For a few turbulent years, "open source" quietly split in two. MongoDB, Elasticsearch, Terraform, Redis — some of the most depended-on infrastructure of the last decade — moved their code onto licenses the open-source community never approved. Then came the forks, then reported steps partway back. Through all of it, the substance of what most developers do with that code barely changed. But the boundary matters more than ever.
Here is what actually happened. MongoDB created the Server Side Public License and moved its code off open source onto it in 2018; the SSPL has never been OSI-approved. Elasticsearch and Kibana traded Apache 2.0 for dual licensing under the Elastic License and SSPL in January 2021. HashiCorp switched Terraform from the Mozilla Public License 2.0 to the Business Source License in August 2023 — not retroactively, so older releases kept their MPL terms. Redis, long under the permissive BSD license, moved with Redis 7.4 to a dual RSALv2/SSPLv1 setup. In each case, the community answered with a fork: OpenTofu under the Linux Foundation, and Valkey, a BSD-licensed fork, launched in March 2024.
The pattern is not coincidence. Each of these licenses is permissive in almost every way — read the source, use it, even sell software on top of it — except for one carve-out: you cannot host the thing as a competing service. That single clause is the whole reason the stewards switched. It shields them from cloud providers who would otherwise resell their work as a service, and it lets them sell that right themselves.
So for most of us, nothing real changed. Your application still runs on the same code with the same API. What changed is a promise. "You can read the source" quietly stopped meaning "you can build on it." And because source-available looks so close to open source, a lot of engineering teams never noticed the swap until a fork appeared.
The small comebacks are worth watching. Redis added OSI-approved AGPLv3 back as a third option in later releases, and Elastic did the same in September 2024. These are deliberate steps toward OSI-approved openness, and they hint the pendulum may swing partway home.
And WordPress is a reminder this was never only about code. It's GPL, proudly open source — yet in October 2024 WP Engine sued Automattic and Matt Mullenweg over trademark demands, after Mullenweg had reportedly called WP Engine a cancer and barred it from wordpress.org. Open code does not shield you from licensing and trademark conflict at the edges.
So check the license before you bet your infrastructure on a tool. Know what the licenses on your own project actually allow. And do not mistake "you can read the source" for "you can build on it." The license name on a README has always mattered. These days it matters more, because the license has become part of the product.