Merge ~spencerrunde/landscape-charm:cos-integration into landscape-charm:main

[Spencer Runde]

add basic COS integration

Add Grafana Agent library for basic level of integration. Currently supports logging through Loki. Creates symlinks for log files to work around limited support for log scraping in COS. Creates `/var/log/landscape-server` directory and sets permissions to syslog:landscape to work around a bug in which

Manual Testing:

Set up COS and Landscape Server:

1. Checkout branch
2. `cd landscape-charm` (if not already there)
3. `make build`
4. `juju deploy grafana-agent --channel edge`
5. `juju relate grafana-agent landscape-server`
6. Set up COS-Lite according to this guide: https://charmhub.io/prometheus-k8s/docs/deploy-cos-lite?channel=edge#heading--deploy-the-cos-lite-bundle
7. Follow Step 4 of the Grafana Machine Charm integration guide: https://charmhub.io/topics/canonical-observability-stack/tutorials/instrumenting-machine-charms#step-4-relate-grafana-agent-to-cos-lite-prometheus-loki-and-grafana
8. Navigate to Grafana dashboard - identify it using the COS-Lite guide again: https://charmhub.io/prometheus-k8s/docs/deploy-cos-lite?channel=edge#heading--browse-dashboards

Verify Logs:

1. Try retrieving logs in the dashboard by navigating to "Explore" (the compass in the left sidebar).
2. Select the Loki instance from the dropdown in the upper left
3. Use the "code" mode of the query constructor. Construct a query like {juju_application="landscape-server", filename="/var/log/landscape-server-appserver.log"} and confirm that service logs (appserver, message-system, pingserver, etc.) are being logged. May also check that syslog logs appear. Grafana should hint filenames that have appeared so you don't have to sift through too much.

[Mitch Burton (mitchburton)]

Not the world's best installation experience, but I think it'll do for now/MVP. Tested it out on a microk8s cloud (after fighting for awhile with the setup there).

+1 LGTM with 1 minor inline comment.

