[DPE-4619] Add support for tracing through tempo-k8s (#296)

* Add support for tracing through tempo-k8s

* Update outdated charm lib

* Update charm tracing lib to v1.7

* Update charm_tracing lib + skip tracing when running unit tests

metadata.yaml

@@ -61,6 +61,10 @@ requires:
     interface: loki_push_api
     limit: 1
     optional: true
+  tracing:
+    interface: tracing
+    limit: 1
+    optional: true
 
 peers:
   pgb-peers:

pyproject.toml

@@ -35,6 +35,8 @@ poetry-core = "*"
 pydantic = "^1.10, <2"
 # grafana_agent/v0/cos_agent.py
 cosl = "*"
+# tempo_k8s/v1/charm_tracing.py
+opentelemetry-exporter-otlp-proto-http = "1.21.0"
 
 [tool.poetry.group.format]
 optional = true

src/charm.py

@@ -18,6 +18,8 @@
 from charms.loki_k8s.v0.loki_push_api import LogProxyConsumer
 from charms.postgresql_k8s.v0.postgresql_tls import PostgreSQLTLS
 from charms.prometheus_k8s.v0.prometheus_scrape import MetricsEndpointProvider
+from charms.tempo_k8s.v1.charm_tracing import trace_charm
+from charms.tempo_k8s.v2.tracing import TracingEndpointRequirer
 from jinja2 import Template
 from ops import JujuVersion
 from ops.charm import CharmBase, ConfigChangedEvent, PebbleReadyEvent
@@ -48,6 +50,8 @@
     TLS_CA_FILE,
     TLS_CERT_FILE,
     TLS_KEY_FILE,
+    TRACING_PROTOCOL,
+    TRACING_RELATION_NAME,
     UNIT_SCOPE,
 )
 from relations.backend_database import BackendDatabaseRequires
@@ -61,6 +65,19 @@
 Scopes = Literal[APP_SCOPE, UNIT_SCOPE]
 
 
+@trace_charm(
+    tracing_endpoint="tracing_endpoint",
+    extra_types=(
+        BackendDatabaseRequires,
+        DbProvides,
+        GrafanaDashboardProvider,
+        LogProxyConsumer,
+        MetricsEndpointProvider,
+        Peers,
+        PgBouncerProvider,
+        PgbouncerUpgrade,
+    ),
+)
 class PgBouncerK8sCharm(CharmBase):
     """A class implementing charmed PgBouncer."""
 
@@ -125,6 +142,15 @@ def __init__(self, *args):
             relation_name="upgrade",
             substrate="k8s",
         )
+        self.tracing = TracingEndpointRequirer(
+            self, relation_name=TRACING_RELATION_NAME, protocols=[TRACING_PROTOCOL]
+        )
+
+    @property
+    def tracing_endpoint(self) -> Optional[str]:
+        """Otlp http endpoint for charm instrumentation."""
+        if self.tracing.is_ready():
+            return self.tracing.get_endpoint(TRACING_PROTOCOL)
 
     @property
     def _node_name(self) -> str:

src/constants.py

@@ -42,3 +42,6 @@
     "monitoring_password": "monitoring-password",
     "auth_file": "auth-file",
 }
+
+TRACING_RELATION_NAME = "tracing"
+TRACING_PROTOCOL = "otlp_http"

tests/unit/conftest.py

@@ -0,0 +1,11 @@
+# Copyright 2023 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+import pytest
+from charms.tempo_k8s.v1.charm_tracing import charm_tracing_disabled
+
+
+@pytest.fixture(autouse=True)
+def disable_charm_tracing():
+    with charm_tracing_disabled():
+        yield