Spring Cloud URL Shortener

kURLy - a microservice for URL shortening.

Description

Cloud-native is an approach to building and running applications that exploits the advantages of the cloud computing model.

Microservices is an architectural approach to developing an application as a collection of small services; each service implements business capabilities, runs in its own process and communicates via an HTTP API. Each microservice can be deployed, upgraded, scaled, and restarted independent of other services in the application, typically as part of an automated system.

(c) Pivotal

We're breaking large applications into smaller pieces called 'services'. And each of these services can be deployed and scaled on their own. How does one service locate another?

Service Discovery

Module	URL
discovery-server	http://host:8761/eureka

There're multiple ways you can discover services in Spring Cloud:

• Spring Cloud Consul
• Spring Cloud Zookeeper
• Spring Cloud Netflix

This project specifically focuses on the last one, the Spring Cloud Netflix project. The US-based giant of cloud-based streaming media services, namely Netflix, has open-sourced its framework of microservice tools.

For the sake of simplicity, there's a single instance of Eureka server. Therefore Eureka server is configured not to trying register itself with its peers. You may want to have multiple discovery servers for high availability in production, so change the following properties:

eureka.client.register-with-eureka=true
eureka.client.fetch-registry=true

High Availability

Eureka is constantly ensuring that application services that it's returning or handing back to clients are healthy and available. And it's also ensuring that in case if Discovery Server goes down all clients still continue to operate.

Eureka was built with high availability in mind:

• The registry is distributed (cached locally on every client).
• Clients can operate without discovery server (if this server goes down).
• Clients fetch deltas to update registry.

Dashboard

A web based Eureka dashboard is enabled by default. It shows useful information such as services metadata.

In local environment it's available at http://localhost:8761

Kurly Service

Module	URL
kurly-service	http://host:port/shorten

The @EnableDiscoveryClient annotation is used to turn KurlyServiceApplication into a client of the Discovery Server and it causes it to register with the Discovery Server when it starts up.

Kurly App

Module	URL
kurly-app	http://host:port/

The @EnableDiscoveryClient annotation is used to turn KurlyAppApplication into a client of the Discovery Server.

Fault Tolerance

In a Distributed System one thing is absolutely certain... FAILURE IS INEVITABLE.

A particularly bad effect of failures in a distributed system is a cascading failure. From Wikipedia:

It is a process in a system of interconnected parts in which the failure of one or few parts can trigger the failure of other parts and so on.

How to embrace failure?

• Fault tolerance
• Graceful degradation
• Constrain resources

Circuit breaker design pattern is a design pattern used in modern software development. It is used to detect failures and encapsulates the logic of preventing a failure from constantly recurring

(From Wikipedia)

Hystrix

💀 Deprecated in 2023

Netflix Hystrix is a latency and fault tolerance library designed to isolate points of access to remote systems, services and 3rd party libraries, stop cascading failure and enable resilience in complex distributed systems where failure is inevitable.

See How it works.

Hystrix Dashboard

💀 Deprecated in 2023

Module	URL
hystrix-dashboard	http://host:port/hystrix

Documentation: Circuit Breaker: Hystrix Dashboard

Turbine

💀 Deprecated in 2023

Module	URL
turbine	http://host:3000/turbine.stream

Hystrix dashboard can only monitor one microservice at a time. If there are many microservices, then the Hystrix dashboard pointing to the service has to be changed every time when switching the microservices to the monitor. It is tedious.

Turbine (provided by the Spring Cloud Netflix project), aggregates multiple instances Hystrix metrics streams, so the dashboard can display an aggregate view.

Config example:

turbine.app-config=kurly-app
turbine.cluster-name-expression='default'

Centralized configuration

Module	URL
config-server	http://host:8888/service-name/application.properties

It fetches configuration from a remote Git repository: https://github.com/naXa777/spring-cloud-url-shortener-config

After pushing new config to the repository, call http post http://service-host:port/actuator/refresh to trigger properties refresh.

Building and Running Locally

Prepare

Before the first build you need to take additional steps.

1. Clone the repository.
2. Define some environment variables.
3. 📗 TODO

You have a freedom of choosing build tools for this project: Gradle or your favourite IDE. IntelliJ IDEA, STS / Eclipse, or NetBeans should handle this task smoothly.

Using Gradle Wrapper

./gradlew :discovery-server:bootRun
./gradlew :config-server:bootRun
./gradlew :kurly-service:bootRun
./gradlew :kurly-app:bootRun
./gradlew :turbine:bootRun
./gradlew :hystrix-dashboard:bootRun

Using IntelliJ IDEA

1. Import root project in IntelliJ IDEA
2. Sync project files with Gradle (initial sync may happen automatically)
3. Now you should have multiple run configurations for every module. Run them one-by-one:
   1. DiscoveryServerApplication
   2. ConfigServerApplication
   3. KurlyServiceApplication
   4. KurlyAppApplication
   5. TurbineApplication
   6. HystrixDashboardApplication

Tip: make sure that you run them on different ports and these ports are free, otherwise you'll get an error.

Deploying to the Cloud

📗 TODO

Continuous Integration

Travis CI

License

This project is licensed under the terms of the GNU GPL v3 license.