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| </ul> |
| </li> |
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| <li class="subfolders"> |
| <a href="#"><span></span>→ Things merge examples</a> |
| <ul> |
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| <li><a href="protocol-examples-mergething.html">Merge a Thing</a></li> |
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| <li><a href="protocol-examples-mergepolicyid.html">Merge the Policy ID of a Thing</a></li> |
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| <li><a href="protocol-examples-mergeattributes.html">Merge Attributes</a></li> |
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| <li><a href="protocol-examples-mergeattribute.html">Merge a single Attribute</a></li> |
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| <li><a href="protocol-examples-mergedesiredproperties.html">Merge desired Feature Properties</a></li> |
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| <li><a href="protocol-examples-errorresponses.html">Error responses</a></li> |
| |
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| </ul> |
| </li> |
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| <li class="subfolders"> |
| <a href="#"><span></span>→ Policies examples</a> |
| <ul> |
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| <li><a href="protocol-examples-policies-createpolicy.html">Create a Policy</a></li> |
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| <li><a href="protocol-examples-policies-deletepolicy.html">Delete a Policy</a></li> |
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| <li><a href="protocol-examples-policies-modifypolicy.html">Modify a Policy</a></li> |
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| <li><a href="protocol-examples-policies-retrievepolicy.html">Retrieve a Policy</a></li> |
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| <li><a href="protocol-examples-policies-modifypolicyentries.html">Modify entries</a></li> |
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| <li><a href="protocol-examples-policies-retrievepolicyentries.html">Retrieve entries</a></li> |
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| <li><a href="protocol-examples-policies-createpolicyentry.html">Create a single entry</a></li> |
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| <li><a href="protocol-examples-policies-deletepolicyentry.html">Delete a single entry</a></li> |
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| <li><a href="protocol-examples-policies-modifypolicyentry.html">Modify a single entry</a></li> |
| |
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| <li><a href="protocol-examples-policies-retrievepolicyentry.html">Retrieve a single entry</a></li> |
| |
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| <li><a href="protocol-examples-policies-modifysubjects.html">Modify subjects</a></li> |
| |
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| <li><a href="protocol-examples-policies-retrievesubjects.html">Retrieve subjects</a></li> |
| |
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| <li><a href="protocol-examples-policies-createsubject.html">Create a single subject</a></li> |
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| <li><a href="protocol-examples-policies-deletesubject.html">Delete a single subject</a></li> |
| |
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| <li><a href="protocol-examples-policies-modifysubject.html">Modify a single subject</a></li> |
| |
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| <li><a href="protocol-examples-policies-retrievesubject.html">Retrieve a single subject</a></li> |
| |
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| <li><a href="protocol-examples-policies-modifyresources.html">Modify resources</a></li> |
| |
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| <li><a href="protocol-examples-policies-retrieveresources.html">Retrieve resources</a></li> |
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| <li><a href="protocol-examples-policies-createresource.html">Create a single resource</a></li> |
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| <li><a href="protocol-examples-policies-deleteresource.html">Delete a single resource</a></li> |
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| <li><a href="protocol-examples-policies-modifyresource.html">Modify a single resource</a></li> |
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| <li><a href="protocol-examples-policies-retrieveresource.html">Retrieve a single resource</a></li> |
| |
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| <li><a href="protocol-examples-policies-errorresponses.html">Error responses</a></li> |
| |
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| <li><a href="protocol-examples-policies-announcement-subjectDeletion.html">Announcement for subject deletion</a></li> |
| |
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| |
| </ul> |
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| <h1 class="post-title-main">Data By-Pass Pattern</h1> |