review: Approve

bbdc76a... by Spencer Runde on 2023-10-31

add basic COS integration

diff --git a/lib/charms/grafana_agent/v0/cos_agent.py b/lib/charms/grafana_agent/v0/cos_agent.py
new file mode 100644
index 0000000..d3130b2
--- /dev/null
+++ b/lib/charms/grafana_agent/v0/cos_agent.py
@@ -0,0 +1,842 @@
+# Copyright 2023 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+r"""## Overview.
+
+This library can be used to manage the cos_agent relation interface:
+
+- `COSAgentProvider`: Use in machine charms that need to have a workload's metrics
+  or logs scraped, or forward rule files or dashboards to Prometheus, Loki or Grafana through
+  the Grafana Agent machine charm.
+
+- `COSAgentConsumer`: Used in the Grafana Agent machine charm to manage the requirer side of
+  the `cos_agent` interface.
+
+
+## COSAgentProvider Library Usage
+
+Grafana Agent machine Charmed Operator interacts with its clients using the cos_agent library.
+Charms seeking to send telemetry, must do so using the `COSAgentProvider` object from
+this charm library.
+
+Using the `COSAgentProvider` object only requires instantiating it,
+typically in the `__init__` method of your charm (the one which sends telemetry).
+
+The constructor of `COSAgentProvider` has only one required and nine optional parameters:
+
+```python
+    def __init__(
+        self,
+        charm: CharmType,
+        relation_name: str = DEFAULT_RELATION_NAME,
+        metrics_endpoints: Optional[List[_MetricsEndpointDict]] = None,
+        metrics_rules_dir: str = "./src/prometheus_alert_rules",
+        logs_rules_dir: str = "./src/loki_alert_rules",
+        recurse_rules_dirs: bool = False,
+        log_slots: Optional[List[str]] = None,
+        dashboard_dirs: Optional[List[str]] = None,
+        refresh_events: Optional[List] = None,
+        scrape_configs: Optional[Union[List[Dict], Callable]] = None,
+    ):
+```
+
+### Parameters
+
+- `charm`: The instance of the charm that instantiates `COSAgentProvider`, typically `self`.
+
+- `relation_name`: If your charmed operator uses a relation name other than `cos-agent` to use
+    the `cos_agent` interface, this is where you have to specify that.
+
+- `metrics_endpoints`: In this parameter you can specify the metrics endpoints that Grafana Agent
+    machine Charmed Operator will scrape. The configs of this list will be merged with the configs
+    from `scrape_configs`.
+
+- `metrics_rules_dir`: The directory in which the Charmed Operator stores its metrics alert rules
+  files.
+
+- `logs_rules_dir`: The directory in which the Charmed Operator stores its logs alert rules files.
+
+- `recurse_rules_dirs`: This parameters set whether Grafana Agent machine Charmed Operator has to
+  search alert rules files recursively in the previous two directories or not.
+
+- `log_slots`: Snap slots to connect to for scraping logs in the form ["snap-name:slot", ...].
+
+- `dashboard_dirs`: List of directories where the dashboards are stored in the Charmed Operator.
+
+- `refresh_events`: List of events on which to refresh relation data.
+
+- `scrape_configs`: List of standard scrape_configs dicts or a callable that returns the list in
+    case the configs need to be generated dynamically. The contents of this list will be merged
+    with the configs from `metrics_endpoints`.
+
+
+### Example 1 - Minimal instrumentation:
+
+In order to use this object the following should be in the `charm.py` file.
+
+```python
+from charms.grafana_agent.v0.cos_agent import COSAgentProvider
+...
+class TelemetryProviderCharm(CharmBase):
+    def __init__(self, *args):
+        ...
+        self._grafana_agent = COSAgentProvider(self)
+```
+
+### Example 2 - Full instrumentation:
+
+In order to use this object the following should be in the `charm.py` file.
+
+```python
+from charms.grafana_agent.v0.cos_agent import COSAgentProvider
+...
+class TelemetryProviderCharm(CharmBase):
+    def __init__(self, *args):
+        ...
+        self._grafana_agent = COSAgentProvider(
+            self,
+            relation_name="custom-cos-agent",
+            metrics_endpoints=[
+                # specify "path" and "port" to scrape from localhost
+                {"path": "/metrics", "port": 9000},
+                {"path": "/metrics", "port": 9001},
+                {"path": "/metrics", "port": 9002},
+            ],
+            metrics_rules_dir="./src/alert_rules/prometheus",
+            logs_rules_dir="./src/alert_rules/loki",
+            recursive_rules_dir=True,
+            log_slots=["my-app:slot"],
+            dashboard_dirs=["./src/dashboards_1", "./src/dashboards_2"],
+            refresh_events=["update-status", "upgrade-charm"],
+            scrape_configs=[
+                {
+                    "job_name": "custom_job",
+                    "metrics_path": "/metrics",
+                    "authorization": {"credentials": "bearer-token"},
+                    "static_configs": [
