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<h1 class="post-title-main">MQTT 3.1.1 protocol binding</h1>
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<p>Consume messages from MQTT brokers via <a href="#source-format">sources</a> and send messages to MQTT brokers via
<a href="#target-format">targets</a>.</p>
<h2 id="content-type">Content-type</h2>
<p>When MQTT messages are sent in <a href="protocol-overview.html">Ditto Protocol</a>,
the payload should be <code class="highlighter-rouge">UTF-8</code> encoded strings.</p>
<p>If messages which are not in Ditto Protocol should be processed, a <a href="connectivity-mapping.html">payload mapping</a> must
be configured for the connection in order to transform the messages.</p>
<h2 id="mqtt-311-properties">MQTT 3.1.1 properties</h2>
<p>MQTT 3.1.1 messages have no application headers. Transmission-relevant properties are set in the
<code class="highlighter-rouge">"headers"</code> field as a part of <a href="protocol-specification.html#dittoProtocolEnvelope">Ditto protocol messages</a> in the
payload.</p>
<p>This property is supported:</p>
<ul>
<li><code class="highlighter-rouge">correlation-id</code>: For correlating request messages and events. Twin events have the correlation IDs of
<a href="protocol-twinlive.html#twin">Twin commands</a> that produced them.</li>
</ul>
<h2 id="specific-connection-configuration">Specific connection configuration</h2>
<p>The common configuration for connections in <a href="basic-connections.html#sources">Connections &gt; Sources</a> and
<a href="basic-connections.html#targets">Connections &gt; Targets</a> applies here as well.
Following are some specifics for MQTT connections:</p>
<h3 id="source-format">Source format</h3>
<p>For an MQTT connection:</p>
<ul>
<li>Source <code class="highlighter-rouge">"addresses"</code> are MQTT topics to subscribe to. Wildcards <code class="highlighter-rouge">+</code> and <code class="highlighter-rouge">#</code> are allowed.</li>
<li><code class="highlighter-rouge">"authorizationContext"</code> may <em>not</em> contain placeholders <code class="highlighter-rouge">{{ header:&lt;header-name&gt; }}</code> as MQTT 3.1.1
has no application headers.</li>
<li>The optional field <code class="highlighter-rouge">"qos"</code> sets the maximum Quality of Service to request when subscribing for messages. Its value
can be <code class="highlighter-rouge">0</code> for at-most-once delivery, <code class="highlighter-rouge">1</code> for at-least-once delivery and <code class="highlighter-rouge">2</code> for exactly-once delivery.
The default value is <code class="highlighter-rouge">2</code> (exactly-once).
Support of any Quality of Service depends on the external MQTT broker; <a href="https://docs.aws.amazon.com/iot/">AWS IoT</a> for example does not
acknowledge subscriptions with <code class="highlighter-rouge">qos=2</code>.</li>
</ul>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"addresses"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w">
</span><span class="s2">"&lt;mqtt_topic&gt;"</span><span class="p">,</span><span class="w">
</span><span class="s2">"..."</span><span class="w">
</span><span class="p">],</span><span class="w">
</span><span class="s2">"authorizationContext"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"ditto:inbound-auth-subject"</span><span class="p">,</span><span class="w"> </span><span class="s2">"..."</span><span class="p">],</span><span class="w">
</span><span class="s2">"qos"</span><span class="p">:</span><span class="w"> </span><span class="mi">2</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>Note: This example assumes that there is a valid user named <code class="highlighter-rouge">ditto:inbound-auth-subject</code> in Ditto.
If you want to use a user for the basic auth (from the <a href="connectivity-protocol-bindings-http.html">HTTP API</a>) use the prefix <code class="highlighter-rouge">nginx:</code>, e.g. <code class="highlighter-rouge">nginx:ditto</code>.
See <a href="basic-auth.html#authorization-context-in-devops-commands">Basic Authentication</a> for more information.</p>
<h4 id="enforcement">Enforcement</h4>
<p>As MQTT 3.1.1 does not support headers in its protocol, headers may not be used during <a href="basic-connections.html#source-enforcement">source enforcement</a>.</p>
<h4 id="source-header-mapping">Source header mapping</h4>
<p>As MQTT 3.1.1 does not support headers in its protocol, it is not possible to configure a <a href="connectivity-header-mapping.html">header mapping</a> here.</p>
<h3 id="target-format">Target format</h3>
<p>For an MQTT connection, the target address is the MQTT topic to publish events and messages to.
