tcp: switching to the new pool (#16465)

Risk Level: High (new tcp pool, lots of smoke testing)
Testing: integration tests, unit tests, production validation by Pinterest
Docs Changes: n/a
Release Notes: inline

Signed-off-by: Alyssa Wilk <alyssar@chromium.org>

docs/root/version_history/current.rst

@@ -31,7 +31,7 @@ Minor Behavior Changes
 * http: serve HEAD requests from cache.
 * listener: respect the :ref:`connection balance config <envoy_v3_api_field_config.listener.v3.Listener.connection_balance_config>`
   defined within the listener where the sockets are redirected to. Clear that field to restore the previous behavior.
-
+* tcp: switched to the new connection pool by default. Any unexpected behavioral changes can be reverted by setting runtime guard ``envoy.reloadable_features.new_tcp_connection_pool`` to false.
 
 
 Bug Fixes
@@ -68,6 +68,7 @@ New Features
 * http: added upstream and downstream alpha HTTP/3 support! See :ref:`quic_options <envoy_v3_api_field_config.listener.v3.UdpListenerConfig.quic_options>` for downstream and the new http3_protocol_options in :ref:`http_protocol_options <envoy_v3_api_msg_extensions.upstreams.http.v3.HttpProtocolOptions>` for upstream HTTP/3.
 * listener: added ability to change an existing listener's address.
 * metric service: added support for sending metric tags as labels. This can be enabled by setting the :ref:`emit_tags_as_labels <envoy_v3_api_field_config.metrics.v3.MetricsServiceConfig.emit_tags_as_labels>` field to true.
+* tcp: added support for :ref:`preconnecting <v1.18.0:envoy_v3_api_msg_config.cluster.v3.Cluster.PreconnectPolicy>`. Preconnecting is off by default, but recommended for clusters serving latency-sensitive traffic.
 * udp_proxy: added :ref:`key <envoy_v3_api_msg_extensions.filters.udp.udp_proxy.v3.UdpProxyConfig.HashPolicy>` as another hash policy to support hash based routing on any given key.
 
 Deprecated

source/common/runtime/runtime_features.cc

@@ -76,6 +76,7 @@ constexpr const char* runtime_features[] = {
     "envoy.reloadable_features.http2_skip_encoding_empty_trailers",
     "envoy.reloadable_features.improved_stream_limit_handling",
     "envoy.reloadable_features.internal_redirects_with_body",
+    "envoy.reloadable_features.new_tcp_connection_pool",
     "envoy.reloadable_features.prefer_quic_kernel_bpf_packet_routing",
     "envoy.reloadable_features.preserve_downstream_scheme",
     "envoy.reloadable_features.remove_forked_chromium_url",
@@ -106,8 +107,6 @@ constexpr const char* runtime_features[] = {
 constexpr const char* disabled_runtime_features[] = {
     // v2 is fatal-by-default.
     "envoy.test_only.broken_in_production.enable_deprecated_v2_api",
-    // TODO(alyssawilk) flip true after the release.
-    "envoy.reloadable_features.new_tcp_connection_pool",
     // TODO(asraa) flip to true in a separate PR to enable the new JSON by default.
     "envoy.reloadable_features.remove_legacy_json",
     // Sentinel and test flag.