Embedded server trong Spring Boot là gì và tại sao hữu ích?

Spring Boot nhúng web server (Tomcat default, Jetty, Undertow) trực tiếp vào JAR — không cần deploy lên app server ngoài.

java -jar app.jar   # chạy, không cần Tomcat/JBoss/WildFly cài sẵn

Lợi ích:
- 1 artifact duy nhất (JAR chứa cả code + server).
- Environment consistency — dev/staging/prod cùng runtime.
- Container-friendly — Docker/Kubernetes chỉ cần JDK + JAR.
- Operations đơn giản — không quản lý app server riêng.

Đổi server:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
  <exclusions>
    <exclusion>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-tomcat</artifactId>
    </exclusion>
  </exclusions>
</dependency>
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

Cấu hình: server.port=8080, server.servlet.context-path=/api.

Trade-off: mỗi service có Tomcat riêng (tốn memory hơn vs shared server truyền thống) — chấp nhận được cho microservices, cloud-native.

Spring Boot embeds the web server (Tomcat by default, Jetty, Undertow) directly into the JAR — no external app server to deploy to.

java -jar app.jar   # runs, no pre-installed Tomcat/JBoss/WildFly

Benefits:
- A single artifact (JAR contains code + server).
- Environment consistency — same runtime in dev/staging/prod.
- Container-friendly — Docker/Kubernetes only need JDK + JAR.
- Simple ops — no separate app server to manage.

Switching servers:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
  <exclusions>
    <exclusion>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-tomcat</artifactId>
    </exclusion>
  </exclusions>
</dependency>
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

Configuration: server.port=8080, server.servlet.context-path=/api.

Trade-off: each service has its own Tomcat (more memory than a shared traditional server) — acceptable for microservices and cloud-native apps.