Spring Cloud - Bootstrapping

1. Gambaran keseluruhan

Spring Cloud adalah rangka kerja untuk membina aplikasi cloud yang mantap. Kerangka kerja ini memudahkan pengembangan aplikasi dengan memberikan solusi untuk banyak masalah umum yang dihadapi ketika berpindah ke lingkungan yang diedarkan.

Aplikasi yang dijalankan dengan seni bina perkhidmatan mikro bertujuan untuk mempermudah pembangunan, penggunaan, dan pemeliharaan. Sifat aplikasi yang terurai membolehkan pembangun memberi tumpuan kepada satu masalah pada satu masa. Penambahbaikan dapat diperkenalkan tanpa mempengaruhi bahagian sistem yang lain.

Sebaliknya, pelbagai cabaran muncul ketika kita menggunakan pendekatan perkhidmatan mikro:

  • Melengkapkan konfigurasi sehingga fleksibel dan tidak memerlukan penyusunan semula perkhidmatan semasa perubahan
  • Penemuan perkhidmatan
  • Menyembunyikan kerumitan perkhidmatan yang digunakan pada host yang berbeza

Dalam artikel ini, kami akan membina lima perkhidmatan mikro: pelayan konfigurasi, pelayan penemuan, pelayan gerbang, perkhidmatan buku, dan akhirnya perkhidmatan penarafan. Lima perkhidmatan mikro ini membentuk aplikasi asas yang kukuh untuk memulakan pengembangan awan dan menangani cabaran yang disebutkan di atas.

2. Konfigurasi Pelayan

Semasa mengembangkan aplikasi cloud, satu masalah adalah menjaga dan menyebarkan konfigurasi ke perkhidmatan kami. Kami sebenarnya tidak mahu meluangkan masa untuk mengkonfigurasi setiap persekitaran sebelum menskalakan perkhidmatan kami secara mendatar atau berisiko melanggar keselamatan dengan memasukkan konfigurasi ke dalam aplikasi kami.

Untuk menyelesaikannya, kami akan menggabungkan semua konfigurasi kami ke dalam satu repositori Git dan menghubungkannya ke satu aplikasi yang menguruskan konfigurasi untuk semua aplikasi kami. Kami akan membuat pelaksanaan yang sangat sederhana.

Untuk mengetahui lebih terperinci dan melihat contoh yang lebih kompleks, lihat artikel Spring Cloud Configuration kami.

2.1. Persediaan

Navigasi ke //start.spring.io dan pilih Maven and Spring Boot 2.2.x.

Tetapkan artifak ke "config " . Di bahagian kebergantungan, cari "config server" dan tambahkan modul itu. Kemudian tekan butang menjana dan kami akan dapat memuat turun fail zip dengan projek yang telah dikonfigurasikan di dalamnya dan siap untuk digunakan.

Sebagai alternatif, kita boleh menghasilkan projek Spring Boot dan menambahkan beberapa kebergantungan pada fail POM secara manual.

Pergantungan ini akan dikongsi antara semua projek:

 org.springframework.boot spring-boot-starter-parent 2.2.6.RELEASE     org.springframework.boot spring-boot-starter-test test      org.springframework.cloud spring-cloud-dependencies Hoxton.SR4 pom import       org.springframework.boot spring-boot-maven-plugin   

Mari tambahkan kebergantungan untuk pelayan konfigurasi:

 org.springframework.cloud spring-cloud-config-server 

Sebagai rujukan, kita dapat mencari versi terbaru di Maven Central ( spring-cloud-dependencies, test, config-server ).

2.2. Spring Config

Untuk mengaktifkan pelayan konfigurasi, kita mesti menambahkan beberapa anotasi ke kelas aplikasi utama:

@SpringBootApplication @EnableConfigServer public class ConfigApplication {...}

@EnableConfigServer akan mengubah aplikasi kami menjadi pelayan konfigurasi.

2.3. Hartanah

Mari tambahkan application.properties dalam src / main / sumber :

server.port=8081 spring.application.name=config spring.cloud.config.server.git.uri=file://${user.home}/application-config

Tetapan yang paling ketara untuk pelayan konfigurasi adalah parameter git.uri . Ini sekarang ditetapkan ke jalur fail relatif yang secara amnya dapat diselesaikan ke c: \ Users \ {username} \ pada Windows atau / Users / {username} / on * nix. Properti ini menunjuk ke repositori Git di mana fail harta tanah untuk semua aplikasi lain disimpan. Ia boleh ditetapkan ke jalur fail mutlak jika perlu.

Petua : Pada mesin windows, awalkan nilainya dengan "file: ///", pada * nix kemudian gunakan "file: //".

