Merge pull request #142 from canonical/cos_metrics_endpt

prometheus metrics endpoint charm

server/charm/Makefile

@@ -4,3 +4,5 @@ build: fetch-libs
 fetch-libs:
 	 charmcraft fetch-lib charms.data_platform_libs.v0.data_interfaces
 	 charmcraft fetch-lib charms.nginx_ingress_integrator.v0.nginx_route
+	 charmcraft fetch-lib charms.prometheus_k8s.v0.prometheus_scrape
+	 charmcraft fetch-lib charms.observability_libs.v0.juju_topology

server/charm/lib/charms/observability_libs/v0/juju_topology.py

@@ -0,0 +1,301 @@
+# Copyright 2022 Canonical Ltd.
+# See LICENSE file for licensing details.
+"""## Overview.
+
+This document explains how to use the `JujuTopology` class to
+create and consume topology information from Juju in a consistent manner.
+
+The goal of the Juju topology is to uniquely identify a piece
+of software running across any of your Juju-managed deployments.
+This is achieved by combining the following four elements:
+
+- Model name
+- Model UUID
+- Application name
+- Unit identifier
+
+
+For a more in-depth description of the concept, as well as a
+walk-through of it's use-case in observability, see
+[this blog post](https://juju.is/blog/model-driven-observability-part-2-juju-topology-metrics)
+on the Juju blog.
+
+## Library Usage
+
+This library may be used to create and consume `JujuTopology` objects.
+The `JujuTopology` class provides three ways to create instances:
+
+### Using the `from_charm` method
+
+Enables instantiation by supplying the charm as an argument. When
+creating topology objects for the current charm, this is the recommended
+approach.
+
+```python
+topology = JujuTopology.from_charm(self)
+```
+
+### Using the `from_dict` method
+
+Allows for instantion using a dictionary of relation data, like the
+`scrape_metadata` from Prometheus or the labels of an alert rule. When
+creating topology objects for remote charms, this is the recommended
+approach.
+
+```python
+scrape_metadata = json.loads(relation.data[relation.app].get("scrape_metadata", "{}"))
+topology = JujuTopology.from_dict(scrape_metadata)
+```
+
+### Using the class constructor
+
+Enables instantiation using whatever values you want. While this
+is useful in some very specific cases, this is almost certainly not
+what you are looking for as setting these values manually may
+result in observability metrics which do not uniquely identify a
+charm in order to provide accurate usage reporting, alerting,
+horizontal scaling, or other use cases.
+
+```python
+topology = JujuTopology(
+    model="some-juju-model",
+    model_uuid="00000000-0000-0000-0000-000000000001",
+    application="fancy-juju-application",
+    unit="fancy-juju-application/0",
+    charm_name="fancy-juju-application-k8s",
+)
+```
+
+"""
+from collections import OrderedDict
+from typing import Dict, List, Optional
+from uuid import UUID
+
+# The unique Charmhub library identifier, never change it
+LIBID = "bced1658f20f49d28b88f61f83c2d232"
+
+LIBAPI = 0
+LIBPATCH = 6
+
+
+class InvalidUUIDError(Exception):
+    """Invalid UUID was provided."""
+
+    def __init__(self, uuid: str):
+        self.message = "'{}' is not a valid UUID.".format(uuid)
+        super().__init__(self.message)
+
+
+class JujuTopology:
+    """JujuTopology is used for storing, generating and formatting juju topology information.
+
+    DEPRECATED: This class is deprecated. Use `pip install cosl` and
+    `from cosl.juju_topology import JujuTopology` instead.
+    """
+
+    def __init__(
+        self,
+        model: str,
+        model_uuid: str,
+        application: str,
+        unit: Optional[str] = None,
+        charm_name: Optional[str] = None,
+    ):
+        """Build a JujuTopology object.
+
+        A `JujuTopology` object is used for storing and transforming
+        Juju topology information. This information is used to
+        annotate Prometheus scrape jobs and alert rules. Such
+        annotation when applied to scrape jobs helps in identifying
+        the source of the scrapped metrics. On the other hand when
+        applied to alert rules topology information ensures that
+        evaluation of alert expressions is restricted to the source
+        (charm) from which the alert rules were obtained.
+
+        Args:
+            model: a string name of the Juju model
+            model_uuid: a globally unique string identifier for the Juju model
+            application: an application name as a string
+            unit: a unit name as a string
+            charm_name: name of charm as a string
+        """
+        if not self.is_valid_uuid(model_uuid):
+            raise InvalidUUIDError(model_uuid)
+
+        self._model = model
+        self._model_uuid = model_uuid
+        self._application = application
+        self._charm_name = charm_name
+        self._unit = unit
+
+    def is_valid_uuid(self, uuid):
+        """Validate the supplied UUID against the Juju Model UUID pattern.
+
+        Args:
+            uuid: string that needs to be checked if it is valid v4 UUID.
+
+        Returns:
+            True if parameter is a valid v4 UUID, False otherwise.
+        """
+        try:
+            return str(UUID(uuid, version=4)) == uuid
+        except (ValueError, TypeError):
+            return False
+
+    @classmethod
+    def from_charm(cls, charm):
+        """Creates a JujuTopology instance by using the model data available on a charm object.
