08Website know-how & errors

Understanding caching – clear browser, Redis, DNS and Cloudflare

Why you still see the old page after a change at Nexthosting – which caches exist (browser, page cache, Redis, DNS, Cloudflare) and how to clear each one.

In short

A cache is a temporary store that remembers answers so everything goes faster. The catch: after a change, the old version may still be sitting somewhere. Between the server and your screen there can be up to five caches. Clear them from the inside out: WordPress and server, then CDN, then DNS and finally the browser.

Why caches exist

Building a page takes work: PHP runs, the database is queried, images are loaded. Delivering a finished copy saves time and computing power. That is why there are several temporary stores one after another.

The path of a page – and where it is remembered along the way

Browser cacheYour device remembers files
DNS cacheAddress of the domain remembered
CDN or proxye.g. Cloudflare
Page cache on the serverFinished HTML
Object cache (Redis)Database results
PHP and databaseThe "real" page

The caches at a glance

Cache	Where?	What is remembered?	Typical problem
Browser	Your device	Images, CSS, scripts, whole pages	Old version after a change
DNS	Computer, router, resolver	Address of a domain (TTL)	Old page after a move
CDN/proxy (e.g. Cloudflare)	Third-party servers	Files, possibly pages	Old files, 52x errors
Page cache	Server or plugin	Finished HTML pages	Changes appear with a delay
Object cache (Redis)	Server	Database queries	Old settings or menus
OPcache	Server (PHP)	Compiled PHP code	A changed PHP file does not take effect immediately

You see an old version – who else still sees it?

Only meBrowser or DNS cache on your device

Others too, after a change to the websitePage or object cache, possibly CDN

Others too, after a move or DNS changeDNS, wait for the TTL

52x error displayedCloudflare

Clear the browser cache

A quick test without deleting anything: a private window (Ctrl+Shift+N or Ctrl+Shift+P) or another browser.

Windows and Linux: Ctrl+F5 or Ctrl+Shift+R
macOS: Cmd+Shift+R

This reloads the page without stored files.

With the browser cache, the server decides with headers how long it applies (Cache-Control, Expires). An example of how to set this up is in .htaccess basics. The status code 304 Not Modified means: the browser asked whether anything had changed and used its stored copy (HTTP status codes).

Page cache and object cache

Page cache (WordPress and others)

A cache plugin or a server feature stores finished pages. After a change the cache has to be cleared; often this happens automatically on saving. Otherwise:

In WordPress, open the menu of your cache plugin.
Click Clear cache (depending on the plugin “Purge All” or similar).
Also clear the minify/CSS cache if styles do not appear.
Reload the page in a private window.

Use one cache plugin, not several at once.

Object cache (Redis)

The object cache remembers the results of database queries. Nexthosting WordPress hosting includes Redis in every plan; with web hosting it is available from the Pro plan. It speeds up dynamic pages but can deliver old values, such as menus or settings.

Clear it through the Redis plugin in WordPress (“Flush Cache” button).
Via SSH with WP-CLI:

wp cache flush

OPcache

PHP stores compiled code. The server usually detects new files by itself after a short time. If a changed PHP file stubbornly has no effect, a PHP restart in the web panel (if offered) or a note to support helps.

DNS cache and TTL

DNS answers are remembered for as long as the TTL allows. After a move, some visitors therefore still see the old page.

DNS change and cache

Before the changeLower the TTLe.g. to 300 seconds
ChangeSet the new record
Until the TTLMixed phaseOld and new answers
AfterwardsEveryone sees the new pageRaise the TTL again

Clear the local DNS cache:

ipconfig /flushdns

sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

sudo resolvectl flush-caches

More in DNS basics and Solving DNS problems.

Cloudflare

If your domain uses Cloudflare as an intermediary, there is another cache there.

Log in to Cloudflare and choose your domain.
Open Caching, then Configuration.
Choose Purge Everything or purge individual addresses (Custom Purge).
During development you can switch on Development Mode: the cache is bypassed for three hours.

Also check the SSL mode (recommended: “Full” or “Full (strict)”), otherwise redirect loops threaten. Errors 520 to 526 come from Cloudflare (HTTP status codes).

Check the cache

With curl you can see headers that point to a cache:

curl -sI https://meinprojekt.de/ | grep -iE "cache|age|etag|last-modified|cf-cache-status"

Header	Meaning
`cache-control`	How long may it be stored?
`age`	For how many seconds has the response been in the cache?
`etag`, `last-modified`	Version markers so the browser can check back
`cf-cache-status: HIT`	Cloudflare delivered from its cache (`MISS` = fetched fresh)

Order of clearing

Clear the WordPress cache plugin and the object cache.
If present: clear Cloudflare or another CDN.
Clear the browser cache or use a private window.
For moves: clear the DNS cache and wait out the TTL.

Frequently asked questions

Should I always switch the cache off?

No. Without a cache the site gets slower. Only switch it off for testing or clear it selectively.

Why do I see changes in the admin area but not on the site?

Usually the page cache or the CDN sits in between. Clear both.

Does this apply to game servers too?

Game servers do not use web caches. With server pages and banners, however, the browser can show old images.