Context: Several companies are migrating their information systems into the Cloud. Microservices and DevOps are two of the most common adopted technologies. However, there is still a lack of understanding how to adopt a microservice-based architectural style and which tools and technique to use in a continuous architecting pipeline. Objective: We aim at characterizing the different microservice architectural style principles and patterns in order to map existing tools and techniques adopted in the context of DevOps. Methodology: We conducted a Systematic Mapping Study identifying the goal and the research questions, the bibliographic sources, the search strings, and the selection criteria to retrieve the most relevant papers. Results: We identified several agreed microservice architectural principles and patterns widely adopted and reported in 23 case studies, together with a summary of the advantages, disadvantages, and lessons learned for each pattern from the case studies. Finally, we mapped the existing microservices-specific techniques in order to understand how to continuously deliver value in a DevOps pipeline. We depicted the current research, reporting gaps and trends. Conclusion: Different patterns emerge for different migration, orchestration, storage and deployment settings. The results also show the lack of empirical work on microservices-specific techniques, especially for the release phase in DevOps.