home-assistant.github.io/architecture/index.html
2014-12-21 15:25:40 -08:00

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Architecture
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<p><a href='/images/ha_architecture.png'>
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<p>The core of Home Assistant exists of the following parts.</p>
<p>The <strong>Event Bus</strong> facilitates the firing and listening of events. This is the beating heart of Home Assistant.</p>
<p>The <strong>State Machine</strong> keeps track of the states of things. Fires a state_changed event when a state has been changed.</p>
<p>The <strong>Service Registry</strong> listens on the event bus for call_service events and allows other code to register services.</p>
<p>The <strong>Timer</strong> will send every 10 seconds a time_changed event on the event bus.</p>
<p>Take for example the device_tracker component. This component is responsible for keeping track which devices are home. It checks which devices are home every time a time_changed event is fired on the event bus. It will then update the state machine with the information for each device.</p>
<p>This setup allows us to create simple yet powerful logic for controlling your home:</p>
<pre><code>In the event that device 'Paulus Nexus 5' changes to the 'Home' state:
If the sun has set and the lights are not on:
Turn on the lights
In the event that the combined state of all tracked devices changes to 'Not Home':
If the lights are on:
Turn off the lights
In the event of the sun setting:
If the lights are off and the combined state of all tracked device equals 'Home':
Turn on the lights
</code></pre>
<p>By using the Bus as a central communication hub between components it is easy to replace components or add functionality. If you would want to change the way devices are detected you only have to write a component that updates the device states in the State Machine.</p>
<h2>Multiple connected instances</h2>
<p>Home Assistant supports running multiple synchronzied instances using a master-slave model. Slaves forward all local events fired and states set to the master instance which will then replicate it to each slave.</p>
<p>Because each slave maintains its own ServiceRegistry it is possible to have multiple slaves respond to one service call.</p>
<p><a href='/images/architecture-remote.png'>
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<p>A slave instance can be started with the following code and has the same support for components as a master-instance.</p>
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</pre></td><td class='code'><pre><code class='python'><span class='line'><span class="kn">import</span> <span class="nn">homeassistant.remote</span> <span class="kn">as</span> <span class="nn">remote</span>
</span><span class='line'><span class="kn">import</span> <span class="nn">homeassistant.components.http</span> <span class="kn">as</span> <span class="nn">http</span>
</span><span class='line'>
</span><span class='line'><span class="n">remote_api</span> <span class="o">=</span> <span class="n">remote</span><span class="o">.</span><span class="n">API</span><span class="p">(</span><span class="s">&quot;remote_host_or_ip&quot;</span><span class="p">,</span> <span class="s">&quot;remote_api_password&quot;</span><span class="p">)</span>
</span><span class='line'>
</span><span class='line'><span class="n">hass</span> <span class="o">=</span> <span class="n">remote</span><span class="o">.</span><span class="n">HomeAssistant</span><span class="p">(</span><span class="n">remote_api</span><span class="p">)</span>
</span><span class='line'>
</span><span class='line'><span class="n">http</span><span class="o">.</span><span class="n">setup</span><span class="p">(</span><span class="n">hass</span><span class="p">,</span> <span class="s">&quot;my_local_api_password&quot;</span><span class="p">)</span>
</span><span class='line'>
</span><span class='line'><span class="n">hass</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
</span><span class='line'><span class="n">hass</span><span class="o">.</span><span class="n">block_till_stopped</span><span class="p">()</span>
</span></code></pre></td></tr></table></div></figure>
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