Microservices are small, autonomous services that work together to solve business problems. NATS is a messaging system that supports inter-service communication for microservices through a simple publish-subscribe model. NATS provides high performance, lightweight messaging that is easy to use. It supports building scalable, robust applications. The document discusses using NATS to implement an outpatient department application with multiple microservices that communicate through messages. Observability is implemented through logging, metrics collection and dashboards. Microservices can integrate with other enterprise systems through an integration platform.

1. Designing Microservices with
NATS
October 8, 2021

2. Microservices

3. The term microservices architecture refers
to a distributed computing architecture that is
built using a set of small, autonomous
services that act as a cohesive unit to solve a
business problem or problems

4. Advantages of Microservices
● Build highly scalable applications
● Build robust applications that withstand failures
● Better utilization of computing infrastructure
● Helps innovation with reduced time to market
● Build modular systems that are easy to manage and maintain

5. Characteristics of Microservices
● Independently deployable
● Design for failure
● Decentralized data management
● Domain driven design (finite scope per service)
● Agile development
● Container based deployments

6. Challenges of Microservices
● Inter-service communication
● Observability
● Error handling and troubleshooting
● Security

7. Inter-service communication for microservices
● Service Mesh based approach
○ Point to point communication
○ Become complex with the increase of microservices
○ Separate data plane and control plane
● Message Broker based approach
○ Fully decoupled communication
○ Complexity does not increase with the number of microservices
○ Subject based messaging

8. NATS

9. NATS:
Modern messaging framework that
allows developers and operators to
build distributed systems

10. Why NATS?
● High performance:
○ NATS performs better than most of the existing message broker products, including
Kafka and RabbitMQ.
● Lightweight:
○ It does not need sophisticated hardware and complex deployment models to support
large message volumes.
● Simple to use:
○ It supplies a simple API to use the system. NATS has clients for over 30 programming
languages.
● At most once and at least once delivery:
○ Supports message guarantees required by applications.
● Support for event handling:
○ It can handle event streams with better performance.

11. NATS use cases
● Microservice-based applications:
○ Service mesh and inter-service messaging
● Event streaming applications:
○ Observability/analytics
○ Machine learning
○ Artificial intelligence
● Command and control-based systems:
○ Internet of Things (IoT) and edge computing
○ Telemetry/sensor data/command and control
● Augmenting or replacing legacy messaging systems

12. How NATS work?
● NATS uses a subject based messaging model with a fully decoupled publisher and a
subscriber
● Supports following message distribution mechanisms
○ Publish-Subscribe (topic based)
○ Request-Reply
○ Queue groups (load balancing)
● Messages are published on a subject and the consumers subscribe to the subject
● Wildcard subscriptions are allowed so that consumers can listen to messages from different
subjects and different publishers

13. NATS subject based messaging
● Supports wiretap messaging with
wildcard “>”
● Multi character wildcard can be
used to listen on a certain pattern of
subjects
● Specific subject name is used to
receive messages from specific
publishers

14. NATS request-reply messaging
● Publisher specifies a reply subject
(inbox)
● Subscriber respond through the
reply subject
● NATS can filter multiple responses
and send the first (fastest) response

15. NATS queue-groups messaging
● Publisher publishes on a subject. It
is not aware of the queue group
● Subscribers form a queue group by
specifying a common name for the
queue parameter
● Messages are delivered to the
subscribers in a load balanced
manner

16. NATS Clustering
● Helps scaling the NATS infrastructure according to the requirements of the application
● Clustering forms a fully connected server mesh. All nodes are aware of all the other nodes.
● Nodes are connected via sending simple messages (gossip) and does not require
pre-configuration of all the nodes
● Messages are replicated to one of the adjacent node so that node failure does not cause a
message loss
● Publisher and Subscriber can connect to different nodes (location transparency) to share
messages
● Most applications can be supported with a 3-node cluster

17. Microservices with NATS

18. Microservices Inner-Outer Architecture
● Microservices does not exist in isolation.
● Inner Architecture deals with
○ Individual microservices
○ Inter-Service Communication
● Outer Architecture deals with
○ Integration with other parts of the enterprise platform
○ Governance of the microservices teams and processes
○ Shared services such as automation, infrastructure, observability