The target address may contain placeholders; see
<a href="basic-connections.html#placeholder-for-target-addresses">placeholders</a> section for more information.</p>
<p>Further, <code class="highlighter-rouge">"topics"</code> is a list of strings, each list entry representing a subscription of
<a href="protocol-specification-topic.html">Ditto protocol topics</a>.</p>
<p>Outbound messages are published to the configured target address if one of the subjects in <code class="highlighter-rouge">"authorizationContext"</code>
has READ permission on the Thing, that is associated with a message.</p>
<p>The additional field <code class="highlighter-rouge">"qos"</code> sets the Quality of Service with which messages are published.
Its value can be <code class="highlighter-rouge">0</code> for at-most-once delivery, <code class="highlighter-rouge">1</code> for at-least-once delivery and <code class="highlighter-rouge">2</code> for exactly-once delivery.
Support of any Quality of Service depends on the external MQTT broker.
The default value is <code class="highlighter-rouge">0</code> (at-most-once).</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"address"</span><span class="p">:</span><span class="w"> </span><span class="s2">"mqtt/topic/of/my/device/{{ thing:id }}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"topics"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w">
</span><span class="s2">"_/_/things/twin/events"</span><span class="p">,</span><span class="w">
</span><span class="s2">"_/_/things/live/messages"</span><span class="w">
</span><span class="p">],</span><span class="w">
</span><span class="s2">"authorizationContext"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"ditto:outbound-auth-subject"</span><span class="p">,</span><span class="w"> </span><span class="s2">"..."</span><span class="p">],</span><span class="w">
</span><span class="s2">"qos"</span><span class="p">:</span><span class="w"> </span><span class="mi">0</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<h4 id="target-header-mapping">Target header mapping</h4>
<p>As MQTT 3.1.1 does not support headers in its protocol, a <a href="connectivity-header-mapping.html">header mapping</a> is not possible to configure here.</p>
<h3 id="specific-config">Specific Config</h3>
<p>The MQTT binding offers an additional <a href="basic-connections.html#specific-config">specific configuration</a> for the mqtt client id. If the
<code class="highlighter-rouge">clientId</code> is not configured as a <a href="basic-connections.html#specific-config">specific config</a> Ditto will use the <code class="highlighter-rouge">connection-id</code> as <code class="highlighter-rouge">clientId</code>
for the outgoing mqtt connection.</p>
<p>Example</p>
<p>Defining the client id <code class="highlighter-rouge">my-awesome-mqtt-client-id</code>:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"id"</span><span class="p">:</span><span class="w"> </span><span class="s2">"mqtt-example-connection-123"</span><span class="p">,</span><span class="w">
</span><span class="s2">"connectionType"</span><span class="p">:</span><span class="w"> </span><span class="s2">"mqtt"</span><span class="p">,</span><span class="w">
</span><span class="s2">"connectionStatus"</span><span class="p">:</span><span class="w"> </span><span class="s2">"open"</span><span class="p">,</span><span class="w">
</span><span class="s2">"failoverEnabled"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w">
</span><span class="s2">"uri"</span><span class="p">:</span><span class="w"> </span><span class="s2">"tcp://test.mosquitto.org:1883"</span><span class="p">,</span><span class="w">
</span><span class="s2">"specificConfig"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"clientId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"my-awesome-mqtt-client-id"</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"sources"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"..."</span><span class="p">],</span><span class="w">
</span><span class="s2">"targets"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"..."</span><span class="p">]</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<h2 id="establishing-a-connection-to-an-mqtt-311-endpoint">Establishing a connection to an MQTT 3.1.1 endpoint</h2>
<p>Ditto’s <a href="architecture-services-connectivity.html">Connectivity service</a> is responsible for creating new and managing
existing connections.</p>
<p>This can be done dynamically at runtime without the need to restart any microservice using a
<a href="installation-operating.html#devops-commands">Ditto DevOps command</a>.</p>
<p>Example</p>
<p>Connection configuration to create a new MQTT connection:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"id"</span><span class="p">:</span><span class="w"> </span><span class="s2">"mqtt-example-connection-123"</span><span class="p">,</span><span class="w">
</span><span class="s2">"connectionType"</span><span class="p">:</span><span class="w"> </span><span class="s2">"mqtt"</span><span class="p">,</span><span class="w">
</span><span class="s2">"connectionStatus"</span><span class="p">:</span><span class="w"> </span><span class="s2">"open"</span><span class="p">,</span><span class="w">
</span><span class="s2">"failoverEnabled"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w">
</span><span class="s2">"uri"</span><span class="p">:</span><span class="w"> </span><span class="s2">"tcp://test.mosquitto.org:1883"</span><span class="p">,</span><span class="w">
</span><span class="s2">"sources"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w">
</span><span class="p">{</span><span class="w">
</span><span class="s2">"addresses"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w">
