Blog · Licensing

Open source vs source available

Q: What's the difference between open source and source available?

Open source (per the OSI definition) means anyone can read, modify, and redistribute the code for any purpose, including commercial use. Source available means you can read the code but there are restrictions on commercial use. The BSL, SSPL, and Elastic License are source-available but not open source.

Q: Is the Business Source License (BSL) open source?

No, not by the OSI definition. BSL restricts competitive use of the code while it's in the BSL period (typically 3-4 years), then converts to Apache 2.0 (which IS open source). HashiCorp uses BSL for Terraform, Vault, and Consul. After the BSL period, the code becomes fully open source.

Q: Why did MongoDB and Elastic move away from open source?

Both companies were concerned that cloud providers (AWS, Google Cloud, Azure) were monetizing their work without contributing back. MongoDB moved to SSPL in 2018. Elastic moved to the Elastic License in 2021. Both have open source alternatives (MongoDB has DocumentDB, Elasticsearch has OpenSearch) that the cloud providers can use. The licensing change was a way to monetize the cloud version while keeping the code source-available.

Q: Can I adopt a project that's under BSL or SSPL?

It's much harder than adopting a MIT/Apache project. For BSL: wait for the conversion period (typically 3-4 years). For SSPL: there's no easy adoption path — the license is designed to prevent forks that compete with the original. For most adoption scenarios, MIT/Apache/GPL are much easier.

BSL, SSPL, Elastic — the new wave of source-available licenses. How they differ from open source, why HashiCorp and MongoDB moved, and what it means for adoption.

Published July 13, 2026 · ~5 min read

The 30-second version

Open source (per the OSI definition) = anyone can read, modify, and redistribute the code for any purpose, including commercial use.
Source available = you can read the code but there are restrictions on commercial use.
The BSL, SSPL, and Elastic License are source-available but NOT open source.

The three source-available licenses that matter in 2026

BSL — Business Source License

Used by HashiCorp for Terraform, Vault, and Consul. The structure: the code is BSL-licensed for 3-4 years, then converts to Apache 2.0 (which IS open source). During the BSL period, the restriction is: you can use the code for your own purposes, but you can't sell a competing product. After conversion, the code becomes fully open source. This is the "delayed open source" model — companies get a few years to monetize, then the code opens up.

SSPL — Server Side Public License

MongoDB's license since 2018. The restriction: if you offer the software as a service, you must publish the source of your entire service stack (not just the MongoDB parts). This is designed to make it impossible for cloud providers to offer MongoDB-as-a-service without publishing their own service code. Most companies avoid SSPL-licensed code because the service-stack requirement is unworkable.

Elastic License

Elastic's license since 2021. The restriction: you can use Elasticsearch for your own purposes, but you can't offer it as a hosted service. AWS (which had been offering Elasticsearch as a service) responded by forking Elasticsearch into OpenSearch. The Elastic License is more permissive than SSPL but more restrictive than BSL — it allows most internal use, just not the cloud-provider use case.

What this means for adoption

Adopting a source-available project is much harder than adopting an open source one:

BSL: wait for the conversion period (3-4 years) or get an exception from the original maintainer.
SSPL: the license is designed to prevent the most likely adoption scenarios. Adoption is rare.
Elastic License: you can adopt the code, but you can't offer it as a service. This rules out cloud-provider adoption but allows internal use.

For most maintainers stepping back, the answer is still MIT or Apache 2.0 — the frictionless handoff model. The 41% revival rate from the 2019 arXiv study assumes a permissive license. With a source-available license, the rate is much lower.

Frequently asked questions

What's the difference between open source and source available?

Open source = any use. Source available = restrictions on commercial use.

Is the BSL open source?

Not by the OSI definition during the BSL period. It converts to Apache 2.0 after 3-4 years.

Why did MongoDB and Elastic move away from open source?

Cloud providers monetized their work without contributing back.

Can I adopt a project that's under BSL or SSPL?

Much harder than MIT/Apache. For BSL, wait for conversion. For SSPL, adoption is rare.