Remove legacy Prometheus metrics names. They were deprecated in Synapse v1.69.0 and disabled by default in Synapse v1.71.0. (#14538)

Author: reivilibre

Diff for: changelog.d/14538.removal

@@ -0,0 +1 @@
+Remove legacy Prometheus metrics names. They were deprecated in Synapse v1.69.0 and disabled by default in Synapse v1.71.0.

Diff for: docs/upgrade.md

@@ -88,6 +88,28 @@ process, for example:
     dpkg -i matrix-synapse-py3_1.3.0+stretch1_amd64.deb
     ```
 
+# Upgrading to v1.73.0
+
+## Legacy Prometheus metric names have now been removed
+
+Synapse v1.69.0 included the deprecation of legacy Prometheus metric names
+and offered an option to disable them.
+Synapse v1.71.0 disabled legacy Prometheus metric names by default.
+
+This version, v1.73.0, removes those legacy Prometheus metric names entirely.
+This also means that the `enable_legacy_metrics` configuration option has been
+removed; it will no longer be possible to re-enable the legacy metric names.
+
+If you use metrics and have not yet updated your Grafana dashboard(s),
+Prometheus console(s) or alerting rule(s), please consider doing so when upgrading
+to this version.
+Note that the included Grafana dashboard was updated in v1.72.0 to correct some
+metric names which were missed when legacy metrics were disabled by default.
+
+See [v1.69.0: Deprecation of legacy Prometheus metric names](#deprecation-of-legacy-prometheus-metric-names)
+for more context.
+
+
 # Upgrading to v1.72.0
 
 ## Dropping support for PostgreSQL 10

Diff for: docs/usage/configuration/config_documentation.md

@@ -2437,31 +2437,6 @@ Example configuration:
 enable_metrics: true
 ```
 ---
-### `enable_legacy_metrics`
-
-Set to `true` to publish both legacy and non-legacy Prometheus metric names,
-or to `false` to only publish non-legacy Prometheus metric names.
-Defaults to `false`. Has no effect if `enable_metrics` is `false`.
-**In Synapse v1.67.0 up to and including Synapse v1.70.1, this defaulted to `true`.**
-
-Legacy metric names include:
-- metrics containing colons in the name, such as `synapse_util_caches_response_cache:hits`, because colons are supposed to be reserved for user-defined recording rules;
-- counters that don't end with the `_total` suffix, such as `synapse_federation_client_sent_edus`, therefore not adhering to the OpenMetrics standard.
-
-These legacy metric names are unconventional and not compliant with OpenMetrics standards.
-They are included for backwards compatibility.
-
-Example configuration:
-```yaml
-enable_legacy_metrics: false
-```
-
-See https://github.com/matrix-org/synapse/issues/11106 for context.
-
-*Since v1.67.0.*
-
-**Will be removed in v1.73.0.**
----
 ### `sentry`
 
 Use this option to enable sentry integration. Provide the DSN assigned to you by sentry

Diff for: synapse/app/_base.py

@@ -266,26 +266,18 @@ async def wrapper() -> None:
     reactor.callWhenRunning(lambda: defer.ensureDeferred(wrapper()))
 
 
-def listen_metrics(
-    bind_addresses: Iterable[str], port: int, enable_legacy_metric_names: bool
-) -> None:
+def listen_metrics(bind_addresses: Iterable[str], port: int) -> None:
     """
     Start Prometheus metrics server.
     """
     from prometheus_client import start_http_server as start_http_server_prometheus
 
-    from synapse.metrics import (
-        RegistryProxy,
-        start_http_server as start_http_server_legacy,
-    )
+    from synapse.metrics import RegistryProxy
 
     for host in bind_addresses:
         logger.info("Starting metrics listener on %s:%d", host, port)
-        if enable_legacy_metric_names:
-            start_http_server_legacy(port, addr=host, registry=RegistryProxy)
-        else:
-            _set_prometheus_client_use_created_metrics(False)
-            start_http_server_prometheus(port, addr=host, registry=RegistryProxy)
+        _set_prometheus_client_use_created_metrics(False)
+        start_http_server_prometheus(port, addr=host, registry=RegistryProxy)
 
 
 def _set_prometheus_client_use_created_metrics(new_value: bool) -> None:

Diff for: synapse/app/generic_worker.py

@@ -320,7 +320,6 @@ def start_listening(self) -> None:
                     _base.listen_metrics(
                         listener.bind_addresses,
                         listener.port,
-                        enable_legacy_metric_names=self.config.metrics.enable_legacy_metrics,
                     )
             else:
                 logger.warning("Unsupported listener type: %s", listener.type)

Diff for: synapse/app/homeserver.py

@@ -265,7 +265,6 @@ def start_listening(self) -> None:
                     _base.listen_metrics(
                         listener.bind_addresses,
                         listener.port,
-                        enable_legacy_metric_names=self.config.metrics.enable_legacy_metrics,
                     )
             else:
                 # this shouldn't happen, as the listener type should have been checked

Diff for: synapse/config/metrics.py

@@ -43,8 +43,6 @@ class MetricsConfig(Config):
     def read_config(self, config: JsonDict, **kwargs: Any) -> None:
         self.enable_metrics = config.get("enable_metrics", False)
 
-        self.enable_legacy_metrics = config.get("enable_legacy_metrics", False)
-
         self.report_stats = config.get("report_stats", None)
         self.report_stats_endpoint = config.get(
             "report_stats_endpoint", "https://matrix.org/report-usage-stats/push"

Diff for: synapse/metrics/__init__.py

@@ -47,11 +47,7 @@
 # This module is imported for its side effects; flake8 needn't warn that it's unused.
 import synapse.metrics._reactor_metrics  # noqa: F401
 from synapse.metrics._gc import MIN_TIME_BETWEEN_GCS, install_gc_manager
-from synapse.metrics._legacy_exposition import (
-    MetricsResource,
-    generate_latest,
-    start_http_server,
-)
+from synapse.metrics._twisted_exposition import MetricsResource, generate_latest
 from synapse.metrics._types import Collector
 from synapse.util import SYNAPSE_VERSION
 
@@ -474,7 +470,6 @@ def register_threadpool(name: str, threadpool: ThreadPool) -> None:
     "Collector",
     "MetricsResource",
     "generate_latest",
-    "start_http_server",
     "LaterGauge",
     "InFlightGauge",
     "GaugeBucketCollector",