</span><span class="s2">"eclipse-ditto-sandbox/#"</span><span class="w">
</span><span class="p">],</span><span class="w">
</span><span class="s2">"authorizationContext"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"ditto:inbound-auth-subject"</span><span class="p">],</span><span class="w">
</span><span class="s2">"qos"</span><span class="p">:</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
</span><span class="s2">"filters"</span><span class="p">:</span><span class="w"> </span><span class="p">[]</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">],</span><span class="w">
</span><span class="s2">"targets"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w">
</span><span class="p">{</span><span class="w">
</span><span class="s2">"address"</span><span class="p">:</span><span class="w"> </span><span class="s2">"eclipse-ditto-sandbox/{{ thing:id }}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"topics"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w">
</span><span class="s2">"_/_/things/twin/events"</span><span class="w">
</span><span class="p">],</span><span class="w">
</span><span class="s2">"authorizationContext"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"ditto:outbound-auth-subject"</span><span class="p">],</span><span class="w">
</span><span class="s2">"qos"</span><span class="p">:</span><span class="w"> </span><span class="mi">0</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">]</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<h2 id="client-certificate-authentication">Client-certificate authentication</h2>
<p>Ditto supports certificate-based authentication for MQTT connections. Consult
<a href="connectivity-tls-certificates.html">Certificates for Transport Layer Security</a>
for how to set it up.</p>
<p>Here is an example MQTT connection that checks the broker certificate and authenticates by a client certificate.</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"id"</span><span class="p">:</span><span class="w"> </span><span class="s2">"mqtt-example-connection-124"</span><span class="p">,</span><span class="w">
</span><span class="s2">"connectionType"</span><span class="p">:</span><span class="w"> </span><span class="s2">"mqtt"</span><span class="p">,</span><span class="w">
</span><span class="s2">"connectionStatus"</span><span class="p">:</span><span class="w"> </span><span class="s2">"open"</span><span class="p">,</span><span class="w">
</span><span class="s2">"failoverEnabled"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w">
</span><span class="s2">"uri"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ssl://test.mosquitto.org:8884"</span><span class="p">,</span><span class="w">
</span><span class="s2">"validateCertificates"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w">
</span><span class="s2">"ca"</span><span class="p">:</span><span class="w"> </span><span class="s2">"-----BEGIN CERTIFICATE-----</span><span class="se">\n</span><span class="s2">&lt;test.mosquitto.org certificate&gt;</span><span class="se">\n</span><span class="s2">-----END CERTIFICATE-----"</span><span class="p">,</span><span class="w">
</span><span class="s2">"credentials"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"type"</span><span class="p">:</span><span class="w"> </span><span class="s2">"client-cert"</span><span class="p">,</span><span class="w">
</span><span class="s2">"cert"</span><span class="p">:</span><span class="w"> </span><span class="s2">"-----BEGIN CERTIFICATE-----</span><span class="se">\n</span><span class="s2">&lt;signed client certificate&gt;</span><span class="se">\n</span><span class="s2">-----END CERTIFICATE-----"</span><span class="p">,</span><span class="w">
</span><span class="s2">"key"</span><span class="p">:</span><span class="w"> </span><span class="s2">"-----BEGIN PRIVATE KEY-----</span><span class="se">\n</span><span class="s2">&lt;client private key&gt;</span><span class="se">\n</span><span class="s2">-----END PRIVATE KEY-----"</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"sources"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w">
</span><span class="p">{</span><span class="w">
</span><span class="s2">"addresses"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w">
</span><span class="s2">"eclipse-ditto-sandbox/#"</span><span class="w">
</span><span class="p">],</span><span class="w">
</span><span class="s2">"authorizationContext"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"ditto:inbound-auth-subject"</span><span class="p">],</span><span class="w">
</span><span class="s2">"qos"</span><span class="p">:</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
</span><span class="s2">"filters"</span><span class="p">:</span><span class="w"> </span><span class="p">[]</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">],</span><span class="w">
</span><span class="s2">"targets"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w">
</span><span class="p">{</span><span class="w">
</span><span class="s2">"address"</span><span class="p">:</span><span class="w"> </span><span class="s2">"eclipse-ditto-sandbox/{{ thing:id }}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"topics"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="w">
</span><span class="s2">"_/_/things/twin/events"</span><span class="w">
</span><span class="p">],</span><span class="w">
</span><span class="s2">"authorizationContext"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"ditto:outbound-auth-subject"</span><span class="p">],</span><span class="w">
</span><span class="s2">"qos"</span><span class="p">:</span><span class="w"> </span><span class="mi">0</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">]</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
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