Add deprecation policy doc (#9723)

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

1 files changed, 33 insertions, 0 deletions

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+Deprecation Policy for Platform Dependencies
+============================================
+
+Synapse has a number of platform dependencies, including Python and PostgreSQL.
+This document outlines the policy towards which versions we support, and when we
+drop support for versions in the future.
+
+
+Policy
+------
+
+Synapse follows the upstream support life cycles for Python and PostgreSQL,
+i.e. when a version reaches End of Life Synapse will withdraw support for that
+version in future releases.
+
+Details on the upstream support life cycles for Python and PostgreSQL are
+documented at https://endoflife.date/python and
+https://endoflife.date/postgresql.
+
+
+Context
+-------
+
+It is important for system admins to have a clear understanding of the platform
+requirements of Synapse and its deprecation policies so that they can
+effectively plan upgrading their infrastructure ahead of time. This is
+especially important in contexts where upgrading the infrastructure requires
+auditing and approval from a security team, or where otherwise upgrading is a
+long process.
+
+By following the upstream support life cycles Synapse can ensure that its
+dependencies continue to get security patches, while not requiring system admins
+to constantly update their platform dependencies to the latest versions.