HTTP Caching Headers yaj

#http#performance#web

performance problems CDN pagh caching layer solve try law' actually wej HTTP headers (set correctly) free solve - apps law' accident wrong set (choice pagh). Cache-Control, ETag, Last-Modified browser resource re-fetch, cheaply re-validate, disk vo' instantly serve control - wej outcomes Dung difference configure Daq.

`Cache-Control`: qatlh header

Cache-Control browser (proxy CDN je) jatlh: response server contact pagh chay' long reuse laH.

Cache-Control: max-age=3600

meaning: 3600 seconds Dung server ask Qo' - cached copy reuse. window Dung request pagh, fastest possible outcome, server-side optimization law' nom (round trip pagh).

common directives:

max-age=<seconds> - response fresh long (browser cache perspective).
public - shared caches (CDNs, proxies) cache laH (browser neH pagh).
private - browser neH cache; shared CDN app qaSpa' Qo'.
no-cache - name 'ach caching allow, use Hoch server revalidation force (ETag bIngDaq). "never cache" vaD no-store.
no-store - cache pagh, nuqDaq. sensitive per-user data responses vaD right choice.

Cache-Control: private, no-store          # a user's account settings page
Cache-Control: public, max-age=31536000   # a hashed, versioned JS bundle
Cache-Control: no-cache                   # an HTML page you want revalidated every load

static assets `max-age` very long qatlh

build pipeline filenames content hash rap (app.a3f9c1.js, app.js pagh) - content choH vaj filename choH. specific file forever cache safe (new version new URL):

Cache-Control: public, max-age=31536000, immutable

immutable max-age law' signal: browser hard refresh Daq je revalidate pagh (content URL Daq choH laHbe'). hashed versioned filenames neH Dun - plain app.js overwritten in place Daq Qo' (deploy Hoch invisible already-loaded browsers).

revalidation: full re-download law' cheaper

resources choH 'ach cached poQ: max-age neH pagh - browser "actually choH'a'?" cheap check (blind re-download pagh). ETag 'ej Last-Modified 'oH.

app.get('/api/report/:id', async (req, res) => {
  const report = await getReport(req.params.id);
  const etag = `"${hashOf(report)}"`;

  res.set('ETag', etag);
  res.set('Cache-Control', 'no-cache');

  if (req.headers['if-none-match'] === etag) {
    return res.status(304).end(); // not modified — no body sent
  }

  res.json(report);
});

browser ETag nob If-None-Match header Daq next request Daq nob. match vaj server 304 Not Modified body pagh - browser cached copy reuse. no-cache "don't cache" pagh: "cache, check first" - check full response resend law' cheaper.

Last-Modified same, timestamp (hash pagh), If-Modified-Since:

res.set('Last-Modified', report.updatedAt.toUTCString());

if (req.headers['if-modified-since'] === report.updatedAt.toUTCString()) {
  return res.status(304).end();
}

ETag prefer (cheap hash response compute laH): precise (content change Hoch invalidate); Last-Modified second-level granularity neH, data modification times correctly track depend.

stack: realistic API response

Cache-Control: private, max-age=60, must-revalidate
ETag: "9f8c3a"

meaning: 60 seconds Dung cached copy reuse (ask pagh), window qaSDI' If-None-Match revalidate (304 pagh fresh data). authenticated API responses (occasionally choH, request Hoch pagh) default Dun - client server hammer pagh, minutes-old data stuck pagh.

"update pagh" bugs mistake

plain non-hashed filename Cache-Control: public, max-age=31536000 set: "fix deploy 'ach users old version legh" most common cause. browser content choH Sov laHbe' - URL identical, year ask Qo' jatlh. fix shorter max-age pagh: file filename content hash (real change real new URL) 'ej long max-age URLs neH reserve.

yaj

Cache-Control browser request send'a' decide. ETag/Last-Modified ask vaj server nearly-free 304 (body resend pagh) decide. long immutable caching content-hashed URLs neH; short max-age + revalidation stable URL Daq choH laH Hoch; no-store sensitive (cache Daq write pagh).