ADR-005: Apache Tomcat as Servlet Container

Decision Analysis and Resolution: SW360 Servlet Container

Created by: SW360 Architecture Team
Original Decision: 2014
Reformatted: April 2026
Status: Accepted
Estimated read time: 8 minutes

Table of Contents

1. Background
2. Goal
3. Key Principles
4. Key Inputs, Assumptions and Restrictions
5. Options Analysis
   • Option 1 - Apache Tomcat
   • Option 2 - Eclipse Jetty
   • Option 3 - WildFly/JBoss
   • Option 4 - GlassFish
6. Criteria for Making a Decision
7. Final Decision
8. Evolution
9. Contributors

Background

SW360 was originally designed as a Liferay Portal application, which required a servlet container to host web applications. The servlet container needed to:

• Host the Liferay portal WAR and portlet applications
• Support multiple web applications (portlets, REST services)
• Provide standard Java EE/Jakarta EE servlet capabilities
• Enable production-grade deployment with proven reliability
• Integrate well with Spring-based applications

Why This Decision Matters: The servlet container is the runtime foundation for all SW360 web components, affecting deployment, performance, and operational aspects.

Goal

The goal of this decision analysis is to:

1. Select a servlet container that supports Liferay Portal deployment
2. Enable reliable production deployments
3. Support future Spring Boot integration
4. Minimize operational complexity

Key Principles

Key Inputs, Assumptions and Restrictions

Options Analysis

Option 1 - Apache Tomcat

Summary

Use Apache Tomcat, the most widely deployed open-source servlet container. Lightweight, reliable, and the recommended platform for both Liferay Portal and Spring Boot applications.

Conceptual View

graph TB
    subgraph Tomcat["Apache Tomcat"]
        direction TB
        W["webapps/<br/>├── liferay-portal.war<br/>├── sw360-rest.war<br/>└── sw360-thrift.war"]
        C["Connectors: HTTP/AJP<br/>Thread Pool: Configurable<br/>JNDI: Database connections"]
    end

Impact / Changes Required

• Deploy WAR files to webapps directory
• Configure server.xml for connectors and resources
• Tune thread pools for production load

SWOT Analysis

Option 2 - Eclipse Jetty

Summary

Use Eclipse Jetty, a lightweight, embeddable servlet container known for its small footprint and fast startup time.

Conceptual View

graph TB
    subgraph Jetty["Eclipse Jetty"]
        direction TB
        J1["Embedded or standalone"]
        J2["WebSocket native support"]
        J3["HTTP/2 support"]
    end

Impact / Changes Required

• Configure Jetty for Liferay deployment
• Different configuration format than Tomcat
• May need additional modules for features

SWOT Analysis

Option 3 - WildFly/JBoss

Summary

Use WildFly (formerly JBoss AS), a full Java EE application server providing comprehensive enterprise features including EJB, JMS, and clustering.

Conceptual View

graph TB
    subgraph WF["WildFly/JBoss"]
        direction TB
        W1["Full Java EE stack"]
        W2["EJB, JMS, CDI, JPA"]
        W3["Clustering built-in"]
    end

Impact / Changes Required

• Deploy as EAR or WAR
• Configure subsystems for features
• Larger infrastructure footprint

SWOT Analysis

Option 4 - GlassFish

Summary

Use GlassFish, the reference implementation for Java EE/Jakarta EE specifications.

Conceptual View

┌────────────────────────────────────────────────┐
│               GlassFish                         │
├────────────────────────────────────────────────┤
│  Jakarta EE reference implementation            │
│  Full specification support                     │
└────────────────────────────────────────────────┘

Impact / Changes Required

• Deploy as WAR/EAR
• Configure admin console
• Learn GlassFish administration

SWOT Analysis

Criteria for Making a Decision

T-Shirt Sizing Scale

Weighted Evaluation Matrix

Score Summary

Final Decision

Selected Option: Apache Tomcat

Rationale

Apache Tomcat was selected as the servlet container for SW360 based on:

1. Highest Weighted Score (637.5) - Clear winner across all criteria

2. Liferay Compatibility (XL) - Official recommendation:

   • Liferay Portal is tested extensively on Tomcat
   • Liferay documentation assumes Tomcat
   • Best integration and support

3. Spring Boot Integration (XL) - Future-proof:

   • Spring Boot embeds Tomcat by default
   • Seamless transition from external to embedded deployment
   • Same runtime in development and production

4. Operations Familiarity (XL) - Lower risk:

   • Most widely deployed servlet container
   • Operations teams have Tomcat experience
   • Abundant monitoring and management tools

5. Production Reliability (XL) - Battle-tested:

   • Powers major applications worldwide
   • Proven stability and scalability
   • Well-understood performance characteristics

Current Configuration (Spring Boot 3.x)

# Embedded Tomcat is auto-configured by Spring Boot
server.port=8080
server.tomcat.threads.max=200
server.tomcat.threads.min-spare=10
server.tomcat.accept-count=100

Evolution

Servlet Container Version History

Deployment Model Evolution

Related Decisions

• ADR-001: Thrift services coexist with Tomcat servlet handling
• ADR-004: Spring Boot 3.x migration (Tomcat 11.x embedded)

Contributors

Consequences Summary

Positive

• ✅ Standard deployment model—WAR deployment familiar to Java operations
• ✅ Mature ecosystem—extensive tooling, monitoring, documentation
• ✅ Spring Boot default—embedded Tomcat simplifies modern deployments
• ✅ Stable APIs—servlet specification is backward compatible
• ✅ Team expertise—operations team knows Tomcat

Negative

• ⚠️ Configuration tuning required for production
• ⚠️ Memory footprint heavier than Jetty for simple apps
• ⚠️ Version coupling with Jakarta EE requirements

Neutral

• Jakarta EE migration—Tomcat 10+ uses jakarta.* namespace
• Both embedded and external deployment modes supported

Revision History