+
+        Args:
+            charm: a `CharmBase` object for which the `JujuTopology` will be constructed
+        Returns:
+            a `JujuTopology` object.
+        """
+        return cls(
+            model=charm.model.name,
+            model_uuid=charm.model.uuid,
+            application=charm.model.app.name,
+            unit=charm.model.unit.name,
+            charm_name=charm.meta.name,
+        )
+
+    @classmethod
+    def from_dict(cls, data: dict):
+        """Factory method for creating `JujuTopology` children from a dictionary.
+
+        Args:
+            data: a dictionary with five keys providing topology information. The keys are
+                - "model"
+                - "model_uuid"
+                - "application"
+                - "unit"
+                - "charm_name"
+                `unit` and `charm_name` may be empty, but will result in more limited
+                labels. However, this allows us to support charms without workloads.
+
+        Returns:
+            a `JujuTopology` object.
+        """
+        return cls(
+            model=data["model"],
+            model_uuid=data["model_uuid"],
+            application=data["application"],
+            unit=data.get("unit", ""),
+            charm_name=data.get("charm_name", ""),
+        )
+
+    def as_dict(
+        self,
+        *,
+        remapped_keys: Optional[Dict[str, str]] = None,
+        excluded_keys: Optional[List[str]] = None,
+    ) -> OrderedDict:
+        """Format the topology information into an ordered dict.
+
+        Keeping the dictionary ordered is important to be able to
+        compare dicts without having to resort to deep comparisons.
+
+        Args:
+            remapped_keys: A dictionary mapping old key names to new key names,
+                which will be substituted when invoked.
+            excluded_keys: A list of key names to exclude from the returned dict.
+            uuid_length: The length to crop the UUID to.
+        """
+        ret = OrderedDict(
+            [
+                ("model", self.model),
+                ("model_uuid", self.model_uuid),
+                ("application", self.application),
+                ("unit", self.unit),
+                ("charm_name", self.charm_name),
+            ]
+        )
+        if excluded_keys:
+            ret = OrderedDict({k: v for k, v in ret.items() if k not in excluded_keys})
+
+        if remapped_keys:
+            ret = OrderedDict(
+                (remapped_keys.get(k), v) if remapped_keys.get(k) else (k, v) for k, v in ret.items()  # type: ignore
+            )
+
+        return ret
+
+    @property
+    def identifier(self) -> str:
+        """Format the topology information into a terse string.
+
+        This crops the model UUID, making it unsuitable for comparisons against
+        anything but other identifiers. Mainly to be used as a display name or file
+        name where long strings might become an issue.
+
+        >>> JujuTopology( \
+              model = "a-model", \
+              model_uuid = "00000000-0000-4000-8000-000000000000", \
+              application = "some-app", \
+              unit = "some-app/1" \
+            ).identifier
+        'a-model_00000000_some-app'
+        """
+        parts = self.as_dict(
+            excluded_keys=["unit", "charm_name"],
+        )
+
+        parts["model_uuid"] = self.model_uuid_short
+        values = parts.values()
+
+        return "_".join([str(val) for val in values]).replace("/", "_")
+
+    @property
+    def label_matcher_dict(self) -> Dict[str, str]:
+        """Format the topology information into a dict with keys having 'juju_' as prefix.
+
+        Relabelled topology never includes the unit as it would then only match
+        the leader unit (ie. the unit that produced the dict).
+        """
+        items = self.as_dict(
+            remapped_keys={"charm_name": "charm"},
+            excluded_keys=["unit"],
+        ).items()
+
+        return {"juju_{}".format(key): value for key, value in items if value}
+
+    @property
+    def label_matchers(self) -> str:
+        """Format the topology information into a promql/logql label matcher string.
+
+        Topology label matchers should never include the unit as it
+        would then only match the leader unit (ie. the unit that
+        produced the matchers).
+        """
+        items = self.label_matcher_dict.items()
+        return ", ".join(['{}="{}"'.format(key, value) for key, value in items if value])
+
+    @property
+    def model(self) -> str:
+        """Getter for the juju model value."""
+        return self._model
+
+    @property
+    def model_uuid(self) -> str:
+        """Getter for the juju model uuid value."""
+        return self._model_uuid
+
+    @property
+    def model_uuid_short(self) -> str:
+        """Getter for the juju model value, truncated to the first eight letters."""
+        return self._model_uuid[:8]
+
+    @property
+    def application(self) -> str:
+        """Getter for the juju application value."""
+        return self._application
+
+    @property
+    def charm_name(self) -> Optional[str]:
+        """Getter for the juju charm name value."""
+        return self._charm_name
+
+    @property
+    def unit(self) -> Optional[str]:
+        """Getter for the juju unit value."""
+        return self._unit