the web site in question.
SOLUTION: Framework cache can be cleared or turned off via CMS. Turning off framework caching is not recommended as it will severely impact web site's performance.
CACHING BY CDN (CONTENT DELIVERY NETWORK)
HOW TO IDENTIFY: Issue will be be either geographically localized to one CDN serving specific region or widespread for multiple regions served by the same CDN provider. Can be identified by accessing web hosting server directly via IP and comparing content with that served via CDN.
SOLUTION: CDN provider's IT needs to force refresh content from web hosting server.
CACHING BY LOAD BALANCER FOR SERVER CLUSTER
HOW TO IDENTIFY: All users accessing site through load balancer will see incorrect cached content, but accessing web server directly by IP will show correct content (might require temporarily disabling load balancer).
SOLUTION: Server admin needs to either force refresh cache or reduce its duration.
SECONDARY SERVER NOT SYNCHRONIZING CONTENT WITH PRIMARY SERVER
HOW TO IDENTIFY: Issue appears for random users during high volume web site traffic, as some users are directed to secondary server with outdated web pages.
SOLUTION: Restart and monitor mirroring process between two servers.
UPSTREAM CACHING BY HOSTING'S BROADBAND PROVIDER
HOW TO IDENTIFY: Depending on the number of upstream providers, the issue can be consistent for all users (in case of a single broadband provider) or random (in case of more than one provider). Can usually be identified by server and network administrator by accessing web site internally from the data center netwrok and getting a different result when accessing the same web site externally.
SOLUTION: Needs to be escalated by hosting provider to broadbank provider's tech support.