What the SSPL Says and Why It Matters
MongoDB drafted the Server Side Public Licence in 2018 and submitted it to the Open Source Initiative for review. The SSPL's architecture resembles the GNU Affero General Public Licence — it extends copyleft to software run as a network service — but adds one critical clause: any organisation offering the covered software as a managed service must also open-source the entire stack supporting that service, including orchestration, monitoring, and provisioning tooling. The practical effect is not reciprocity but prohibition: running MongoDB as a cloud service without releasing everything around it is not a business model most companies can sustain.
The OSI's discussion process, which is public and conducted on its mailing lists, surfaced the core objection quickly. The Open Source Definition, maintained by the OSI, requires that a licence not restrict fields of endeavour or discriminate against specific uses. Critics — including Bruce Perens and Stefano Zacchiroli — argued that the SSPL's managed-services clause functions as a targeted restriction on cloud providers rather than a genuine reciprocity requirement. MongoDB withdrew the submission in 2019 without receiving approval.
The SSPL remained in use regardless. MongoDB continued to distribute its database under it, and in March 2024 Redis Ltd adopted it as one half of a dual-licence alongside RSALv2, ending Redis's long run under the BSD licence. In neither case did OSI non-approval prevent commercial adoption of the licence text; it simply kept the projects off any list that counts as open source by the canonical definition.
That gap between "source available" and "open source" is what the OSI's unapproved list actually enforces. A project carrying the SSPL is not closed: the source is readable, forkable in principle, and publicly posted. What it cannot be, under the OSI's framework, is called open source — a label that carries weight with corporate legal teams, procurement policies, and foundation membership criteria. For MongoDB and Redis Ltd, the trade was apparently acceptable: the SSPL deters the specific competitive threat, Amazon Web Services and its equivalents, at the cost of a classification that matters more to purists than to customers.
Whether the OSI's boundary is correctly drawn remains contested. What is not contested is where the line sits.