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Page: Jenkins and CI build cache for Gradle and Maven #21

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9e597fa
Page: Jenkins and CI build cache for Gradle and Maven
fosterstack-admin Oct 9, 2026
60d4551
CI page: the server has a read-only login; say so
fosterstack-admin Oct 9, 2026
4d4950b
CI page: a login, not the password
fosterstack-admin Oct 9, 2026
bd477b6
Owner cold-read edit: Maven stated without the in-progress hedge
fosterstack-admin Oct 9, 2026
7e3ae2c
Plain-HTTP wording: tested on Gradle 9.8.0, localhost name refused, 1…
fosterstack-admin Oct 9, 2026
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137 changes: 137 additions & 0 deletions jenkins-ci-build-cache/index.html
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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Jenkins and CI build cache for Gradle and Maven</title>
<meta name="description" content="Use one shared self-hosted build cache from Jenkins, GitHub Actions or GitLab runners: who should write, in-cluster setup, passwords, and how to check it works.">
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<div class="tag">Infrastructure worth keeping — and kept patched.</div>
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<main>
<h1>Jenkins and CI build cache for Gradle and Maven</h1>
<p class="lede">Point your Jenkins agents, GitHub Actions runners or GitLab runners at one shared build cache, so a fresh agent stops rebuilding what another agent already built.</p>

<h2>How a CI runner uses a remote build cache</h2>
<p>The cache is a plain web server. Your build tool (Gradle, or Maven with Apache's Build Cache Extension) asks it for finished task results and uploads new ones. Any runner that can reach the server over HTTP can use it. There is no plugin to install on the CI system.</p>
<p>We have not tested it with any particular CI product. Our own tests run in GitHub Actions. The protocol is the same everywhere, so what matters is that the runner can reach the server and holds a login.</p>

<h2>Let CI write, let developers read</h2>
<p>The simplest safe setup is that only CI uploads to the cache and laptops only download. The server can enforce this: give laptops the optional read-only login (<code>FSCACHE_RO_USERNAME</code> and <code>FSCACHE_RO_PASSWORD</code>), and any write they attempt is refused. On the Gradle side you can also stop uploads from non-CI machines in <code>settings.gradle.kts</code>:</p>
<pre><code>isPush = System.getenv("CI") != null</code></pre>
<p>That line alone is the client choosing not to upload, not a rule on the server. Anyone holding the read-write password can write, so share it only with people and systems you already trust to change your code.</p>

<h2>Runners inside your Kubernetes cluster</h2>
<p>If your runners already run in the cluster that hosts the cache (including Jenkins agents), you need no load balancer and no ingress. Point the build at the cluster-internal name:</p>
<pre><code>// FosterStack Cache — remote Gradle build cache.
// https://github.com/fosterstack/cache
buildCache {
remote&lt;HttpBuildCache&gt; {
url = uri("http://fscache.fscache-ns.svc.cluster.local/")
isAllowInsecureProtocol = true
isPush = true
credentials {
username = System.getenv("FSCACHE_USERNAME")
password = System.getenv("FSCACHE_PASSWORD")
}
}
}</code></pre>
<p>Replace <code>fscache-ns</code> with your namespace. Plain HTTP is acceptable here only because the traffic never leaves the cluster network. The manifests are in the <a href="https://github.com/fosterstack/cache/blob/main/docs/kubernetes.md">Kubernetes guide</a>.</p>

<h2>Runners outside the cluster, or on plain servers</h2>
<p>Run the server on a host the runners can reach and put HTTPS in front of it. Gradle sends the password with every request, so over plain HTTP it travels in the clear. Gradle refuses plain HTTP unless you opt in with <code>isAllowInsecureProtocol</code>, which is a useful warning, not a nuisance. (In our test with Gradle 9.8.0, the address <code>127.0.0.1</code> was allowed without it, but the name <code>localhost</code> was refused.) Setup is in the <a href="https://github.com/fosterstack/cache/blob/main/docs/install.md">install guide</a>.</p>

<h2>Give the runner the password</h2>
<p>Store it in your CI system's secret store and expose it as the <code>FSCACHE_PASSWORD</code> environment variable. On a long-lived agent, Gradle's background daemon reads its environment once, when it starts. If you change the secret and builds quietly stop using the cache, run <code>./gradlew --stop</code> so the next build starts a fresh daemon.</p>

<h2>Check that CI is really using the cache</h2>
<p>Run the same build twice on two different agents. The second should show <code>FROM-CACHE</code> next to tasks. A runner's local cache can hide a broken remote, so run once with <code>-i</code>, which prints remote errors. Gradle treats a broken remote as non-fatal, so it fails silently otherwise. On the server, the hit and miss counters at <code>/metrics</code> should move.</p>
<p>Maven on CI follows the same pattern with the extension and a <code>&lt;server&gt;</code> entry for the password. See the <a href="/migrate-build-cache-node/">Gradle and Maven setup page</a>.</p>

<div class="cta-row">
<a class="btn" href="/migrate-build-cache-node/">Gradle and Maven setup</a>
<a class="btn btn-secondary" href="/">FosterStack home</a>
</div>
</main>
<footer>
<div>
<p>FosterStack is not affiliated with, endorsed by, or sponsored by Gradle Inc.
"Gradle" and "Develocity" are trademarks of Gradle Inc., used here only to identify
compatibility. FosterStack contains no Gradle Inc. code; it is a clean-room implementation
of the documented remote build cache HTTP protocol. Apache Maven is a trademark of the
Apache Software Foundation; the Maven Build Cache Extension is Apache's project, not
ours.</p>
<p style="margin-top:.6rem">© 2026 FosterStack · <a href="/regulated/">For regulated markets</a> · <a href="https://github.com/fosterstack/cache">github.com/fosterstack/cache</a> · <a href="mailto:hello@fosterstack.com">hello@fosterstack.com</a></p>
</div>
</footer>
</body>
</html>
4 changes: 4 additions & 0 deletions sitemap.xml
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<changefreq>weekly</changefreq>
<priority>1.0</priority>
</url>
<url>
<loc>https://fosterstack.com/jenkins-ci-build-cache/</loc>
<lastmod>2026-10-08</lastmod>
</url>
</urlset>
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