Recent trends towards microservice architectures and containers as a deployment unit raise the need for novel adaptation processes to enable elasticity for containerized microservices. Microservices facing unpredictable workloads need to react fast and match the supply as closely as possible to the demand in order to guarantee quality objectives and to keep costs at a minimum. Current state-of-the-art approaches, that react on conditions which reflect the need to scale, are either slow or lack precision in supplying the demand with the adequate capacity. Therefore, we propose a novel heuristic adaptation process which enables elasticity for a particular containerized microservice. The proposed method consists of two mechanisms that complement each other. One part reacts to changes in load intensity by scaling container instances depending on their processing capability. The other mechanism manages additional containers as a buffer to handle unpredictable workload changes. We evaluate the proposed adaptation process and discuss its effectiveness and feasibility in controlling autonomously the number of replicated containers.