Add experimental configuration option to allow disabling legacy Prometheus metric names. (#13540)

Co-authored-by: David Robertson <davidr@element.io>

1 files changed, 284 insertions, 0 deletions

diff --git a/synapse/metrics/_legacy_exposition.py b/synapse/metrics/_legacy_exposition.py
new file mode 100644
index 0000000000..ff640a49af
--- /dev/null
+++ b/synapse/metrics/_legacy_exposition.py
@@ -0,0 +1,284 @@
+# Copyright 2015-2019 Prometheus Python Client Developers
+# Copyright 2019 Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+This code is based off `prometheus_client/exposition.py` from version 0.7.1.
+
+Due to the renaming of metrics in prometheus_client 0.4.0, this customised
+vendoring of the code will emit both the old versions that Synapse dashboards
+expect, and the newer "best practice" version of the up-to-date official client.
+"""
+
+import math
+import threading
+from http.server import BaseHTTPRequestHandler, HTTPServer
+from socketserver import ThreadingMixIn
+from typing import Any, Dict, List, Type, Union
+from urllib.parse import parse_qs, urlparse
+
+from prometheus_client import REGISTRY, CollectorRegistry
+from prometheus_client.core import Sample
+
+from twisted.web.resource import Resource
+from twisted.web.server import Request
+
+from synapse.util import caches
+
+CONTENT_TYPE_LATEST = "text/plain; version=0.0.4; charset=utf-8"
+
+
+def floatToGoString(d: Union[int, float]) -> str:
+    d = float(d)
+    if d == math.inf:
+        return "+Inf"
+    elif d == -math.inf:
+        return "-Inf"
+    elif math.isnan(d):
+        return "NaN"
+    else:
+        s = repr(d)
+        dot = s.find(".")
+        # Go switches to exponents sooner than Python.
+        # We only need to care about positive values for le/quantile.
+        if d > 0 and dot > 6:
+            mantissa = f"{s[0]}.{s[1:dot]}{s[dot + 1 :]}".rstrip("0.")
+            return f"{mantissa}e+0{dot - 1}"
+        return s
+
+
+def sample_line(line: Sample, name: str) -> str:
+    if line.labels:
+        labelstr = "{{{0}}}".format(
+            ",".join(
+                [
+                    '{}="{}"'.format(
+                        k,
+                        v.replace("\\", r"\\").replace("\n", r"\n").replace('"', r"\""),
+                    )
+                    for k, v in sorted(line.labels.items())
+                ]
+            )
+        )
+    else:
+        labelstr = ""
+    timestamp = ""
+    if line.timestamp is not None:
+        # Convert to milliseconds.
+        timestamp = f" {int(float(line.timestamp) * 1000):d}"
+    return "{}{} {}{}\n".format(name, labelstr, floatToGoString(line.value), timestamp)
+
+
+# Mapping from new metric names to legacy metric names.
+# We translate these back to their old names when exposing them through our
+# legacy vendored exporter.
+# Only this legacy exposition module applies these name changes.
+LEGACY_METRIC_NAMES = {
+    "synapse_util_caches_cache_hits": "synapse_util_caches_cache:hits",
+    "synapse_util_caches_cache_size": "synapse_util_caches_cache:size",
+    "synapse_util_caches_cache_evicted_size": "synapse_util_caches_cache:evicted_size",
+    "synapse_util_caches_cache_total": "synapse_util_caches_cache:total",
+    "synapse_util_caches_response_cache_size": "synapse_util_caches_response_cache:size",
+    "synapse_util_caches_response_cache_hits": "synapse_util_caches_response_cache:hits",
+    "synapse_util_caches_response_cache_evicted_size": "synapse_util_caches_response_cache:evicted_size",
+    "synapse_util_caches_response_cache_total": "synapse_util_caches_response_cache:total",
+}
+
+
+def generate_latest(registry: CollectorRegistry, emit_help: bool = False) -> bytes:
+    """
+    Generate metrics in legacy format. Modern metrics are generated directly
+    by prometheus-client.
+    """
+
+    # Trigger the cache metrics to be rescraped, which updates the common
+    # metrics but do not produce metrics themselves
+    for collector in caches.collectors_by_name.values():
+        collector.collect()
+
+    output = []
+
+    for metric in registry.collect():
+        if not metric.samples:
+            # No samples, don't bother.
+            continue
+
+        # Translate to legacy metric name if it has one.
+        mname = LEGACY_METRIC_NAMES.get(metric.name, metric.name)
+        mnewname = metric.name
+        mtype = metric.type
+
+        # OpenMetrics -> Prometheus
+        if mtype == "counter":
+            mnewname = mnewname + "_total"
+        elif mtype == "info":
+            mtype = "gauge"
+            mnewname = mnewname + "_info"
+        elif mtype == "stateset":
+            mtype = "gauge"
+        elif mtype == "gaugehistogram":
+            mtype = "histogram"
+        elif mtype == "unknown":
+            mtype = "untyped"
+
+        # Output in the old format for compatibility.
+        if emit_help:
+            output.append(
+                "# HELP {} {}\n".format(
+                    mname,
+                    metric.documentation.replace("\\", r"\\").replace("\n", r"\n"),
+                )
+            )
+        output.append(f"# TYPE {mname} {mtype}\n")
+
+        om_samples: Dict[str, List[str]] = {}
