<p>We are using <a href="https://github.com/uber/kraken" rel="nofollow noreferrer">Uber Kraken</a> to increase container download speeds in a kubernetes cluster, it works great.</p>
<p>However, we commonly mutate tags (upload a new version of <code>:latest</code>). In the <a href="https://github.com/uber/kraken#limitations" rel="nofollow noreferrer">limitations section of the Uber Kraken Github page</a> they state:</p>
<blockquote>
<p>Mutating tags (e.g. updating a latest tag) is allowed, however, a few things will not work: tag lookups immediately afterwards will still return the old value due to Nginx caching, and replication probably won't trigger. We are working on supporting this functionality better. If you need tag mutation support right now, please <strong>reduce the cache interval of the build-index component</strong>. If you also need replication in a multi-cluster setup, please consider setting up another Docker registry as Kraken's backend.</p>
</blockquote>
<p>What do they mean by <em>&quot;reduce the cache interval of the build-index component&quot;</em>? I don't quite understand what they are referring to in the docker universe.</p>

<p>This sentence comes from <a href="https://github.com/uber/kraken/pull/61/files" rel="nofollow noreferrer">PR 61</a>.</p>
<p>It offers a better alternative than the previous documentation, which stated:</p>
<blockquote>
<p>Mutating tags is allowed, however the behavior is undefined.<br />
A few things will go wrong:</p>
<ul>
<li>replication probably won't trigger, and</li>
<li>most tag lookups will probably still return the old tag due to caching.</li>
</ul>
<p>We are working supporting this functionality better.<br />
If you need mutation (e.g. updating a latest tag) right now, please consider implementing your own index component on top of a consistent key-value store.</p>
</blockquote>
<p>That last sentence was before:</p>
<blockquote>
<p>please consider setting up another docker registry as Kraken's backend,
and reduce cache interval of build-index component</p>
</blockquote>
<p>That would replace the current <a href="https://github.com/uber/kraken/blob/59fa7bcab998ca1abb7a2c268017db240cb0835e/docs/CONFIGURATION.md#configuring-storage-backend-for-origin-and-build-index" rel="nofollow noreferrer">Storage Backend For Origin And Build-Index</a>.</p>