+                        {
+                            "targets": ["localhost:9003"]},
+                            "labels": {"key": "value"},
+                        },
+                    ],
+                },
+            ]
+        )
+```
+
+### Example 3 - Dynamic scrape configs generation:
+
+Pass a function to the `scrape_configs` to decouple the generation of the configs
+from the instantiation of the COSAgentProvider object.
+
+```python
+from charms.grafana_agent.v0.cos_agent import COSAgentProvider
+...
+
+class TelemetryProviderCharm(CharmBase):
+    def generate_scrape_configs(self):
+        return [
+            {
+                "job_name": "custom",
+                "metrics_path": "/metrics",
+                "static_configs": [{"targets": ["localhost:9000"]}],
+            },
+        ]
+
+    def __init__(self, *args):
+        ...
+        self._grafana_agent = COSAgentProvider(
+            self,
+            scrape_configs=self.generate_scrape_configs,
+        )
+```
+
+## COSAgentConsumer Library Usage
+
+This object may be used by any Charmed Operator which gathers telemetry data by
+implementing the consumer side of the `cos_agent` interface.
+For instance Grafana Agent machine Charmed Operator.
+
+For this purpose the charm needs to instantiate the `COSAgentConsumer` object with one mandatory
+and two optional arguments.
+
+### Parameters
+
+- `charm`: A reference to the parent (Grafana Agent machine) charm.
+
+- `relation_name`: The name of the relation that the charm uses to interact
+  with its clients that provides telemetry data using the `COSAgentProvider` object.
+
+  If provided, this relation name must match a provided relation in metadata.yaml with the
+  `cos_agent` interface.
+  The default value of this argument is "cos-agent".
+
+- `refresh_events`: List of events on which to refresh relation data.
+
+
+### Example 1 - Minimal instrumentation:
+
+In order to use this object the following should be in the `charm.py` file.
+
+```python
+from charms.grafana_agent.v0.cos_agent import COSAgentConsumer
+...
+class GrafanaAgentMachineCharm(GrafanaAgentCharm)
+    def __init__(self, *args):
+        ...
+        self._cos = COSAgentRequirer(self)
+```
+
+
+### Example 2 - Full instrumentation:
+
+In order to use this object the following should be in the `charm.py` file.
+
+```python
+from charms.grafana_agent.v0.cos_agent import COSAgentConsumer
+...
+class GrafanaAgentMachineCharm(GrafanaAgentCharm)
+    def __init__(self, *args):
+        ...
+        self._cos = COSAgentRequirer(
+            self,
+            relation_name="cos-agent-consumer",
+            refresh_events=["update-status", "upgrade-charm"],
+        )
+```
+"""
+
+import base64
+import json
+import logging
+import lzma
+from collections import namedtuple
+from itertools import chain
+from pathlib import Path
+from typing import TYPE_CHECKING, Any, Callable, ClassVar, Dict, List, Optional, Set, Union
+
+import pydantic
+from cosl import JujuTopology
+from cosl.rules import AlertRules
+from ops.charm import RelationChangedEvent
+from ops.framework import EventBase, EventSource, Object, ObjectEvents
+from ops.model import Relation, Unit
+from ops.testing import CharmType
+
+if TYPE_CHECKING:
+    try:
+        from typing import TypedDict
+
+        class _MetricsEndpointDict(TypedDict):
+            path: str
+            port: int
+
+    except ModuleNotFoundError:
+        _MetricsEndpointDict = Dict  # pyright: ignore
+
+LIBID = "dc15fa84cef84ce58155fb84f6c6213a"
+LIBAPI = 0
+LIBPATCH = 6
+
+PYDEPS = ["cosl", "pydantic < 2"]
+
+DEFAULT_RELATION_NAME = "cos-agent"
+DEFAULT_PEER_RELATION_NAME = "peers"
+DEFAULT_SCRAPE_CONFIG = {
+    "static_configs": [{"targets": ["localhost:80"]}],
+    "metrics_path": "/metrics",
+}
+
+logger = logging.getLogger(__name__)
+SnapEndpoint = namedtuple("SnapEndpoint", "owner, name")
+
+
+class GrafanaDashboard(str):
+    """Grafana Dashboard encoded json; lzma-compressed."""
+
+    # TODO Replace this with a custom type when pydantic v2 released (end of 2023 Q1?)
+    # https://github.com/pydantic/pydantic/issues/4887
+    @staticmethod
+    def _serialize(raw_json: Union[str, bytes]) -> "GrafanaDashboard":
+        if not isinstance(raw_json, bytes):
+            raw_json = raw_json.encode("utf-8")
+        encoded = base64.b64encode(lzma.compress(raw_json)).decode("utf-8")
+        return GrafanaDashboard(encoded)
+
+    def _deserialize(self) -> Dict:
+        try:
+            raw = lzma.decompress(base64.b64decode(self.encode("utf-8"))).decode()
+            return json.loads(raw)
+        except json.decoder.JSONDecodeError as e:
+            logger.error("Invalid Dashboard format: %s", e)
+            return {}
+
+    def __repr__(self):
+        """Return string representation of self."""
+        return "<GrafanaDashboard>"
+
+
+class CosAgentProviderUnitData(pydantic.BaseModel):
+    """Unit databag model for `cos-agent` relation."""