19. Microservices Inner-Outer Architecture

20. Building an Outpatient Department (OPD) Application
● A hospital OPD unit performs various tasks related to patient care
● Patient Registration
○ Admit new patients to the unit and register them on the system
● Patient Inspection
○ A physician inspect the patient and decide on the next steps
● Patient Treatment
○ Based on the inspection, nurses take care of the temporary treatments including
medication and doing various tests
● Patient Release
○ Once the temporary treatment is done, patient is discharged from the unit and send
back home or admit to a long term ward for further treatments

21. OPD Application Design with NATS

22. OPD Application Implementation
● Each microservice has its own database to store data related to that microservice
● Messages are used to share data between services
● Registration Service stores the patient details in the database and publish an event to the
inspection service with the patient ID and token number
● Inspection Service listens to the event and do the inspection and update its database with
inspection details. The required information is passed to the treatment service via an event.
● Treatment service receives the event and take actions accordingly and store the medication
schedules and test results in its database. Once the patient is ready to be released, it sends a
message via an event to the release service.
● Release service receives the event and discharge the patient and update its database.

23. Securing Microservices
● Security for external communications
○ Client applications consuming the services
○ Different types of clients including mobile, web and
standalone
○ Require advanced, standard security
○ OAuth 2.0 is becoming the de facto
○ API Gateways provides a standard mechanism to
implement security
● Security for internal communications
○ Services communicate with the NATS server
○ NATS support basic authentication, key based
authentication, JWT based authentication
○ Security can be implemented with TLS only since
consumers are internal (trusted subsystem)

24. Observability for Microservices with NATS
● Observability is a characteristic of the platform which defines how well the internal states of
a platform can be inferred from the knowledge of its external output
● It is a responsibility of each component in the platform to implement enough observability
through the external output such as
○ Log entries
○ Health check endpoints
○ Metrics endpoints
○ Application dashboards
● NATS supports observability through
○ Logging
○ Monitoring endpoints

25. Implementing Observability for Microservices with NATS

26. Implementing Observability for Microservices with NATS
● Microservices implements /healthz and /metrics endpoints to provide application statistics
and status.
● Microservices publish logs to application specific log files
● NATS server has a separate log file and a set of endpoints to collect application statistics
● Prometheus collects application statistics from the endpoints of microservices and the NATS
server and publishes to Grafana
● Promtail and Loki collects log entries and publishes to Grafana for visualization
● Grafana is used to create dashboards for microservices and NATS server monitoring and
alert generation

27. Microservices and Integration Platforms
● Enterprise platforms consists of heterogeneous systems that needs to be integrated.
● Microservices based applications are one such component in the overall architecture.
● Integration Platforms plays a pivotal role in enterprise by doing
○ Application Integration
○ Data Integration
○ B2B Integration
○ API Management
● Microservices needs to co-exist with Integration Platforms

28. Microservices and Integration Platforms

29. Microservices and Integration Platforms
● API-driven architecture is common within enterprise software platforms
● Services implemented at different layers based on their functionality and exposes APIs so
that subsequent layers can consume
● Microservices can implement services at one of these layers or at core business functionality
layer
● Microservices can integrate with other parts of the enterprise platform through the
integration platform since it supports the interoperability and acts as the anti-corruption
layer

30. Future of Microservices and NATS
● Trends/Developments in Microservices domain
○ Service Mesh is becoming popular though most people still failing to use it
○ Usage of Saga pattern to implement transactional microservices
○ Serverless platforms provides easier approach to build microservices based applications
● What’s new in NATS?
○ JetStream is becoming popular for streaming use cases of NATS which requires
advanced message delivery guarantees and persistence
○ NATS is used to build asynchronous logging frameworks and Service Mesh

31. Future of Microservices and NATS
● Trends/Developments in Microservices domain
○ Service Mesh is becoming popular though most people still failing to use it
○ Usage of Saga pattern to implement transactional microservices
○ Serverless platforms provides easier approach to build microservices based applications
● What’s new in NATS?
○ JetStream is becoming popular for streaming use cases of NATS which requires
advanced message delivery guarantees and persistence
○ NATS is used to build asynchronous logging frameworks and Service Mesh

32. Learn More
● The book that contains more
details can be found here
https://www.packtpub.com/product/d
esigning-microservices-platforms-wit
h-nats/9781801072212

33. Follow me
Chanaka Fernando, Associate
Director @ WSO2
Medium - https://medium.com/@chanakaudaya
Twitter - https://twitter.com/chanakaudaya
LinkedIn - https://www.linkedin.com/in/chanakaudaya
Github - https://github.com/chanakaudaya