This Note contains:

• Microservices

• Monolithic Development
  • Downside
• Microservice
  • Key characteristics
  • Granularity of services
  • Topology
  • Front End Variety
  • Cross-cutting concerns
    • Sidecar Pattern
    • Service Mesh
  • Scalability
  • Elasticity
  • Benefit
  • Disadvantages

Monolithic Development

All components are

Downside

Reliability

Need to redeploy the entire application on each update,

Difficulty in adopting new technology

Microservice

The system is decomposed into modules not only at development time, but also at runtime.

Changes in one module are less likely to cause problems in other modules.

Key characteristics

A large application built as a suite of modular services

• Each service supports a specific business goal

• Each service uses a simple, well-defined interface to communicate with ither service

• Loosely coupled service

  • Keep services intercommunication to minimum

micro services is label and not the description. –Martin Fowler

Granularity of services

Single-purpose service that does one thing, really well.

• Single Responsibility principle: a module should ne responsible to one, and only one, actor

Can a service be managed by a small, agile team?

Avoid the entity trap: database entities mapped to services

• Example: Sandwich - recipe and ingredient as dedicated services.

Experiment to find the right granularity for your context.

Topology

Every service has all it needs to realize its business goal

• Shared database increase coupling

API Gateway acts as a service-access facade

• Clients don’t need to know service endpoints.
• Can perform various functions:
  • Authentication
  • Authorization
  • loading
  • balancing

Front End Variety

Cross-cutting concerns

A concern applicable throughout the application and it affect the entire application.

Operational concerns like monitoring and logging benefit from coupling.

Sidecar Pattern

A single-node pattern made up to containers

• application container core logic for the application
• sidecar container: augment the application container with cross-cutting concerns

Service Mesh

A dedicated infrastructure layer to control how services communicate with one another,

• Each service forms a node in the overall mesh
• The service mesh itself forms a console allowing holistic access to services.

Scalability

Simple to scale horizontally by running multiple copies.

You can target scaling only microservices that need it

Load balancing mechanism is needed:

• Distributing a set of tasks over a set of resources to make the overall processing more efficient.

Elasticity

Microservices-based applications typically run in containerized environments.

• The number of instances of a service and its locations changes dynamically

Service discovery keeps track of the addresses of all instances.

• Based on demand new instances can be created
• Can be a dedicated service or part of a service mesh

Enabler of elasticity and on-demand provisioning of resources (cloud).

Benefit

Small services foster testability and maintainability.

Services are independently deployable and scalable

• Positively impacts elasticity and resilience

Enables modern SE practices

• Automation (CI/CD, DevOps),

Disadvantages

Performance can be an issue as many network calls are needed to complete work.

Developers must implement the inter-service

• Use cases that span multiple services without using distribute