feat: add opentelemetry service

It's only useful for metrics, but it adds the core of tracing and
logging.

pyms/flask/app/create_app.py

@@ -80,6 +80,7 @@ def example():
     request: Optional[DriverService] = None
     tracer: Optional[DriverService] = None
     metrics: Optional[DriverService] = None
+    opentelemetry: Optional[DriverService] = None
     _singleton = True
 
     def __init__(self, *args, **kwargs):
@@ -204,6 +205,28 @@ def init_metrics(self) -> None:
             )
             self.metrics.monitor(self.application.config["APP_NAME"], self.application)
 
+    def init_opentelemetry(self) -> None:
+        if self.opentelemetry:
+            if self.opentelemetry.config.metrics.enabled:
+                # Set metrics backend
+                self.opentelemetry.set_metrics_backend()
+                # Set the metrics blueprint
+                # DISCLAIMER this endpoint may be only necessary with prometheus client
+                self.application.register_blueprint(self.opentelemetry.blueprint)
+                # Set instrumentations
+                if self.opentelemetry.config.metrics.instrumentations.flask:
+                    self.opentelemetry.monitor(
+                        self.application.config["APP_NAME"], self.application
+                    )
+                if self.opentelemetry.config.metrics.instrumentations.logger:
+                    self.opentelemetry.add_logger_handler(
+                        self.application.logger, self.application.config["APP_NAME"]
+                    )
+            if self.opentelemetry.config.tracing.enabled:
+                self.opentelemetry.set_tracing_backend()
+            if self.opentelemetry.config.logging.enabled:
+                self.opentelemetry.set_logging_backend()
+
     def reload_conf(self):
         self.delete_services()
         self.config.reload()
@@ -237,6 +260,8 @@ def create_app(self) -> Flask:
 
         self.init_metrics()
 
+        self.init_opentelemetry()
+
         logger.debug(
             "Started app with PyMS and this services: {}".format(self.services)
         )

pyms/flask/services/opentelemetry.py

@@ -0,0 +1,133 @@
+import logging
+import time
+from typing import Text
+
+from flask import Blueprint, Response, request
+from pyms.flask.services.driver import DriverService
+
+from opentelemetry import metrics
+from opentelemetry.exporter.prometheus import PrometheusMetricsExporter
+from opentelemetry.sdk.metrics import Counter, MeterProvider, ValueRecorder
+from opentelemetry.sdk.metrics.export.controller import PushController
+from prometheus_client import generate_latest
+
+# TODO set sane defaults
+# https://github.com/python-microservices/pyms/issues/218
+# TODO validate config
+# https://github.com/python-microservices/pyms/issues/219
+PROMETHEUS_CLIENT = "prometheus"
+
+
+class FlaskMetricsWrapper:
+    def __init__(self, app_name: str, meter: MeterProvider):
+        self.app_name = app_name
+        # TODO add Histogram support for flask when available
+        # https://github.com/open-telemetry/opentelemetry-python/issues/1255
+        self.flask_request_latency = meter.create_metric(
+            "http_server_requests_seconds",
+            "Flask Request Latency",
+            "http_server_requests_seconds",
+            float,
+            ValueRecorder,
+            ("service", "method", "uri", "status"),
+        )
+        self.flask_request_count = meter.create_metric(
+            "http_server_requests_count",
+            "Flask Request Count",
+            "http_server_requests_count",
+            int,
+            Counter,
+            ["service", "method", "uri", "status"],
+        )
+
+    def before_request(self):  # pylint: disable=R0201
+        request.start_time = time.time()
+
+    def after_request(self, response: Response) -> Response:
+        if hasattr(request.url_rule, "rule"):
+            path = request.url_rule.rule
+        else:
+            path = request.path
+        request_latency = time.time() - request.start_time
+        labels = {
+            "service": self.app_name,
+            "method": str(request.method),
+            "uri": path,
+            "status": str(response.status_code),
+        }
+
+        self.flask_request_latency.record(request_latency, labels)
+        self.flask_request_count.add(1, labels)
+
+        return response
+
+
+class Service(DriverService):
+    """
+    Adds [OpenTelemetry](https://opentelemetry.io/) metrics using the [Opentelemetry Client Library](https://opentelemetry-python.readthedocs.io/en/latest/exporter/).
+    """
+
+    config_resource: Text = "opentelemetry"
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.blueprint = Blueprint("opentelemetry", __name__)
+        self.serve_metrics()
+
+    def set_metrics_backend(self):
+        # Set meter provider
+        metrics.set_meter_provider(MeterProvider())
+        self.meter = metrics.get_meter(__name__)
+        if self.config.metrics.backend.lower() == PROMETHEUS_CLIENT:
+            exporter = PrometheusMetricsExporter()
+        else:
+            pass
+        # Create the push controller that will update the metrics when the
+        # interval is met
+        PushController(self.meter, exporter, self.config.metrics.interval)
+
+    def set_tracing_backend(self):
+        pass
+
+    def set_logging_backend(self):
+        pass
+
+    def monitor(self, app_name, app):
+        metric = FlaskMetricsWrapper(app_name, self.meter)
+        app.before_request(metric.before_request)
+        app.after_request(metric.after_request)
+
+    def serve_metrics(self):
+        @self.blueprint.route("/metrics", methods=["GET"])
+        def metrics():  # pylint: disable=unused-variable
+            return Response(
+                generate_latest(),
+                mimetype="text/print()lain",
+                content_type="text/plain; charset=utf-8",
+            )
+
+    def add_logger_handler(
+        self, logger: logging.Logger, service_name: str
+    ) -> logging.Logger:
+        logger.addHandler(MetricsLogHandler(service_name, self.meter))
+        return logger
+
+
+class MetricsLogHandler(logging.Handler):
+    """A LogHandler that exports logging metrics for OpenTelemetry."""
+
+    def __init__(self, app_name: str, meter: MeterProvider):
+        super().__init__()
+        self.app_name = str(app_name)
+        self.logger_total_messages = meter.create_metric(
+            "logger_messages_total",
+            "Count of log entries by service and level.",
+            "logger_messages_total",
+            int,
+            Counter,
+            ["service", "level"],
+        )
+
+    def emit(self, record) -> None:
+        labels = {"service": self.app_name, "level": record.levelname}
+        self.logger_total_messages.add(1, labels)

setup.py

@@ -52,6 +52,11 @@
     'prometheus_client>=0.8.0',
 ]
 
+install_opentelemetry_requires = [
+    'opentelemetry-exporter-prometheus>=0.14b0',
+    'opentelemetry-sdk>=0.14b0',
+]
+
 install_tests_requires = [
     'requests-mock>=1.8.0',
     'coverage>=5.3',