| </div> |
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| <div class="post-content"> |
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| <p>This pattern centers around the idea to delegate the data transmission to external services, by-passing the Ditto cluster, |
| while still being able to benefit from Ditto’s <a href="basic-policy.html">policy system</a> and IoT architecture.</p> |
| |
| <h2 id="context">Context</h2> |
| |
| <p>You have services exposing their functionality transparently though Ditto’s messaging API as part of your digital twin. |
| E.g. a history service providing the actual interface to your timeseries database as part of the things interface such |
| that a client may not need to know if the history actually is managed by the thing itself or any other program. |
| You use Ditto’s <a href="basic-policy.html">policy system</a> to secure access to your services that way.</p> |
| |
| <p>Your services provide data in quantities that are not suited for transmission through the Ditto cluster directly, |
| because of (de-)serialization costs, round-trip-times etc.</p> |
| |
| <h2 id="problem">Problem</h2> |
| |
| <p>You want to query a greater amount of data (e.g. database query result) by issuing a Ditto message to a thing which is |
| picked up by a service speaking with you databases. It does not work to just let this service return the result |
| as a response to the Ditto message, since the messaging system in the Ditto cluster is not designed for big quantities |
| of data and will reject them based on tight quotas. Also the costs due to many (de-)serialization steps are high.</p> |
| |
| <h2 id="solution">Solution</h2> |
| |
| <p>The solution consists of the following systems:</p> |
| |
| <ul> |
| <li><strong>database</strong>: where your bigger chunks of data reside and wait to be delivered / queried</li> |
| <li><strong>database provider mirco-service</strong>: the service managing the database connection and exposing it to clients through |
| things messaging API</li> |
| <li><strong>thing</strong>: a digital twin with extended API through a micro-service</li> |
| <li><strong>client</strong>: a client-application trying to receive bigger quantities of data via a things messaging API in the scope |
| of that thing and secured via ditto policies</li> |
| <li><strong>high-performance data proxy</strong> (or just proxy): a third-party application proxy sitting in-between the database and |
| the provider micro-service managing data delivery</li> |
| </ul> |
| |
| <figure><img class="docimage" src="images/pages/advanced/data-by-pass-architectural-design.jpg" alt="Architectural Design" style="max-width: 800px" /><figcaption>Architectural design of the data by-pass pattern showing all actors and their interactions.</figcaption></figure> |
| |
| <p>In order for the client-application to retrieve the requested data in a secure and performant way we introduce a |
| high-performance proxy (e.g. based on nginx, example below). The proxy will not have any credentials by itself, |
| it’s just serving prepared queries on a randomly, hard-to-guess URL with an expiration time of 5 minutes. |
| It features an admin API which the micro-service has credentials to access.</p> |
| |
| <p>The provider micro-service hooks into a twin (e.g. via websockets) and listens for queries. |
| If a query arrives it will formulate the query, store it at the high-performance proxy (which might already query the data) |
| and return a randomly generated URL to the proxy together with a Location-header as a response to the client-application. |
| The client then needs to follow the response in order to retrieve the data from the proxy.</p> |
| |
| <p>With this approach the access to the database is secured via Ditto <a href="basic-policy.html">policies</a> and in scope of single |
| things while the data retrieval happens via a performant proxy application without the Ditto cluster ever seeing those packages.</p> |
| |
| <p><em>Note: Keep in mind that security in this situation is highly dependent of the micro-service implementation. |
| You have to make sure that your implementation uses provided information of ditto properly and that the contents of |
| a message do not allow a violation of the policy. E.g. through SQL-Injections.</em></p> |
| |
| <h2 id="discussion">Discussion</h2> |
| |
| <p><strong>Benefits</strong>:</p> |
| |
| <ul> |
| <li>Higher performance compared to using just Ditto</li> |
| <li>The Ditto <a href="basic-policy.html">policy system</a> can be utilized to scope and secure data access from clients to databases/-stores</li> |
| </ul> |
| |
| <p><strong>Drawbacks</strong>:</p> |
| |
| <ul> |
| <li>A third-party application for the high-performance proxy has to be added and maintained</li> |
| <li>A custom messaging API is necessary in the first place introducing a higher complexity</li> |
| <li>A translation of certain query-languages from messages to the actual databases / applications has to be implemented</li> |
| </ul> |
