Developers are turning to microservices as a way to build scalable applications. Microservices are a type of software architecture where large applications are built as a collection of small, independent services. This approach has many benefits, including the ability to update and deploy services independently, and the ability to scale services horizontally.
While microservices offer many benefits, they can also be complex to manage. That's where Docker comes in. Docker is a containerization platform that makes it easy to package, deploy, and manage microservices.
In this article, we'll take a look at how to use Docker and Spring Boot to develop and deploy microservices. We'll start with a simple example, then we'll explore some of the more advanced features that Spring Boot and Docker offer for developing microservices.
Spring Boot is a Java-based framework that makes it easy to create stand-alone, production-grade Spring-based applications. It provides a number of features that make it easy to develop and deploy microservices, including:
Docker is a containerization platform that makes it easy to package, deploy, and manage applications. Docker containers are self-contained, isolated environments that make it easy to package and deploy applications.
Docker containers are lightweight and portable, making them ideal for microservices. They also have the added benefit of being platform agnostic, so they can be deployed on any platform that supports Docker.
In this section, we'll see how to develop and deploy a simple microservice using Spring Boot and Docker.
First, we'll need to create a new Spring Boot project. We can do this using the Spring Initializr. The Initializr is a web-based tool that makes it easy to create Spring Boot projects.
We'll start by creating a simple Maven project. We'll name our project "hello-world" and we'll use the latest version of Spring Boot (2.0.4 at the time of writing). We'll also add the "Web" and "Actuator" dependencies, as we'll need both of these for our example.
Once the project has been created, we'll need to add a few dependencies to our pom.xml
file:
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
</dependencies>
Now that we have our project set up, we can create our microservice. We'll start by creating a simple HelloController
:
@RestController
public class HelloController {
@RequestMapping("/")
public String index() {
return "Hello, world!";
}
}
This controller will map to the /
path, and it will return the string "Hello, world!" when called.
Now that we have our microservice created, we need to add a Dockerfile
to our project. A Dockerfile
is a text file that contains the instructions for building a Docker image.
Our Dockerfile
will be very simple. We'll start by specifying the base image that we want to use. For our example, we'll use the openjdk:8-jdk-alpine
image. This image contains a minimal version of Alpine Linux and the OpenJDK 8 JDK.
Next, we'll add a few lines to install the dependencies that our application needs:
FROM openjdk:8-jdk-alpine
RUN apk add --no-cache curl
We're using the apk
command to install the curl
command-line tool. curl
will be used later to make a request to our application to test that it's running.
Now, we'll add a few lines to copy our application jar file into the image, and to specify the command that should be run when the container is started:
FROM openjdk:8-jdk-alpine
RUN apk add --no-cache curl
COPY target/hello-world-0.0.1-SNAPSHOT.jar /hello-world.jar
ENTRYPOINT ["java", "-jar", "/hello-world.jar"]
Now that we have our Dockerfile
, we can build our Docker image. We'll use the docker build
command to build the image. We'll give our image the name "hello-world":
$ docker build -t hello-world .
Now that we have our Docker image, we can run our container. We'll use the docker run
command to run our container. We'll also specify the port that we want our container to run on. In our example, we'll use port 8080:
$ docker run -p 8080:8080 hello-world
Now that our container is running, we can test our application. We'll use the curl
command to make a request to our application:
$ curl http://localhost:8080
Hello, world!
In this article, we've seen how to use Spring Boot and Docker to develop and deploy microservices. We've seen how to create a simple microservice, how to build a Docker image for our service, and how to run our service in a Docker container.