+        for s in metric.samples:
+            for suffix in ["_created", "_gsum", "_gcount"]:
+                if s.name == mname + suffix:
+                    # OpenMetrics specific sample, put in a gauge at the end.
+                    # (these come from gaugehistograms which don't get renamed,
+                    # so no need to faff with mnewname)
+                    om_samples.setdefault(suffix, []).append(sample_line(s, s.name))
+                    break
+            else:
+                newname = s.name.replace(mnewname, mname)
+                if ":" in newname and newname.endswith("_total"):
+                    newname = newname[: -len("_total")]
+                output.append(sample_line(s, newname))
+
+        for suffix, lines in sorted(om_samples.items()):
+            if emit_help:
+                output.append(
+                    "# HELP {}{} {}\n".format(
+                        mname,
+                        suffix,
+                        metric.documentation.replace("\\", r"\\").replace("\n", r"\n"),
+                    )
+                )
+            output.append(f"# TYPE {mname}{suffix} gauge\n")
+            output.extend(lines)
+
+        # Get rid of the weird colon things while we're at it
+        if mtype == "counter":
+            mnewname = mnewname.replace(":total", "")
+        mnewname = mnewname.replace(":", "_")
+
+        if mname == mnewname:
+            continue
+
+        # Also output in the new format, if it's different.
+        if emit_help:
+            output.append(
+                "# HELP {} {}\n".format(
+                    mnewname,
+                    metric.documentation.replace("\\", r"\\").replace("\n", r"\n"),
+                )
+            )
+        output.append(f"# TYPE {mnewname} {mtype}\n")
+
+        for s in metric.samples:
+            # Get rid of the OpenMetrics specific samples (we should already have
+            # dealt with them above anyway.)
+            for suffix in ["_created", "_gsum", "_gcount"]:
+                if s.name == mname + suffix:
+                    break
+            else:
+                sample_name = LEGACY_METRIC_NAMES.get(s.name, s.name)
+                output.append(
+                    sample_line(s, sample_name.replace(":total", "").replace(":", "_"))
+                )
+
+    return "".join(output).encode("utf-8")
+
+
+class MetricsHandler(BaseHTTPRequestHandler):
+    """HTTP handler that gives metrics from ``REGISTRY``."""
+
+    registry = REGISTRY
+
+    def do_GET(self) -> None:
+        registry = self.registry
+        params = parse_qs(urlparse(self.path).query)
+
+        if "help" in params:
+            emit_help = True
+        else:
+            emit_help = False
+
+        try:
+            output = generate_latest(registry, emit_help=emit_help)
+        except Exception:
+            self.send_error(500, "error generating metric output")
+            raise
+        self.send_response(200)
+        self.send_header("Content-Type", CONTENT_TYPE_LATEST)
+        self.send_header("Content-Length", str(len(output)))
+        self.end_headers()
+        self.wfile.write(output)
+
+    def log_message(self, format: str, *args: Any) -> None:
+        """Log nothing."""
+
+    @classmethod
+    def factory(cls, registry: CollectorRegistry) -> Type:
+        """Returns a dynamic MetricsHandler class tied
+        to the passed registry.
+        """
+        # This implementation relies on MetricsHandler.registry
+        #  (defined above and defaulted to REGISTRY).
+
+        # As we have unicode_literals, we need to create a str()
+        #  object for type().
+        cls_name = str(cls.__name__)
+        MyMetricsHandler = type(cls_name, (cls, object), {"registry": registry})
+        return MyMetricsHandler
+
+
+class _ThreadingSimpleServer(ThreadingMixIn, HTTPServer):
+    """Thread per request HTTP server."""
+
+    # Make worker threads "fire and forget". Beginning with Python 3.7 this
+    # prevents a memory leak because ``ThreadingMixIn`` starts to gather all
+    # non-daemon threads in a list in order to join on them at server close.
+    # Enabling daemon threads virtually makes ``_ThreadingSimpleServer`` the
+    # same as Python 3.7's ``ThreadingHTTPServer``.
+    daemon_threads = True
+
+
+def start_http_server(
+    port: int, addr: str = "", registry: CollectorRegistry = REGISTRY
+) -> None:
+    """Starts an HTTP server for prometheus metrics as a daemon thread"""
+    CustomMetricsHandler = MetricsHandler.factory(registry)
+    httpd = _ThreadingSimpleServer((addr, port), CustomMetricsHandler)
+    t = threading.Thread(target=httpd.serve_forever)
+    t.daemon = True
+    t.start()
+
+
+class MetricsResource(Resource):
+    """
+    Twisted ``Resource`` that serves prometheus metrics.
+    """
+
+    isLeaf = True
+
+    def __init__(self, registry: CollectorRegistry = REGISTRY):
+        self.registry = registry
+
+    def render_GET(self, request: Request) -> bytes:
+        request.setHeader(b"Content-Type", CONTENT_TYPE_LATEST.encode("ascii"))
+        response = generate_latest(self.registry)
+        request.setHeader(b"Content-Length", str(len(response)))
+        return response