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previously visited web site almost instantaneously, and those same cached assets can ruin user's experience by serving outdated code that conflicts with recent programming changes.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.
Issues specific to individual user's device
WEB BROWSER CACHE FOR SPECIFIC USER
The most common caching issue is with specific user's web browser cache, which saves web files from previously visisted web pages on local machine for faster viewing of these pages in the future. The drawback of browser cache is that it can retain outdated pages and associated files, such as CSS styles and JavaScript interactive scripts, resulting in unintended user experience.
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.
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
Depending on user's operating system, DNS entries can be stored locally for different periods of time, which might present problems during testing or web site launch.
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.
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
A standard testing approach for a new web site prior to launch is via changes in local hosts file. Hosts file allows creating a custom alias on local machine between development URL (or IP address) and live domain name, so that web site in development can be viewed via browser under its final domain name. Sometimes the local hosts file entry is left even after testing is complete, which would prevent particular user from seeing live site, as the domain name will continue pointing to development site just as it did during testing.
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.
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.
Network-wide issues, to be addressed by network administrator
CACHING ON USER'S LOCAL NETWORK
Network components, such as routers, can store cached DNS information.
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.
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
Caching on internet provider side can occur if the provider uses proxy [server / router] for reducing external traffic.
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: 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.
Web site issues, to be addressed by webmaster
CACHING ON WEB SERVER, DRUPAL, WORDPRESS OR OTHER FRAMEWORK WITH BUILD-IN OR MODULAR CACHING FEATURE
Memory-intensive frameworks such as Drupal can easily overwhelm a web server with just few concurrent web site visitors. To address that, many frameworks come with caching feature that is either part of the core build or available as a module. When turned on, caching makes compiled version of all scripts, pages and styles available for web site visitors without making individual server calls for every code asset used by the framework to generate specific web page.
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.
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.
Hosting-related issues, to be addressed by web server admins and hosting support
CACHING BY CDN (CONTENT DELIVERY NETWORK)
CDNs are used to reduce web server traffic and improve loading times for end user. The issue with CDN might be lack of synchronization with hosting server that has the most recent files and content.
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.
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
Load balancer that directs traffic between multiple web hosting servers can have a caching feature configured and enabled.
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.
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
In a multi-server configuration, primary server mirrors its files to secondary server, which handles excessive web site traffic when primary server begins reaching its limits. If there's an issue with mirroring files between servers, secondary server will be serving different pages than primary server, even if content remains the same (for multi-server configuration, database will usually be handled on a separate 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.
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
Caching of web files and DNS information can also occur at midpoints between user's machine and hosting infrastructure.
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.
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.