+
+    # The following entries are the same for all units of the same principal.
+    # Note that the same grafana agent subordinate may be related to several apps.
+    # this needs to make its way to the gagent leader
+    metrics_alert_rules: dict
+    log_alert_rules: dict
+    dashboards: List[GrafanaDashboard]
+    subordinate: Optional[bool]
+
+    # The following entries may vary across units of the same principal app.
+    # this data does not need to be forwarded to the gagent leader
+    metrics_scrape_jobs: List[Dict]
+    log_slots: List[str]
+
+    # when this whole datastructure is dumped into a databag, it will be nested under this key.
+    # while not strictly necessary (we could have it 'flattened out' into the databag),
+    # this simplifies working with the model.
+    KEY: ClassVar[str] = "config"
+
+
+class CosAgentPeersUnitData(pydantic.BaseModel):
+    """Unit databag model for `peers` cos-agent machine charm peer relation."""
+
+    # We need the principal unit name and relation metadata to be able to render identifiers
+    # (e.g. topology) on the leader side, after all the data moves into peer data (the grafana
+    # agent leader can only see its own principal, because it is a subordinate charm).
+    principal_unit_name: str
+    principal_relation_id: str
+    principal_relation_name: str
+
+    # The only data that is forwarded to the leader is data that needs to go into the app databags
+    # of the outgoing o11y relations.
+    metrics_alert_rules: Optional[dict]
+    log_alert_rules: Optional[dict]
+    dashboards: Optional[List[GrafanaDashboard]]
+
+    # when this whole datastructure is dumped into a databag, it will be nested under this key.
+    # while not strictly necessary (we could have it 'flattened out' into the databag),
+    # this simplifies working with the model.
+    KEY: ClassVar[str] = "config"
+
+    @property
+    def app_name(self) -> str:
+        """Parse out the app name from the unit name.
+
+        TODO: Switch to using `model_post_init` when pydantic v2 is released?
+          https://github.com/pydantic/pydantic/issues/1729#issuecomment-1300576214
+        """
+        return self.principal_unit_name.split("/")[0]
+
+
+class COSAgentProvider(Object):
+    """Integration endpoint wrapper for the provider side of the cos_agent interface."""
+
+    def __init__(
+        self,
+        charm: CharmType,
+        relation_name: str = DEFAULT_RELATION_NAME,
+        metrics_endpoints: Optional[List["_MetricsEndpointDict"]] = None,
+        metrics_rules_dir: str = "./src/prometheus_alert_rules",
+        logs_rules_dir: str = "./src/loki_alert_rules",
+        recurse_rules_dirs: bool = False,
+        log_slots: Optional[List[str]] = None,
+        dashboard_dirs: Optional[List[str]] = None,
+        refresh_events: Optional[List] = None,
+        *,
+        scrape_configs: Optional[Union[List[dict], Callable]] = None,
+    ):
+        """Create a COSAgentProvider instance.
+
+        Args:
+            charm: The `CharmBase` instance that is instantiating this object.
+            relation_name: The name of the relation to communicate over.
+            metrics_endpoints: List of endpoints in the form [{"path": path, "port": port}, ...].
+                This argument is a simplified form of the `scrape_configs`.
+                The contents of this list will be merged with the contents of `scrape_configs`.
+            metrics_rules_dir: Directory where the metrics rules are stored.
+            logs_rules_dir: Directory where the logs rules are stored.
+            recurse_rules_dirs: Whether to recurse into rule paths.
+            log_slots: Snap slots to connect to for scraping logs
+                in the form ["snap-name:slot", ...].
+            dashboard_dirs: Directory where the dashboards are stored.
+            refresh_events: List of events on which to refresh relation data.
+            scrape_configs: List of standard scrape_configs dicts or a callable
+                that returns the list in case the configs need to be generated dynamically.
+                The contents of this list will be merged with the contents of `metrics_endpoints`.
+        """
+        super().__init__(charm, relation_name)
+        dashboard_dirs = dashboard_dirs or ["./src/grafana_dashboards"]
+
+        self._charm = charm
+        self._relation_name = relation_name
+        self._metrics_endpoints = metrics_endpoints or []
+        self._scrape_configs = scrape_configs or []
+        self._metrics_rules = metrics_rules_dir
+        self._logs_rules = logs_rules_dir
+        self._recursive = recurse_rules_dirs
+        self._log_slots = log_slots or []
+        self._dashboard_dirs = dashboard_dirs
+        self._refresh_events = refresh_events or [self._charm.on.config_changed]
+
+        events = self._charm.on[relation_name]
+        self.framework.observe(events.relation_joined, self._on_refresh)
