SSPL is MongoDB’s response to the AGPL “loophole”: if you offer the software as a managed service, you must also release under SSPL the source code of every program you use to offer that service — provisioning, monitoring, orchestration, backup. In effect, it is strong copyleft extended to your service stack.
The OSI rejected SSPL as not meeting the Open Source Definition, specifically on Criterion 6 (no discrimination against fields of endeavour). It is therefore fair-code / source-available, not open source.
How to apply
Add a LICENSE file with the full SSPL-1.0 text. Each source file should carry:
// SPDX-License-Identifier: SSPL-1.0
Full license text
SERVER SIDE PUBLIC LICENSE
Version 1, October 16, 2018
Copyright © 2018 MongoDB, Inc.
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
TERMS AND CONDITIONS
0. Definitions.
1. Source Code.
2. Basic Permissions.
3. Protecting Users' Legal Rights From Anti-Circumvention Law.
4. Conveying Verbatim Copies.
5. Conveying Modified Source Versions.
6. Conveying Non-Source Forms.
7. Additional Terms.
8. Termination.
9. Acceptance Not Required for Having Copies.
10. Automatic Licensing of Downstream Recipients.
11. Patents.
12. No Surrender of Others' Freedom.
13. Offering the Program as a Service.
If you make the functionality of the Program or a modified version
available to third parties as a service, you must make the Service
Source Code available via network download to everyone at no charge,
under the terms of this License. "Service Source Code" means the
Corresponding Source for the Program or the modified version, and
the Corresponding Source for all programs that you use to make the
Program or modified version available as a service, including,
without limitation, management software, user interfaces,
application program interfaces, automation software, monitoring
software, backup software, storage software and hosting software,
all such that a user could run an instance of the service using
the Service Source Code you make available.
14. Revised Versions of this License.
15. Disclaimer of Warranty.
16. Limitation of Liability.
17. Interpretation of Sections 15 and 16.
END OF TERMS AND CONDITIONS
… this text is abbreviated.
For the complete license text, see
https://www.mongodb.com/licensing/server-side-public-license
Raw text also available at /license-texts/SSPL-1.0.txt — handy for curl.