Event streaming and event driven microservices are gaining more attention for architecting scalable cloud software and data systems. Event driven microservices communicate asynchronously over distributed event bus (also called distributed event broker). In event driven microservice architectures a producer microservice creates an event and pushes it into a distributed event broker. On the other side, a consumer microservice pulls the event out of the broker and performs the required business logic on the event. In this work, we propose a methodology and framework for tail latency (high percentile latency) SLA guarantee of event driven consumer microservices. We show a cost-efficient proactive and reactive horizontal autoscale mechanism of consumer microservices to optimize for tail latency of event processing time. In the proposed framework, each latency-sensitive consumer microservice is configured with a maximum latency for event processing, and the framework guarantees autonomous scale in and out of consumer microservice instances to target the required latency SLA under minimal number of replicas. Moreover, we show and discuss the effect of consumer microservices provisioning and synchronization time on the overall latency SLA guarantee.