+        self.framework.observe(events.relation_changed, self._on_refresh)
+        for event in self._refresh_events:
+            self.framework.observe(event, self._on_refresh)
+
+    def _on_refresh(self, event):
+        """Trigger the class to update relation data."""
+        relations = self._charm.model.relations[self._relation_name]
+
+        for relation in relations:
+            # Before a principal is related to the grafana-agent subordinate, we'd get
+            # ModelError: ERROR cannot read relation settings: unit "zk/2": settings not found
+            # Add a guard to make sure it doesn't happen.
+            if relation.data and self._charm.unit in relation.data:
+                # Subordinate relations can communicate only over unit data.
+                try:
+                    data = CosAgentProviderUnitData(
+                        metrics_alert_rules=self._metrics_alert_rules,
+                        log_alert_rules=self._log_alert_rules,
+                        dashboards=self._dashboards,
+                        metrics_scrape_jobs=self._scrape_jobs,
+                        log_slots=self._log_slots,
+                        subordinate=self._charm.meta.subordinate,
+                    )
+                    relation.data[self._charm.unit][data.KEY] = data.json()
+                except (
+                    pydantic.ValidationError,
+                    json.decoder.JSONDecodeError,
+                ) as e:
+                    logger.error("Invalid relation data provided: %s", e)
+
+    @property
+    def _scrape_jobs(self) -> List[Dict]:
+        """Return a prometheus_scrape-like data structure for jobs.
+
+        https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config
+        """
+        if callable(self._scrape_configs):
+            scrape_configs = self._scrape_configs()
+        else:
+            # Create a copy of the user scrape_configs, since we will mutate this object
+            scrape_configs = self._scrape_configs.copy()
+
+        # Convert "metrics_endpoints" to standard scrape_configs, and add them in
+        for endpoint in self._metrics_endpoints:
+            scrape_configs.append(
+                {
+                    "metrics_path": endpoint["path"],
+                    "static_configs": [{"targets": [f"localhost:{endpoint['port']}"]}],
+                }
+            )
+
+        scrape_configs = scrape_configs or [DEFAULT_SCRAPE_CONFIG]
+
+        # Augment job name to include the app name and a unique id (index)
+        for idx, scrape_config in enumerate(scrape_configs):
+            scrape_config["job_name"] = "_".join(
+                [self._charm.app.name, str(idx), scrape_config.get("job_name", "default")]
+            )
+
+        return scrape_configs
+
+    @property
+    def _metrics_alert_rules(self) -> Dict:
+        """Use (for now) the prometheus_scrape AlertRules to initialize this."""
+        alert_rules = AlertRules(
+            query_type="promql", topology=JujuTopology.from_charm(self._charm)
+        )
+        alert_rules.add_path(self._metrics_rules, recursive=self._recursive)
+        return alert_rules.as_dict()
+
+    @property
+    def _log_alert_rules(self) -> Dict:
+        """Use (for now) the loki_push_api AlertRules to initialize this."""
+        alert_rules = AlertRules(query_type="logql", topology=JujuTopology.from_charm(self._charm))
+        alert_rules.add_path(self._logs_rules, recursive=self._recursive)
+        return alert_rules.as_dict()
+
+    @property
+    def _dashboards(self) -> List[GrafanaDashboard]:
+        dashboards: List[GrafanaDashboard] = []
+        for d in self._dashboard_dirs:
+            for path in Path(d).glob("*"):
+                dashboard = GrafanaDashboard._serialize(path.read_bytes())
+                dashboards.append(dashboard)
+        return dashboards
+
+
+class COSAgentDataChanged(EventBase):
+    """Event emitted by `COSAgentRequirer` when relation data changes."""
+
+
+class COSAgentValidationError(EventBase):
+    """Event emitted by `COSAgentRequirer` when there is an error in the relation data."""
+
+    def __init__(self, handle, message: str = ""):
+        super().__init__(handle)
+        self.message = message
+
+    def snapshot(self) -> Dict:
+        """Save COSAgentValidationError source information."""
+        return {"message": self.message}
+
+    def restore(self, snapshot):
+        """Restore COSAgentValidationError source information."""
+        self.message = snapshot["message"]
+
+
+class COSAgentRequirerEvents(ObjectEvents):
+    """`COSAgentRequirer` events."""
+
+    data_changed = EventSource(COSAgentDataChanged)
+    validation_error = EventSource(COSAgentValidationError)
+
+
+class MultiplePrincipalsError(Exception):
+    """Custom exception for when there are multiple principal applications."""
+
+    pass
+
+
+class COSAgentRequirer(Object):