| |
| <p><strong>Issues</strong>:</p> |
| |
| <ul> |
| <li>Managing and communicating custom messaging APIs is not natively supported in Ditto, other ways have to be explored to |
| keep APIs consistent</li> |
| </ul> |
| |
| <h2 id="policies">Policies</h2> |
| |
| <p>Policies can be used to restrict access to the provider micro-service and through that eventually to the database using |
| restrictions on the <code class="highlighter-rouge">message:/</code> resource.</p> |
| |
| <p>Let’s assume that the provider micro-service registers via websockets and expects requests to the message-topic |
| <code class="highlighter-rouge">/services/history</code>. With the following policy entry we can allow access to this resource:</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">"subjects"</span><span class="p">:</span><span class="w"> </span><span class="p">{},</span><span class="w"> |
| </span><span class="s2">"resources"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w"> |
| </span><span class="s2">"message:/"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w"> |
| </span><span class="s2">"grant"</span><span class="p">:</span><span class="w"> </span><span class="p">[],</span><span class="w"> |
| </span><span class="s2">"revoke"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"READ"</span><span class="p">,</span><span class="w"> </span><span class="s2">"WRITE"</span><span class="p">]</span><span class="w"> |
| </span><span class="p">},</span><span class="w"> |
| </span><span class="s2">"message:/inbox/messages/services/history"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w"> |
| </span><span class="s2">"grant"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"READ"</span><span class="p">],</span><span class="w"> |
| </span><span class="s2">"revoke"</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">"message:/outbox/messages/services/history"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w"> |
| </span><span class="s2">"grant"</span><span class="p">:</span><span class="w"> </span><span class="p">[</span><span class="s2">"WRITE"</span><span class="p">],</span><span class="w"> |
| </span><span class="s2">"revoke"</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="p">}</span><span class="w"> |
| </span></code></pre></div></div> |
| |
| <p>The first resource entry revokes any access to messages for subjects of this type. This is optional. The next entry |
| allows the provider micro-service to read messages from the topic <code class="highlighter-rouge">/services/history</code>. Note that we’ve decided to insert |
| another “namespace” <code class="highlighter-rouge">/services</code> here to distinguish these messages from other device faced messages. The last section |
| than allows the provider micro-service to reply to the received requests with it’s 303 response.</p> |
| |
| <p>This can also be built against single features. Since features have to be stated explicitly in the policy, this is not |
| as general but can provide a more fine-grained access control when using distinct policies for different things, |
| or features with same names over multiple things.</p> |
| |
| <h2 id="proxy-implementations">Proxy Implementations</h2> |
| |
| <p>The <a href="https://github.com/sourcelair/ceryx">ceryx proxy project</a> was used for the |
| <a href="https://github.com/w4tsn/ceryx">PoC (or reference implementation)</a> of this pattern. |
| It was enhanced with delegation features which still have to be contributed upstream. |
| Have a look at the <a href="https://github.com/w4tsn/ceryx">forks source code</a> or |
| the <a href="https://quay.io/repository/w4tsn/ceryx">corresponding container image</a> until then.</p> |
| |
| <p>The ceryx proxy is a modified nginx with a redis-database to store the randomly generated IDs correlating with prepared queries. |
| It is not suited for this use-case on its own so capabilities to store queries (including Authentication) behind |
| expiring random URLs was added, but not send upstream yet.</p> |
| |
| <h2 id="known-uses">Known uses</h2> |
| |
| <p><strong><a href="https://www.othermo.de">othermo GmbH</a> uses this for a history-service</strong>: The history service connects to Ditto via |
| websockets and hooks into things by answering specific <code class="highlighter-rouge">/history</code> messages. The messages API is translated to InfluxDB queries |
| which then are stored with a randomly generated URL and expiration of 5 minutes at the high-performance proxy. |
| The service then returns the random URL to the client which then follows the 303 to retrieve the actual data.</p> |
| |
| <p>The messages contain InfluxDB-similar query elements while the query is only constructed at the provider service. |
| That’s because the provider service uses the databases specifics like Tags in InfluxDB to assign thingId, policy and |
| path information in order to get the stored data into the right scopes and to be able to retrieve the correct sets of data.</p> |
| |
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