Apache License

Apache License
Name	Apache License
Version	2.0
Author	Apache Software Foundation
Publisher	Apache Software Foundation
Published	January 2004
GPL compatible	GPLv3 only

Apache License. The Apache License is a permissive free software license authored by the Apache Software Foundation and widely adopted across the open-source software ecosystem. It grants users extensive rights to use, modify, and distribute software, with minimal restrictions, while providing explicit protection against patent litigation. The license is particularly noted for its clear terms regarding contributions and its compatibility with many other licensing models, making it a cornerstone for collaborative development in projects like the Apache HTTP Server and the Android operating system.

History and development

The license originated from the collaborative environment of the Apache Group, which formed in the mid-1990s to maintain the Apache HTTP Server. The original Apache License 1.0 was created to govern contributions to this project and other early efforts under the Apache Software Foundation. As the foundation's projects, such as the Apache Tomcat servlet container and the Apache Struts framework, grew in complexity and corporate involvement, the need for a more robust and legally precise document became apparent. This led to the drafting of Apache License 1.1, which included an explicit disclaimer of trademark rights, a clarification that proved important for commercial adoption. The evolution culminated in the comprehensive Apache License 2.0, drafted with significant input from the Free Software Foundation and the Open Source Initiative, to address modern concerns like software patents and international law.

License terms and conditions

The license grants recipients a perpetual, worldwide, non-exclusive, royalty-free license to the software's copyright and any applicable patent claims held by the contributors. Key provisions include the requirement to retain all original copyright, patent, trademark, and attribution notices in any redistributed code or substantial portions thereof. It includes a strong defensive termination clause, revoking a party's rights if they initiate any patent litigation claiming that the licensed work constitutes direct or contributory patent infringement. Unlike copyleft licenses such as the GNU General Public License, it imposes no obligation to release modifications under the same terms, allowing for integration into proprietary products. The license also includes a standard disclaimer of warranty and liability, common to most open-source licenses.

Compatibility with other licenses

Compatibility with other major licenses is a defining feature, especially its relationship with the GNU General Public License. The Free Software Foundation considers Apache License 2.0 compatible with version 3 of the GNU General Public License, meaning code under the two licenses can be combined in a larger work under GPLv3 terms. However, it is formally incompatible with GPLv2 due to patent retaliation clauses and indemnification requirements present in the Apache terms that are absent in the older GPL. It is broadly compatible with other permissive licenses like the MIT License and the BSD licenses, allowing for straightforward code mixing. This compatibility has been crucial for its adoption in massive projects like the Kubernetes orchestration system and the TensorFlow machine learning library.

Usage and adoption

Adoption is extensive, both within the projects of the Apache Software Foundation, such as Apache Cassandra and Apache Spark, and far beyond it. Major corporations, including Google, Microsoft, and IBM, use it for releasing open-source projects, valuing its clear patent protections and permissive nature. It is the default license for projects hosted on the Google Code platform and is the chosen license for foundational components of the Android Open Source Project. Its use in significant industry consortia, like the Cloud Native Computing Foundation for projects including Prometheus and Envoy, underscores its role as a standard for collaborative, enterprise-grade software development.

Version 2.0

Released in January 2004, this version represents a major rewrite to improve clarity, legal robustness, and international applicability. Key new features include an explicit, broad grant of patent rights from contributors to users, which was a direct response to rising concerns about software patent ambushes in open source. It simplified the required notice text for redistribution, moving away from the more cumbersome appendix system of Apache License 1.1. The license text itself was crafted to be more readable and to align with principles endorsed by the Open Source Initiative. It has since become the de facto standard for the foundation's projects and is overwhelmingly the most referenced version in the wider software industry.

Derivative works and contributions

The license provides explicit guidance on handling modifications and contributions, a critical aspect for collaborative projects. It states that any contributions intentionally submitted for inclusion in the licensed work shall be under the same terms, unless a separate agreement is attached. This provision, sometimes called a "patent peace" clause, helps ensure a coherent licensing status for the entire codebase. The treatment of derivative works is permissive; they may be distributed under different terms, including proprietary licenses, as long as the requirements for preserving notices and disclaimers are met. This flexibility has made it attractive for dual-licensing business models used by companies like MongoDB Inc. and for inclusion in commercial products from firms like Red Hat and Oracle Corporation.

Category:Free software licenses Category:Apache Software Foundation Category:2004 software