+    """Integration endpoint wrapper for the Requirer side of the cos_agent interface."""
+
+    on = COSAgentRequirerEvents()  # pyright: ignore
+
+    def __init__(
+        self,
+        charm: CharmType,
+        *,
+        relation_name: str = DEFAULT_RELATION_NAME,
+        peer_relation_name: str = DEFAULT_PEER_RELATION_NAME,
+        refresh_events: Optional[List[str]] = None,
+    ):
+        """Create a COSAgentRequirer instance.
+
+        Args:
+            charm: The `CharmBase` instance that is instantiating this object.
+            relation_name: The name of the relation to communicate over.
+            peer_relation_name: The name of the peer relation to communicate over.
+            refresh_events: List of events on which to refresh relation data.
+        """
+        super().__init__(charm, relation_name)
+        self._charm = charm
+        self._relation_name = relation_name
+        self._peer_relation_name = peer_relation_name
+        self._refresh_events = refresh_events or [self._charm.on.config_changed]
+
+        events = self._charm.on[relation_name]
+        self.framework.observe(
+            events.relation_joined, self._on_relation_data_changed
+        )  # TODO: do we need this?
+        self.framework.observe(events.relation_changed, self._on_relation_data_changed)
+        for event in self._refresh_events:
+            self.framework.observe(event, self.trigger_refresh)  # pyright: ignore
+
+        # Peer relation events
+        # A peer relation is needed as it is the only mechanism for exchanging data across
+        # subordinate units.
+        # self.framework.observe(
+        #     self.on[self._peer_relation_name].relation_joined, self._on_peer_relation_joined
+        # )
+        peer_events = self._charm.on[peer_relation_name]
+        self.framework.observe(peer_events.relation_changed, self._on_peer_relation_changed)
+
+    @property
+    def peer_relation(self) -> Optional["Relation"]:
+        """Helper function for obtaining the peer relation object.
+
+        Returns: peer relation object
+        (NOTE: would return None if called too early, e.g. during install).
+        """
+        return self.model.get_relation(self._peer_relation_name)
+
+    def _on_peer_relation_changed(self, _):
+        # Peer data is used for forwarding data from principal units to the grafana agent
+        # subordinate leader, for updating the app data of the outgoing o11y relations.
+        if self._charm.unit.is_leader():
+            self.on.data_changed.emit()  # pyright: ignore
+
+    def _on_relation_data_changed(self, event: RelationChangedEvent):
+        # Peer data is the only means of communication between subordinate units.
+        if not self.peer_relation:
+            event.defer()
+            return
+
+        cos_agent_relation = event.relation
+        if not event.unit or not cos_agent_relation.data.get(event.unit):
+            return
+        principal_unit = event.unit
+
+        # Coherence check
+        units = cos_agent_relation.units
+        if len(units) > 1:
+            # should never happen
+            raise ValueError(
+                f"unexpected error: subordinate relation {cos_agent_relation} "
+                f"should have exactly one unit"
+            )
+
+        if not (raw := cos_agent_relation.data[principal_unit].get(CosAgentProviderUnitData.KEY)):
+            return
+
+        if not (provider_data := self._validated_provider_data(raw)):
+            return
+
+        # Copy data from the principal relation to the peer relation, so the leader could
+        # follow up.
+        # Save the originating unit name, so it could be used for topology later on by the leader.
+        data = CosAgentPeersUnitData(  # peer relation databag model
+            principal_unit_name=event.unit.name,
+            principal_relation_id=str(event.relation.id),
+            principal_relation_name=event.relation.name,
+            metrics_alert_rules=provider_data.metrics_alert_rules,
+            log_alert_rules=provider_data.log_alert_rules,
+            dashboards=provider_data.dashboards,
+        )
+        self.peer_relation.data[self._charm.unit][
+            f"{CosAgentPeersUnitData.KEY}-{event.unit.name}"
+        ] = data.json()
+
+        # We can't easily tell if the data that was changed is limited to only the data
+        # that goes into peer relation (in which case, if this is not a leader unit, we wouldn't
+        # need to emit `on.data_changed`), so we're emitting `on.data_changed` either way.
+        self.on.data_changed.emit()  # pyright: ignore
+
+    def _validated_provider_data(self, raw) -> Optional[CosAgentProviderUnitData]:
+        try:
+            return CosAgentProviderUnitData(**json.loads(raw))
+        except (pydantic.ValidationError, json.decoder.JSONDecodeError) as e:
+            self.on.validation_error.emit(message=str(e))  # pyright: ignore