2.4. Git Repositori

Navigasi ke folder yang ditentukan oleh spring.cloud.config.server.git.uri dan tambahkan folder application-config . CD ke dalam folder itu dan taip git init . Ini akan memulakan repositori Git di mana kita dapat menyimpan fail dan mengesan perubahannya.

2.5. Lari

Mari jalankan pelayan konfigurasi dan pastikan ia berfungsi. Dari baris arahan jenis mvn spring-boot: run . Ini akan memulakan pelayan.

Kita harus melihat output ini menunjukkan pelayan sedang berjalan:

Tomcat started on port(s): 8081 (http)

2.6. Konfigurasi Bootstrapping

Di pelayan berikutnya, kami ingin harta aplikasi mereka dikendalikan oleh pelayan konfigurasi ini. Untuk melakukan itu, kita sebenarnya perlu melakukan sedikit ayam dan telur: Konfigurasikan sifat di setiap aplikasi yang tahu bagaimana bercakap dengan pelayan ini.

Ini adalah proses bootstrap, dan setiap aplikasi ini akan mempunyai fail bernama bootstrap.properties . Ia akan mengandungi sifat seperti application.properties tetapi dengan kelainan:

Spring ApplicationContext ibu bapa memuatkan bootstrap.properties terlebih dahulu. Ini sangat penting sehingga Config Server dapat mula menguruskan hartanah di application.properties . ApplicationContext khas ini juga akan menyahsulitkan sebarang sifat aplikasi yang dienkripsi.

Adalah bijak untuk membezakan fail sifat ini. bootstrap.properties adalah untuk menyiapkan pelayan konfigurasi, dan application.properties adalah untuk sifat khusus untuk aplikasi kami. Namun, secara teknikal, mungkin meletakkan sifat aplikasi di bootstrap.properties .

Terakhir, kerana Config Server menguruskan harta aplikasi kami, seseorang mungkin bertanya-tanya mengapa mempunyai aplikasi.properties sama sekali? Jawapannya adalah bahawa ini masih berguna sebagai nilai lalai yang mungkin tidak dimiliki oleh Config Server.

3. Penemuan

Now that we have configuration taken care of, we need a way for all of our servers to be able to find each other. We will solve this problem by setting the Eureka discovery server up. Since our applications could be running on any ip/port combination we need a central address registry that can serve as an application address lookup.

When a new server is provisioned it will communicate with the discovery server and register its address so that others can communicate with it. This way other applications can consume this information as they make requests.

To learn more details and see a more complex discovery implementation take a look at Spring Cloud Eureka article.

3.1. Setup

Again we'll navigate to start.spring.io. Set the artifact to “discovery”. Search for “eureka server” and add that dependency. Search for “config client” and add that dependency. Finally, generate the project.

Alternatively, we can create a Spring Boot project, copy the contents of the POM from config server and swap in these dependencies:

 org.springframework.cloud spring-cloud-starter-config   org.springframework.cloud spring-cloud-starter-eureka-server 

For reference, we'll find the bundles on Maven Central (config-client, eureka-server).

3.2. Spring Config

Let's add Java config to the main class:

@SpringBootApplication @EnableEurekaServer public class DiscoveryApplication {...}

@EnableEurekaServer will configure this server as a discovery server using Netflix Eureka. Spring Boot will automatically detect the configuration dependency on the classpath and lookup the configuration from the config server.

3.3. Properties

Now we will add two properties files:

First, we add bootstrap.properties into src/main/resources:

spring.cloud.config.name=discovery spring.cloud.config.uri=//localhost:8081

These properties will let discovery server query the config server at startup.

And second, we add discovery.properties to our Git repository

spring.application.name=discovery server.port=8082 eureka.instance.hostname=localhost eureka.client.serviceUrl.defaultZone=//localhost:8082/eureka/ eureka.client.register-with-eureka=false eureka.client.fetch-registry=false

The filename must match the spring.application.name property.

In addition, we are telling this server that it is operating in the default zone, this matches the config client's region setting. We are also telling the server not to register with another discovery instance.

In production, we'd have more than one of these to provide redundancy in the event of failure and that setting would be true.

Let's commit the file to the Git repository. Otherwise, the file will not be detected.

3.4. Add Dependency to the Config Server

Add this dependency to the config server POM file:

 org.springframework.cloud spring-cloud-starter-eureka 

For reference, we can find the bundle on Maven Central (eureka-client).

Add these properties to the application.properties file in src/main/resources of the config server:

eureka.client.region = default eureka.client.registryFetchIntervalSeconds = 5 eureka.client.serviceUrl.defaultZone=//localhost:8082/eureka/

3.5. Run

Start the discovery server using the same command, mvn spring-boot:run. The output from the command line should include:

Fetching config from server at: //localhost:8081 ... Tomcat started on port(s): 8082 (http)

Stop and rerun the config service. If all is good output should look like:

DiscoveryClient_CONFIG/10.1.10.235:config:8081: registering service... Tomcat started on port(s): 8081 (http) DiscoveryClient_CONFIG/10.1.10.235:config:8081 - registration status: 204

4. Gateway

Now that we have our configuration and discovery issues resolved we still have a problem with clients accessing all of our applications.

