Azul Zulu OpenJDK vs. OpenJDK: A Complete Comparison

Problem Statement

When working with Java applications, developers often encounter multiple JDK distributions and wonder about the differences between them. A common point of confusion is understanding how Azul's Zulu offerings relate to the standard OpenJDK and what practical implications these differences have for development and production environments.

Java Specifications vs. Implementations

First, it's crucial to understand that Java is defined by a set of specifications (JSRs and JEPs) published by Oracle. These specifications are implemented in the source code found at the OpenJDK project, which serves as the reference implementation but is primarily just source code.

Several vendors provide builds of this OpenJDK source code, with varying levels of support, features, and licensing terms.

What is OpenJDK?

Key Fact

OpenJDK provides only source code - you cannot run Java applications directly with OpenJDK without first building the source into executables for your specific platform.

OpenJDK is the open-source foundation of the Java platform where the reference implementation is developed. It contains:

• Source code repositories for Java versions since JDK 6
• Collaboration space for Java Platform development
• No pre-built binaries or support services

Azul Systems and Zulu JDK

Azul Systems is a company specializing in Java and JVM products. Their Zulu offerings are builds of the OpenJDK source code:

Zulu Community

• Free distribution under GPLv2 with Classpath Exception (CPE) license
• Production-ready builds of OpenJDK
• Available for multiple platforms

Zulu Enterprise

• Commercial offering with support SLAs
• Guaranteed timely updates after Oracle releases patches
• Phone/email bug reporting and resolution
• Two versions of each update (CPU and PSU)

Zulu Embedded

• Specialized for embedded applications and constrained hardware
• Porting and support for specific chipsets
• Commercial product with free ARM 32 builds available

Key Differences and Similarities

Aspect	OpenJDK	Zulu Community	Zulu Enterprise
Source	Reference implementation	OpenJDK build	OpenJDK build
Cost	Free	Free	Commercial
Support	Community only	Community only	Professional SLA
Binaries	Not provided	Provided	Provided
Updates	As available	Timely	Guaranteed timely

Practical Implications

For most development purposes, Zulu Community behaves identically to other OpenJDK builds. Any Java application written to comply with Java specifications will run on Zulu products.

Additional Considerations

Special Features

Azul sometimes adds features not found in vanilla OpenJDK builds. For example, they back-ported Flight Recorder and Mission Control to their Java 8 version of Zulu products.

Emergency Patches

Vendors like Azul may apply critical bug or security fixes without waiting for official OpenJDK releases, providing faster response to vulnerabilities.

Java 17+ Licensing Changes

For Java 17 and later, Oracle JDK is available under a new No-Fee Terms and Conditions license, making production use free except for products sold while bundling Oracle JDK.

Choosing the Right JDK Distribution

Other JDK Providers

Besides Azul, several other vendors provide OpenJDK builds:

• Adoptium (formerly AdoptOpenJDK) - Community-driven builds
• Amazon - Corretto
• Microsoft - Microsoft Build of OpenJDK
• Red Hat - Red Hat build of OpenJDK
• IBM - IBM Semeru Runtime
• SAP - SAP Machine
• BellSoft - Liberica JDK

Conclusion

The relationship between OpenJDK, Azul Systems, and Zulu JDK can be summarized as:

• OpenJDK is the source code reference implementation
• Azul Systems is a company that provides Java solutions
• Zulu is Azul's binary distribution built from OpenJDK source

For most developers, Zulu Community provides a reliable, free OpenJDK build that's production-ready. Enterprises requiring support SLAs and guaranteed update timelines should consider Zulu Enterprise or other commercial offerings.

Always Verify

Regardless of which distribution you choose, always read the detailed license terms and requirements, as they can change between versions and vendors.

Additional Resources

• Java is Still Free - Comprehensive guide to Java licensing
• Azul Zulu Downloads - Official Zulu distributions
• OpenJDK Project - Official OpenJDK website