Why every developer should parallelize serializer (#804)

March 24, 2026 at 6:43:23 AM Alice Smith

Testing in Production

Yes, you read that right. Testing in production — not instead of staging, but in addition to it. Here's why and how.

Why Staging Lies

Staging environments differ from production in subtle but critical ways:

Different data volumes (10K rows vs 10M rows)
Different traffic patterns (no real users)
Different infrastructure (smaller instances)
Different integrations (sandbox APIs)

Canary Deployments

Route a small percentage of traffic to the new version:

# nginx.conf
upstream backend {
    server app-v1:8080 weight=95;
    server app-v2:8080 weight=5;
}

Monitor error rates, latency percentiles, and business metrics. If anything degrades, roll back automatically.

Feature Flags

Decouple deployment from release:

Deploy code to 100% of servers
Enable feature for 1% of users
Gradually increase to 5%, 25%, 100%
Kill switch: disable instantly without redeployment

Observability

You can't test what you can't see. Invest in:

Structured logging (JSON, correlation IDs)
Distributed tracing (OpenTelemetry)
Custom metrics (business KPIs, not just CPU/memory)
Alerting (on symptoms, not causes)

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2 comments

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This is a demo application built in the Symfony Framework to illustrate the recommended way of developing Symfony applications.

For more information, check out the Symfony doc.

Click on this button to show the source code of the Controller and template used to render this page.

src/Controller/BlogController.php at line 272

/**
 * NOTE: when the controller argument is a Doctrine entity, Symfony makes an
 * automatic database query to fetch it based on the value of the route parameters.
 * The '{slug:post}' configuration tells Symfony to use the 'slug' route
 * parameter in the database query that fetches the entity of the $post argument.
 * This is mostly useful when the route has multiple parameters and the controller
 * also has multiple arguments.
 * See https://symfony.com/doc/current/doctrine.html#automatically-fetching-objects-entityvalueresolver.
 */
#[Route('/posts/{slug:post}', name: 'blog_post', requirements: ['slug' => Requirement::ASCII_SLUG], methods: ['GET'])]
public function postShow(Post $post): Response
{
    // Symfony's 'dump()' function is an improved version of PHP's 'var_dump()' but
    // it's not available in the 'prod' environment to prevent leaking sensitive information.
    // It can be used both in PHP files and Twig templates, but it requires to
    // have enabled the DebugBundle. Uncomment the following line to see it in action:
    //
    // dump($post, $this->getUser(), new \DateTime());
    //
    // The result will be displayed either in the Symfony Profiler or in the stream output.
    // See https://symfony.com/doc/current/profiler.html
    // See https://symfony.com/doc/current/templates.html#the-dump-twig-utilities
    //
    // You can also leverage Symfony's 'dd()' function that dumps and
    // stops the execution

    return $this->render('blog/post_show.html.twig', ['post' => $post]);
}

templates/blog/post_show.html.twig at line 1

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