If we leave everything in a distributed system, then we will have to manage complex CORS headers to allow cross-origin requests on clients. We can resolve this by creating a gateway server. This will act as a reverse proxy shuttling requests from clients to our back end servers.

A gateway server is an excellent application in microservice architecture as it allows all responses to originate from a single host. This will eliminate the need for CORS and give us a convenient place to handle common problems like authentication.

4.1. Setup

By now we know the drill. Navigate to //start.spring.io. Set the artifact to “gateway”. Search for “zuul” and add that dependency. Search for “config client” and add that dependency. Search for “eureka discovery” and add that dependency. Lastly, generate that project.

Alternatively, we could create a Spring Boot app with these dependencies:

 org.springframework.cloud spring-cloud-starter-config   org.springframework.cloud spring-cloud-starter-eureka   org.springframework.cloud spring-cloud-starter-zuul 

For reference, we can find the bundle on Maven Central (config-client, eureka-client, zuul).

4.2. Spring Config

Let's add the configuration to the main class:

@SpringBootApplication @EnableZuulProxy @EnableEurekaClient public class GatewayApplication {...}

4.3. Properties

Now we will add two properties files:

bootstrap.properties in src/main/resources:

spring.cloud.config.name=gateway spring.cloud.config.discovery.service-id=config spring.cloud.config.discovery.enabled=true eureka.client.serviceUrl.defaultZone=//localhost:8082/eureka/

gateway.properties in our Git repository

spring.application.name=gateway server.port=8080 eureka.client.region = default eureka.client.registryFetchIntervalSeconds = 5 zuul.routes.book-service.path=/book-service/** zuul.routes.book-service.sensitive-headers=Set-Cookie,Authorization hystrix.command.book-service.execution.isolation.thread.timeoutInMilliseconds=600000 zuul.routes.rating-service.path=/rating-service/** zuul.routes.rating-service.sensitive-headers=Set-Cookie,Authorization hystrix.command.rating-service.execution.isolation.thread.timeoutInMilliseconds=600000 zuul.routes.discovery.path=/discovery/** zuul.routes.discovery.sensitive-headers=Set-Cookie,Authorization zuul.routes.discovery.url=//localhost:8082 hystrix.command.discovery.execution.isolation.thread.timeoutInMilliseconds=600000

The zuul.routes property allows us to define an application to route certain requests based on an ant URL matcher. Our property tells Zuul to route any request that comes in on /book-service/** to an application with the spring.application.name of book-service. Zuul will then lookup the host from discovery server using the application name and forward the request to that server.

Remember to commit the changes in the repository!

4.4. Run

Run the config and discovery applications and wait until the config application has registered with the discovery server. If they are already running, we don't have to restart them. Once that is complete, run the gateway server. The gateway server should start on port 8080 and register itself with the discovery server. The output from the console should contain:

Fetching config from server at: //10.1.10.235:8081/ ... DiscoveryClient_GATEWAY/10.1.10.235:gateway:8080: registering service... DiscoveryClient_GATEWAY/10.1.10.235:gateway:8080 - registration status: 204 Tomcat started on port(s): 8080 (http)

One mistake that is easy to make is to start the server before config server has registered with Eureka. In this case, we'll see a log with this output:

Fetching config from server at: //localhost:8888

This is the default URL and port for a config server and indicates our discovery service did not have an address when the configuration request was made. Just wait a few seconds and try again, once the config server has registered with Eureka, the problem will resolve.

5. Book Service

In microservice architecture, we are free to make as many applications to meet a business objective. Often engineers will divide their services by domain. We will follow this pattern and create a book service to handle all the operations for books in our application.

5.1. Setup

One more time. Navigate to //start.spring.io. Set the artifact to “book-service”. Search for “web” and add that dependency. Search for “config client” and add that dependency. Search for “eureka discovery” and add that dependency. Generate that project.

Alternatively, add these dependencies to a project:

 org.springframework.cloud spring-cloud-starter-config   org.springframework.cloud spring-cloud-starter-eureka   org.springframework.boot spring-boot-starter-web 

For reference, we can find the bundle on Maven Central (config-client, eureka-client, web).

