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		<title>From CRUD to Event Sourcing</title>

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<section>

    <h2>From CRUD to Event Sourcing</h2>

    <p style="font-style: italic;">Why CRUD is the wrong approach for microservices</p>

    <p style="margin-top: 100px; font-weight: bold;">James Roper</p>

    <p><tt>@jroper</tt></p>

    <img style="width: 30%; margin-top: 50px; border: none; background: none; box-shadow: none;" src="assets/lightbend-logo.svg"/>
</section>

<section>
    <h2>Agenda</h2>

    <ul>
        <li class="fragment">Failure test CRUD solutions</li>
        <li class="fragment">Learn about Event Sourcing</li>
        <li class="fragment">See why Event Sourcing is resilient</li>
        <li class="fragment">Live coding!</li>
    </ul>
</section>

<section>
<section>
    <h2>Holiday Rentals</h2>

    <ul>
        <li class="fragment">Airbnb like application</li>
        <li class="fragment">Asynchronous microservice architecture</li>
        <li class="fragment">Kafka for messaging</li>
        <li class="fragment">Reservation service uses CRUD persistence</li>
    </ul>
</section>

<section>
    <h2>Architecture</h2>
    
    <img src="assets/architecture.png" />
</section>
</section>

<section>
<section>
    <h2>Service implementation</h2>

    <ul>
        <li class="fragment">Basic approach:
            <ul>
                <li class="fragment">Update database</li>
                <li class="fragment and-link"><em>and</em></li>
                <li class="fragment">Publish to Kafka</li>
            </ul>
        </li>
    </ul>
</section>    

<section>
    <h2>Naive approach</h2>
    <div class="image-fragments">
        <img src="assets/publish-after-1.png" class="fragment"/>
        <img src="assets/publish-after-2.png" class="fragment"/>
        <img src="assets/publish-after-3.png" class="fragment"/>
        <img src="assets/publish-after-4.png" class="fragment"/>
        <img src="assets/publish-after-0.png" />
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</section>

<section>
    <h2>What if something goes wrong?</h2>

    <ul>
        <li class="fragment">Is this approach resilent?</li>
        <li class="fragment">What if:
            <ul>
                <li class="fragment">The service goes down?</li>
                <li class="fragment">The database goes down?</li>
                <li class="fragment">Kafka goes down?</li>
                <li class="fragment">The network goes down?</li>
            </ul>
        </li>
    </ul>
</section>

<section>
    <h2>Naive approach</h2>
    <div class="image-fragments">
        <img src="assets/publish-after-5.png" class="fragment"/>
        <img src="assets/publish-after-6.png" class="fragment"/>
        <img src="assets/publish-after-4.png" />
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<section>
    <img src="assets/dino-rent.png" />
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</section>

<section>
<section>
    <h2>Another solution?</h2>

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        <img src="assets/commit-after-1.png" class="fragment"/>
        <img src="assets/commit-after-2.png" class="fragment"/>
        <img src="assets/commit-after-3.png" class="fragment"/>
        <img src="assets/commit-after-4.png" class="fragment"/>
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        <img src="assets/commit-after-6.png" class="fragment"/>
        <img src="assets/commit-after-0.png" />
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</section>

<section>
    <h2>Two generals problem</h2>

    <img src="assets/2-generals.png" />
</section>

<section>
    <h2>Two generals problem</h2>

    <ul>
        <li class="fragment">It is proven to be unsolveable</li>
    </ul>
</section>

<section>
    <h2>Two-phase commit</h2>

    <ul>
        <li class="fragment">Can't we just use two-phase commit?
            <ul>
                <li class="fragment">No.</li>
                <li class="fragment">Only reduces the window for failure to cause a problem</li>
                <li class="fragment">The window is largest when failure is most likely</li>
                <li class="fragment">Coordination comes at high cost</li>
            </ul>
        </li>
    </ul>
</section>
</section>

<section>
<section>
    <h2>Too hard?</h2>

    <ul>
        <li class="fragment">Maybe it's all too hard</li>
        <li class="fragment">Is inconsistency really that bad?</li>
    </ul>
</section>

<section>
    <h2>An easier way?</h2>

    <ul>
        <li class="fragment">We can't solve the 2 generals problem</li>
        <li class="fragment">What if come up with a different plan of attack?</li>
    </ul>
</section>
</section>

<section>
<section>
    <h2>Event sourcing</h2>

    <ul>
        <li class="fragment">Don't store the current state</li>
        <li class="fragment">Store the events that occurred</li>
        <li class="fragment">Compute the state from the events</li>
    </ul>
</section>

<section>
    <h2>Event sourcing</h2>

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        <img src="assets/es-append-3.png" class="fragment"/>
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        <img src="assets/es-append-5.png" class="fragment"/>
        <img src="assets/es-append-0.png"/>
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</section>

<section>
    <h2>Event sourcing</h2>

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        <img src="assets/es-publish-2.png" class="fragment"/>
        <img src="assets/es-publish-3.png" class="fragment"/>
        <img src="assets/es-publish-4.png" class="fragment"/>
        <img src="assets/es-publish-5.png" class="fragment"/>
        <img src="assets/es-publish-0.png"/>
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</section>

<section>
    <h2>Event sourcing</h2>

    <ul>
        <li>Advantages:
            <ul>
                <li class="fragment">Fact centric approach</li>
                <li class="fragment">Self healing when problems occur</li>
                <li class="fragment">Built in audit log</li>
                <li class="fragment">Compute the state of the system at any time</li>
            </ul>
        </li>
    </ul>
</section>

<section>
    <h2>Event sourcing</h2>

    <ul>
        <li>Details:
            <ul>
                <li class="fragment">How is consistency addressed?</li>
                <li class="fragment">Is replaying events expensive?</li>
                <li class="fragment">How to query data?</li>
            </ul>
        </li>
    </ul>
</section>
</section>

<section>
<section>
    <h2>Summary</h2>
    
    <ul>
        <li class="fragment">CRUD is not an ideal fit for distributed systems</li>
        <li class="fragment">Event sourcing is an ideal fit for distributed systems</li>
        <li class="fragment">Event sourcing brings a host of other advantages</li>
    </ul>
</section>

<section>
    <h2>Next steps</h2>

    <p><a href="http://lagomframework.com">https://www.lagomframework.com</a></p>
    <p><a href="https://github.com/jroper/crud-to-es">https://github.com/jroper/crud-to-es</a></p>
</section>
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