posts-go/docs/2022-10-26-reload-config.html

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<h2>
<a href="index.html"><code>~</code></a>
</h2>
<h1 id="user-content-reload-config">
<a class="heading-link" href="#reload-config"
>Reload config<span
aria-hidden="true"
class="octicon octicon-link"
></span
></a>
</h1>
<p>This serves as design draft of reload config system</p>
<div class="highlight highlight-source-wsd">
<pre><span class="pl-k">@startuml</span> Reload config
<span class="pl-k">skinparam</span> <span class="pl-k">defaultFontName</span> <span class="pl-s">Iosevka Term SS08</span>
<span class="pl-k">participant</span> <span class="pl-c1">admin</span>
<span class="pl-k">participant</span> <span class="pl-c1">other_service</span>
<span class="pl-k">participant</span> <span class="pl-c1">config_service</span>
<span class="pl-k">participant</span> <span class="pl-c1">storage</span>
<span class="pl-k">==</span> <span class="pl-s">Admin handle</span> <span class="pl-k">==</span>
<span class="pl-c1">admin</span> <span class="pl-k">-&gt;</span> <span class="pl-c1">config_service</span>: set/update/delete config
<span class="pl-c1">config_service</span> <span class="pl-k">-&gt;</span> <span class="pl-c1">storage</span>: set/update/delete config
<span class="pl-k">==</span> <span class="pl-s">Other service handle</span> <span class="pl-k">==</span>
<span class="pl-c1">other_service</span> <span class="pl-k">-&gt;</span> <span class="pl-c1">other_service</span>: init service
<span class="pl-k">activate</span> <span class="pl-c1">other_service</span>
<span class="pl-c1">other_service</span> <span class="pl-k">-&gt;</span> <span class="pl-c1">storage</span>: make connection
<span class="pl-k">loop</span>
<span class="pl-c1">other_service</span> <span class="pl-k">-&gt;</span> <span class="pl-c1">storage</span>: listen on config change
<span class="pl-c1">other_service</span> <span class="pl-k">-&gt;</span> <span class="pl-c1">other_service</span>: save config to memory
<span class="pl-k">end</span>
<span class="pl-k">deactivate</span> <span class="pl-c1">other_service</span>
<span class="pl-c1">other_service</span> <span class="pl-k">-&gt;</span> <span class="pl-c1">other_service</span>: do business
<span class="pl-k">activate</span> <span class="pl-c1">other_service</span>
<span class="pl-c1">other_service</span> <span class="pl-k">-&gt;</span> <span class="pl-c1">other_service</span>: get config
<span class="pl-c1">other_service</span> <span class="pl-k">-&gt;</span> <span class="pl-c1">other_service</span>: do other business
<span class="pl-k">deactivate</span> <span class="pl-c1">other_service</span>
<span class="pl-k">@enduml</span></pre>
</div>
<p>
Config storage can be any key value storage or database like etcd, Consul,
mySQL, ...
</p>
<p>
If storage is key value storage, maybe there is API to listen on config
change. Otherwise we should create a loop to get all config from storage
for some interval, for example each 5 minute.
</p>
<p>
Each <code>other_service</code> need to get config from its memory, not
hit <code>storage</code>. So there is some delay between upstream config
(config in <code>storage</code>) and downstream config (config in
<code>other_service</code>), but maybe we can forgive that delay (???).
</p>
<p>Pros:</p>
<ul>
<li>
<p>
Config can be dynamic, service does not need to restart to apply new
config.
</p>
</li>
<li>
<p>
Each service only keep 1 connection to <code>storage</code> to listen
to config change, not hit <code>storage</code> for each request.
</p>
</li>
</ul>
<p>Cons:</p>
<ul>
<li>Each service has 1 more dependency, aka <code>storage</code>.</li>
<li>
Need to handle fallback config, incase <code>storage</code> failure.
</li>
<li>Delay between upstream/downstream config</li>
</ul>
<div>
Feel free to ask me via
<a href="mailto:hauvipapro+posts@gmail.com">email</a> or
<a rel="me" href="https://hachyderm.io/@haunguyen">Mastodon</a>.
<br />Source code is available on
<a href="https://github.com/haunt98/posts-go">GitHub</a>
<a href="https://codeberg.org/yoshie/posts-go">Codeberg</a>
<a href="https://git.sr.ht/~youngyoshie/posts-go">sourcehut</a>
<a href="https://gitea.treehouse.systems/yoshie/posts-go">Treehouse</a>
<a href="https://gitlab.com/youngyoshie/posts-go">GitLab</a>
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