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    <h2>
      <a href="index.html"><code>~</code></a>
    </h2>
    <div class="markdown-heading">
      <h1 class="heading-element">Reload config</h1>
      <a
        id="user-content-reload-config"
        class="anchor"
        aria-label="Permalink: Reload config"
        href="#reload-config"
        ><span aria-hidden="true" class="octicon octicon-link"></span
      ></a>
    </div>
    <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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