What are microservices?

pattern

The beginnings of a pattern language for microservices architectures

.

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Which architecture should you choose for

an application?

• Monolithic

architecture: Design an application as a single deployable unit

• Microservices architecture: Design an application as a collection of loosely coupled

services

How to decompose an application into services?

Decompose by business capability: define services corresponding to business capabilities

• Decompose by subdomain: define services corresponding to DDD subdomains

Autonomous service: Design services to

• handle synchronous requests without waiting for other services to respondnew Team Servicenew

• Strangler app
• Anti-corruption layer

How to maintain data consistency and implement queries?

• Per-service database: Each service has its own

private database Shared database: Services share a

• database
• Saga: Use sagas, which are local transaction sequences, to maintain data consistency

across services. API composition: Implement queries by

• invoking the services that own the data and performing an in-memory join
• CQRS: Implement queries by maintaining one or more materialized views that can be efficiently queried

Domain event:

• publishes an event each time

the data changes Event source

• : persists aggregates

as a sequence of events Transactional messaging How

publish messages as part of a database transaction

?

• Transactional outbox
• Transaction log Poll

editor

How to facilitate testing?

Consumer-directed contract testing: a set of tests for a service written by the developers of another service that consumes it Consumer-side contract test: a set of tests for a service customer

• (for example, another service) that verifies that it can communicate with the

service SEST Service Component – a set of tests

• that tests a service in isolation using test doubles for any service it invokes

How to implement the services of an application?

Multiple service instances per host:

Deploy multiple service instances on a single host Service instance per host: Deploy each service instance on its own host Service instance per virtual machine: Deploy each service instance on your VM

• Per-container service instance: Deploy each service instance in your container

Serverless deployment

• :
• Deploy
• a service using the platform
• Serverless deployment Service deployment platform: Deploy services using a highly automated deployment platform that provides a service abstraction

How to handle

cross-cutting concerns?

• Microservices chassis: A framework that handles cross-cutting concerns and simplifies service development
• Outsourced configuration: Outsource all configuration, such as database location and
• credentials. Service Template: A template that implements standard cross-cutting issues and is intended to be copied by a developer to quickly start developing a new service

. Style

What communication mechanisms do services use to communicate with each other and with their external clients?

• Remote procedure invocation: Use an RPI-based

protocol for communication between services

• Messaging: Use asynchronous messaging for communication
• between services Domain-specific protocol: Use a domain-specific protocol
• Idempotent consumer: Ensure that message consumers can cope with being invoked multiple times with the same

external API

message

How do external clients communicate with

services? API Gateway: A service

• that provides

each client with a unified interface to services

• Back-end to front-end: A separate API gateway for each type of

client

Service discovery

How does the client of an RPI-based service discover the network location of a service instance?

Client-side discovery: The client queries a service log to discover the locations of the service instances Server-side discovery: The router queries a service log to discover the locations of the service instances Service logging: A database of service instance locations Automatic logging: The service instance is registered with the service log 3rd party log: a

• third party registers a service instance with
• the service log

Reliability

How to prevent a

network or service failure from cascading to other

services?

• Circuit breaker – invoke a remote service through a proxy that fails immediately when the error rate of the remote call exceeds a threshold

How to communicate the identity of the applicant to the services that handle the request?

• Access token: a token that securely stores information about the user that is exchanged between services

How to

understand the behavior of an application and troubleshoot problems?

• Log aggregation: adding application logs
• Application metrics: Instrumenting a service’s code to collect statistics about operations
• Audit logging: Logging user activity in a database

• Distributed tracing: Instrument services with code that assigns each external request a unique identifier that is passed between services. Record information (e.g., start time, end time) about work (e.g., service requests) performed when handling the external request in

a centralized service Exception tracking: Report all exceptions to a centralized exception tracking service that

• aggregates and tracks exceptions and notifies developers.

Health Check API

• : Service API (for example, HTTP endpoint) that returns the status of the service and is intended to receive ping, For example, by using a monitoring service

• Log deployments and changes

How to implement a screen or UI page that displays data from multiple services?

Server-side page snippet composition: Create a web page on the server by composing HTML snippets

generated by multiple enterprise-capacity/subdomain-specific web applications Client-side UI composition

• : Create a client-side UI by composing UI snippets

• represented by various capability-specific UI components Enterprise/Subdomain