1.22.0 (pending)

Incompatible Behavior Changes

Changes that are expected to cause an incompatibility if applicable; deployment changes are likely required

tls: set TLS v1.2 as the default minimal version for servers. Users can still explicitly opt-in to 1.0 and 1.1 using :ref:`tls_minimum_protocol_version <envoy_v3_api_field_extensions.transport_sockets.tls.v3.TlsParameters.tls_minimum_protocol_version>`.

Changes that may cause incompatibilities for some users, but should not for most

grpc: flip runtime guard envoy.reloadable_features.enable_grpc_async_client_cache to be default enabled. async grpc client created through getOrCreateRawAsyncClient will be cached by default.
http: now the max concurrent streams of http2 connection can not only be adjusted down according to the SETTINGS frame but also can be adjusted up, of course, it can not exceed the configured upper bounds. This fix is guarded by envoy.reloadable_features.http2_allow_capacity_increase_by_settings.

Changes expected to improve the state of the world and are unlikely to have negative effects

data plane: fixing error handling where writing to a socket failed while under the stack of processing. This should genreally affect HTTP/3. This behavioral change can be reverted by setting envoy.reloadable_features.allow_upstream_inline_write to false.

http: removed envoy.reloadable_features.hash_multiple_header_values and legacy code paths.
http: removed envoy.reloadable_features.require_strict_1xx_and_204_response_headers and envoy.reloadable_features.send_strict_1xx_and_204_response_headers and legacy code paths.
http: removed envoy.reloadable_features.strip_port_from_connect and legacy code paths.
http: removed envoy.reloadable_features.use_observable_cluster_name and legacy code paths.

http3: downstream HTTP/3 support is now GA! Upstream HTTP/3 also GA for specific deployments. See :ref:`here <arch_overview_http3>` for details.

http: removing support for long-deprecated old style filter names, e.g. envoy.router, envoy.lua.