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https://issues.apache.org/jira/browse/CAMEL-23080?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18061195#comment-18061195
]
Claus Ibsen commented on CAMEL-23080:
-------------------------------------
**Yes, you can deploy a Spring Boot application inside an existing (external)
Tomcat server**, and this remains a fully supported and commonly used approach
even in 2026.
Spring Boot applications are **not** limited to their embedded Tomcat — you can
package them as a standard **WAR** file and deploy them to an external Tomcat
instance (or other servlet containers like Jetty, Undertow, WebLogic, etc.)
just like a classic Spring MVC or Java EE application.
### Key Differences: Embedded vs. External Tomcat
| Aspect | Embedded Tomcat (default Spring Boot JAR)
| External Tomcat (WAR deployment) |
|-------------------------|------------------------------------------------------------|-----------------------------------------------------------|
| Packaging | Executable JAR
| WAR file |
| Server startup | `java -jar myapp.jar` — starts its own Tomcat
| Tomcat starts → deploys and manages your app |
| Configuration | Mostly via `application.properties/yaml`
| Tomcat-level config (ports, SSL, realms, etc.) + app config |
| Use case | Microservices, containers (Docker/K8s), standalone
apps | Traditional enterprise setups, shared Tomcat instances, legacy
migration |
| Pros | Zero server install, easy dev/test, fast startup
| Centralized management, monitoring, multiple apps per server |
| Cons | Less control over container lifecycle
| More setup steps, potential version conflicts |
### How to Make Your Spring Boot App Deployable to External Tomcat
Here are the minimal changes (works with Spring Boot 2.x and 3.x):
1. **Change packaging to WAR** (in `pom.xml` for Maven):
```xml
<packaging>war</packaging>
```
Or in `build.gradle` (Gradle):
```groovy
apply plugin: 'war'
```
2. **Mark the embedded Tomcat as provided** (so it isn't packaged into your WAR
and avoids conflicts):
```xml
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<scope>provided</scope> <!-- ← this is the key line -->
</dependency>
```
3. **Extend `SpringBootServletInitializer`** (this makes your app compatible
with servlet containers):
```java
import
org.springframework.boot.web.servlet.support.SpringBootServletInitializer;
import org.springframework.boot.builder.SpringApplicationBuilder;
@SpringBootApplication
public class MyApplication extends SpringBootServletInitializer {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args); // still works
for local dev with JAR
}
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder
application) {
return application.sources(MyApplication.class);
}
}
```
4. **Build the WAR**:
```
mvn clean package
```
→ You'll get `target/your-app-1.0.0.war` (or similar)
5. **Deploy to Tomcat**:
- Copy the `.war` file to Tomcat's `webapps/` directory
- Start/restart Tomcat (`bin/startup.sh` or `.bat`)
- Your app will be available at `http://localhost:8080/your-app-name/...`
(context path = WAR filename unless renamed)
Optional: Rename the WAR to `ROOT.war` → deploys at root context `/`
### Important Notes (2026 perspective)
- This method works perfectly with **Tomcat 9, 10, and 11** (Tomcat 10+
requires Jakarta EE migration if you're on older Spring Boot versions — use
Spring Boot 3.x for full compatibility).
- Many large organizations still use this pattern for centralized ops, shared
Tomcat clusters, or gradual migration from legacy Spring apps.
- For new greenfield projects, most teams prefer the **embedded server +
Docker/Kubernetes** approach — it's simpler and more cloud-native.
- If you're hitting issues (e.g., 404s, class conflicts), check Tomcat logs
(`logs/catalina.out`) — common culprits are missing
`SpringBootServletInitializer` or duplicate Tomcat jars.
> camel-jbang - Add Tomcat as a runtime
> -------------------------------------
>
> Key: CAMEL-23080
> URL: https://issues.apache.org/jira/browse/CAMEL-23080
> Project: Camel
> Issue Type: New Feature
> Components: camel-jbang
> Reporter: Claus Ibsen
> Priority: Major
> Fix For: 4.x
>
>
> We can export to SB Q and main. But it would also be nice to export to
> tomcat, which is essentially SB packaged as WAR and embedded on Tomcat. That
> is a common practice to run many apps in the same JVM.
>
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