{"id":11115,"date":"2026-10-01T13:56:14","date_gmt":"2026-10-01T13:56:14","guid":{"rendered":"https:\/\/schindlerengineering.com\/public\/?p=11115"},"modified":"2026-10-01T13:56:14","modified_gmt":"2026-10-01T13:56:14","slug":"the-flush-was-telling-the-truth","status":"publish","type":"post","link":"https:\/\/schindlerengineering.com\/public\/2026\/10\/01\/the-flush-was-telling-the-truth\/","title":{"rendered":"The flush was telling the truth"},"content":{"rendered":"

A post went live. The permalink worked. The front page — the URL people
\nactually type — showed no sign of it for two hours.<\/p>\n

\"Two<\/p>\n

Two of those three theories were about software we control, and both were
\ndocumented in our own code from previous incidents. A known bug is the most
\nseductive wrong answer there is: it explains the symptom, it comes with a
\ncitation, and it stops you looking.<\/p>\n

\"What<\/p>\n

The cache flush reported success every single time, and it was
\ntelling the truth<\/strong> — about the layer it owns. W3TC really
\nwas empty. The request simply never reached it, because the host runs an nginx
\nproxy cache in front of WordPress with a two-hour TTL.<\/p>\n

\"Three<\/p>\n

Nothing inside WordPress can see that layer, let alone clear it. But the
\nproxy accepts a purge:<\/p>\n

curl -X PURGE https:\/\/example.com\/   ->   204<\/pre>\n
The pipeline now runs flush WordPress → purge the proxy →
\nwarm the front doors<\/strong>, in that order. Warming before purging just
\nre-cements what the proxy is already holding.<\/p>\n
The one sentence<\/h2>\n
When a flush succeeds and the page is still wrong, you are flushing
\nthe wrong cache.<\/strong><\/p>\n
A flush can only report on the layer it owns. The response headers are a
\nreceipt from every layer that touched the request —
\nX-Proxy-Cache<\/code>, Age<\/code>, Via<\/code>,
\nX-Cache<\/code>, CF-Cache-Status<\/code>. We theorised for two hours
\nabout our own code; the answer was one curl -I<\/code> away, in software we
\ndid not know was there.<\/p>\n
Read the headers first. They do not have a theory.<\/p>\n","protected":false},"excerpt":{"rendered":"
A post went live. The permalink worked. The front page — the URL people actually type — showed no sign of it for two hours. Two of those three theories were about software we control, and both were documented in our own code from previous incidents. A known bug is the most seductive wrong answer … <\/p>\n
Continue reading “The flush was telling the truth”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-11115","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/schindlerengineering.com\/public\/wp-json\/wp\/v2\/posts\/11115","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/schindlerengineering.com\/public\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/schindlerengineering.com\/public\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/schindlerengineering.com\/public\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/schindlerengineering.com\/public\/wp-json\/wp\/v2\/comments?post=11115"}],"version-history":[{"count":1,"href":"https:\/\/schindlerengineering.com\/public\/wp-json\/wp\/v2\/posts\/11115\/revisions"}],"predecessor-version":[{"id":11116,"href":"https:\/\/schindlerengineering.com\/public\/wp-json\/wp\/v2\/posts\/11115\/revisions\/11116"}],"wp:attachment":[{"href":"https:\/\/schindlerengineering.com\/public\/wp-json\/wp\/v2\/media?parent=11115"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/schindlerengineering.com\/public\/wp-json\/wp\/v2\/categories?post=11115"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/schindlerengineering.com\/public\/wp-json\/wp\/v2\/tags?post=11115"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}