The document discusses Toast's adoption and use of Apache Pulsar for asynchronous messaging in their microservices architecture. It describes how they built a "Pulsar Toggle" leveraging Envoy proxy to enable blue/green deployments of Pulsar consumers. The Pulsar Toggle allows consumers to be paused and resumed based on their status in the Envoy control plane, improving the reliability and usability of deploying changes to Pulsar-based services. Toast has seen increased adoption of Pulsar and benefits from its stability and scalability.