5.2. Spring Config

Let's modify our main class:

@SpringBootApplication @EnableEurekaClient @RestController @RequestMapping("/books") public class BookServiceApplication { public static void main(String[] args) { SpringApplication.run(BookServiceApplication.class, args); } private List bookList = Arrays.asList( new Book(1L, "Baeldung goes to the market", "Tim Schimandle"), new Book(2L, "Baeldung goes to the park", "Slavisa") ); @GetMapping("") public List findAllBooks() { return bookList; } @GetMapping("/{bookId}") public Book findBook(@PathVariable Long bookId) { return bookList.stream().filter(b -> b.getId().equals(bookId)).findFirst().orElse(null); } }

We also added a REST controller and a field set by our properties file to return a value we will set during configuration.

Let's now add the book POJO:

public class Book { private Long id; private String author; private String title; // standard getters and setters }

5.3. Properties

Now we just need to add our two properties files:

bootstrap.properties in src/main/resources:

spring.cloud.config.name=book-service spring.cloud.config.discovery.service-id=config spring.cloud.config.discovery.enabled=true eureka.client.serviceUrl.defaultZone=//localhost:8082/eureka/

book-service.properties in our Git repository:

spring.application.name=book-service server.port=8083 eureka.client.region = default eureka.client.registryFetchIntervalSeconds = 5 eureka.client.serviceUrl.defaultZone=//localhost:8082/eureka/

Let's commit the changes to the repository.

5.4. Run

Once all the other applications have started we can start the book service. The console output should look like:

DiscoveryClient_BOOK-SERVICE/10.1.10.235:book-service:8083: registering service... DiscoveryClient_BOOK-SERVICE/10.1.10.235:book-service:8083 - registration status: 204 Tomcat started on port(s): 8083 (http)

Once it is up we can use our browser to access the endpoint we just created. Navigate to //localhost:8080/book-service/books and we get back a JSON object with two books we added in out controller. Notice that we are not accessing book service directly on port 8083 but we are going through the gateway server.

6. Rating Service

Like our book service, our rating service will be a domain driven service that will handle operations related to ratings.

6.1. Setup

One more time. Navigate to //start.spring.io. Set the artifact to “rating-service”. Search for “web” and add that dependency. Search for “config client” and add that dependency. Search for eureka discovery and add that dependency. Then, generate that project.

Alternatively, add these dependencies to a project:

 org.springframework.cloud spring-cloud-starter-config   org.springframework.cloud spring-cloud-starter-eureka   org.springframework.boot spring-boot-starter-web 

For reference, we can find the bundle on Maven Central (config-client, eureka-client, web).

6.2. Spring Config

Let's modify our main class:

@SpringBootApplication @EnableEurekaClient @RestController @RequestMapping("/ratings") public class RatingServiceApplication { public static void main(String[] args) { SpringApplication.run(RatingServiceApplication.class, args); } private List ratingList = Arrays.asList( new Rating(1L, 1L, 2), new Rating(2L, 1L, 3), new Rating(3L, 2L, 4), new Rating(4L, 2L, 5) ); @GetMapping("") public List findRatingsByBookId(@RequestParam Long bookId)  bookId.equals(0L) ? Collections.EMPTY_LIST : ratingList.stream().filter(r -> r.getBookId().equals(bookId)).collect(Collectors.toList());  @GetMapping("/all") public List findAllRatings() { return ratingList; } }

We also added a REST controller and a field set by our properties file to return a value we will set during configuration.

Let's add the rating POJO:

public class Rating { private Long id; private Long bookId; private int stars; //standard getters and setters }

6.3. Properties

Now we just need to add our two properties files:

bootstrap.properties in src/main/resources:

spring.cloud.config.name=rating-service spring.cloud.config.discovery.service-id=config spring.cloud.config.discovery.enabled=true eureka.client.serviceUrl.defaultZone=//localhost:8082/eureka/

rating-service.properties in our Git repository:

spring.application.name=rating-service server.port=8084 eureka.client.region = default eureka.client.registryFetchIntervalSeconds = 5 eureka.client.serviceUrl.defaultZone=//localhost:8082/eureka/

Let's commit the changes to the repository.

6.4. Run

Once all the other applications have started we can start the rating service. The console output should look like:

DiscoveryClient_RATING-SERVICE/10.1.10.235:rating-service:8083: registering service... DiscoveryClient_RATING-SERVICE/10.1.10.235:rating-service:8083 - registration status: 204 Tomcat started on port(s): 8084 (http)

Once it is up we can use our browser to access the endpoint we just created. Navigate to //localhost:8080/rating-service/ratings/all and we get back JSON containing all our ratings. Notice that we are not accessing the rating service directly on port 8084 but we are going through the gateway server.

7. Conclusion

Sekarang kita dapat menghubungkan pelbagai kepingan Spring Cloud ke dalam aplikasi perkhidmatan mikro yang berfungsi. Ini membentuk asas yang dapat kita gunakan untuk mula membangun aplikasi yang lebih kompleks.

Seperti biasa, kita dapat mencari kod sumber ini di GitHub.