This talk will cover the journey and findings of firefighting a complex Symfony application (with Messenger, Serializer, Varnish, Redis, RabbitMQ, and Elasticsearch) with Blackfire.

The topics covered will be:
- Bottleneck within the Serializer
- Caching serialized object
- Digging into Elasticsearch APIs and some internals

To finally find the root cause of a spike of http-500 errors in a public facing API with 2M requests.

All of that by using the Blackfire profiling features.