Source-Available Licenses: BSL, SSPL, FSL, ELv2

Source-available licenses let anyone read, run and modify a project's code but restrict one use, usually offering it as a competing paid service. The Business Source License (BSL), Server Side Public License (SSPL), Functional Source License (FSL) and Elastic License 2.0 (ELv2) all work this way, and none of them is an open source license under the Open Source Definition. As of October 2026, the main differences are what each one forbids and whether the code eventually becomes open source.

This guide is a plain-language summary, not legal advice. Read the actual license text, or ask a lawyer, before building a product on top of any of them.

Source-available vs open source

An open source license, as defined by the Open Source Initiative, cannot discriminate against fields of endeavour. That includes commercial cloud hosting. A source-available license publishes the code but adds a restriction that breaks that rule, so the project is not "open source" even though you can read every line.

The licenses below were mostly adopted for the same reason: vendors that build a database or infrastructure product did not want cloud providers to resell it as a managed service. The trade-off falls on users, who get code they can inspect but with limits on what they can do with it. Our Open Source coverage follows the projects that moved in either direction.

Business Source License (BSL 1.1)

The BSL was written by MariaDB. Each licensor fills in three parameters, which is why two BSL projects can behave very differently.

Additional Use Grant: the production uses the licensor allows for free, for example anything except a competing hosted offering.
Change Date: the point at which a given version converts to a more permissive license. Under MariaDB's adoption FAQ, conversion happens no later than the fourth anniversary of a version's first public distribution.
Change License: the license the code becomes. MariaDB says it must be GPL version 2 or later, or a compatible license.

MariaDB states plainly that the BSL is not an open source license. Because conversion is tied to each version, old releases become open source on a rolling basis while the latest ones stay restricted.

The best-known case is HashiCorp. On August 10, 2023 it moved future releases of its products from MPL 2.0 to BSL 1.1, with an exception for providing a competitive offering to HashiCorp. The community responded with a fork that became OpenTofu, now maintained under the Linux Foundation.

Server Side Public License (SSPL)

MongoDB created the SSPL, and it applies to MongoDB Community Server releases made on or after October 16, 2018; earlier versions remain under AGPL v3.0, according to MongoDB's FAQ. It is based on GPLv3 and adds Section 13.

Section 13 applies if you offer the software to third parties as a service. You must then release the "Service Source Code" under the SSPL. That covers not only your modifications but the management software, user interfaces, APIs, automation, monitoring, backup and hosting software needed to run the service. MongoDB says that internal use, and applications that merely use MongoDB as their database, are not caught.

The SSPL has no automatic conversion date, and it is not OSI-approved.

Elastic License 2.0 (ELv2)

Elastic announced ELv2 in early 2021 when it moved Elasticsearch and Kibana away from Apache 2.0. The license is short and has three limits. You may not:

provide the software to others as a managed service;
circumvent license-key functionality or remove features protected by keys;
remove or obscure licensing or copyright notices.

Like the SSPL, ELv2 has no conversion date. Its restriction is also narrower than the SSPL's: it forbids the managed-service use outright instead of requiring you to publish your whole stack.

Functional Source License (FSL)

The FSL was introduced by Sentry on November 17, 2023, after the company had spent several years on the BSL. According to the FSL site, you can use the software for any purpose except undermining its producer, and each version converts to Apache 2.0 or MIT after two years.

Unlike the BSL, the FSL has no custom Additional Use Grant to negotiate and a fixed two-year conversion. The two variants are named FSL-1.1-ALv2 (Apache 2.0) and FSL-1.1-MIT. Sentry's own notes say it is best suited to SaaS businesses, not products sold for on-premise use or embedding.

Side-by-side comparison

BSL 1.1: restriction set by each licensor; converts after a date chosen by the licensor, at most four years; change license GPL-compatible; not OSI-approved.
SSPL: offering the software as a service requires publishing the full service stack under the SSPL; no conversion; not OSI-approved.
ELv2: no managed-service offering, no tampering with license keys or notices; no conversion; not OSI-approved.
FSL: no competing use; converts to Apache 2.0 or MIT after two years; not OSI-approved.

When projects change course

Relicensing is not always one-way. Elastic announced on August 29, 2024 that it would add the AGPL as an option for Elasticsearch and Kibana alongside ELv2 and SSPL, saying the two products could be called open source again.

Redis followed a similar path. It moved to dual source-available licensing in March 2024, then added the OSI-approved AGPLv3 as an option with Redis 8 in May 2025. Redis itself noted that the SSPL change hurt its relationship with the community, and that AWS and Google maintain their own fork.

The pattern matters for anyone choosing dependencies. A vendor-controlled license can change for future releases, so check which license applies to the exact version you deploy. Our developer coverage and Big Tech reporting track how cloud providers respond.

How to choose as a user

If you only run the software internally or inside your own product, most of these licenses leave you alone, but confirm with the exact text.
If you plan to host it for customers, the SSPL, ELv2, BSL and FSL can all block or complicate that.
If you need guarantees that the code will be open source later, prefer BSL or FSL, which have a conversion clock.

Frequently asked questions

Is the Business Source License open source?

No. MariaDB, the license's author, says the BSL is not an open source license, although it does meet many of the Open Source Definition's criteria. Each version converts to a GPL-compatible license after the change date.

What is the difference between SSPL and AGPL?

Both require source sharing when you provide software over a network. The SSPL goes further: it requires you to release the source of the entire service stack, including management and hosting software, and it is not OSI-approved, while the AGPL is.

How long until FSL code becomes open source?

Two years after each version is made available, when it converts to Apache 2.0 or MIT depending on the variant the project chose.

Can I use ELv2 software in my company?

Generally yes for your own use, but you cannot offer it to others as a managed service or tamper with license-key features. Check the full text for your case.

Did Redis go back to open source?

Partly. Since Redis 8 in May 2025 the AGPLv3, which is OSI-approved, is offered as an additional licensing option next to the source-available ones.