+            return None
+
+    def trigger_refresh(self, _):
+        """Trigger a refresh of relation data."""
+        # FIXME: Figure out what we should do here
+        self.on.data_changed.emit()  # pyright: ignore
+
+    @property
+    def _principal_unit(self) -> Optional[Unit]:
+        """Return the principal unit for a relation.
+
+        Assumes that the relation is of type subordinate.
+        Relies on the fact that, for subordinate relations, the only remote unit visible to
+        *this unit* is the principal unit that this unit is attached to.
+        """
+        if relations := self._principal_relations:
+            # Technically it's a list, but for subordinates there can only be one relation
+            principal_relation = next(iter(relations))
+            if units := principal_relation.units:
+                # Technically it's a list, but for subordinates there can only be one
+                return next(iter(units))
+
+        return None
+
+    @property
+    def _principal_relations(self):
+        relations = []
+        for relation in self._charm.model.relations[self._relation_name]:
+            if not json.loads(relation.data[next(iter(relation.units))]["config"]).get(
+                ["subordinate"], False
+            ):
+                relations.append(relation)
+        if len(relations) > 1:
+            logger.error(
+                "Multiple applications claiming to be principal. Update the cos-agent library in the client application charms."
+            )
+            raise MultiplePrincipalsError("Multiple principal applications.")
+        return relations
+
+    @property
+    def _remote_data(self) -> List[CosAgentProviderUnitData]:
+        """Return a list of remote data from each of the related units.
+
+        Assumes that the relation is of type subordinate.
+        Relies on the fact that, for subordinate relations, the only remote unit visible to
+        *this unit* is the principal unit that this unit is attached to.
+        """
+        all_data = []
+
+        for relation in self._charm.model.relations[self._relation_name]:
+            if not relation.units:
+                continue
+            unit = next(iter(relation.units))
+            if not (raw := relation.data[unit].get(CosAgentProviderUnitData.KEY)):
+                continue
+            if not (provider_data := self._validated_provider_data(raw)):
+                continue
+            all_data.append(provider_data)
+
+        return all_data
+
+    def _gather_peer_data(self) -> List[CosAgentPeersUnitData]:
+        """Collect data from the peers.
+
+        Returns a trimmed-down list of CosAgentPeersUnitData.
+        """
+        relation = self.peer_relation
+
+        # Ensure that whatever context we're running this in, we take the necessary precautions:
+        if not relation or not relation.data or not relation.app:
+            return []
+
+        # Iterate over all peer unit data and only collect every principal once.
+        peer_data: List[CosAgentPeersUnitData] = []
+        app_names: Set[str] = set()
+
+        for unit in chain((self._charm.unit,), relation.units):
+            if not relation.data.get(unit):
+                continue
+
+            for unit_name in relation.data.get(unit):  # pyright: ignore
+                if not unit_name.startswith(CosAgentPeersUnitData.KEY):
+                    continue
+                raw = relation.data[unit].get(unit_name)
+                if raw is None:
+                    continue
+                data = CosAgentPeersUnitData(**json.loads(raw))
+                # Have we already seen this principal app?
+                if (app_name := data.app_name) in app_names:
+                    continue
+                peer_data.append(data)
+                app_names.add(app_name)
+
+        return peer_data
+
+    @property
+    def metrics_alerts(self) -> Dict[str, Any]:
+        """Fetch metrics alerts."""
+        alert_rules = {}
+
+        seen_apps: List[str] = []
+        for data in self._gather_peer_data():
+            if rules := data.metrics_alert_rules:
+                app_name = data.app_name
+                if app_name in seen_apps:
+                    continue  # dedup!
+                seen_apps.append(app_name)
+                # This is only used for naming the file, so be as specific as we can be
+                identifier = JujuTopology(
+                    model=self._charm.model.name,
+                    model_uuid=self._charm.model.uuid,
+                    application=app_name,
+                    # For the topology unit, we could use `data.principal_unit_name`, but that unit
+                    # name may not be very stable: `_gather_peer_data` de-duplicates by app name so
+                    # the exact unit name that turns up first in the iterator may vary from time to
+                    # time. So using the grafana-agent unit name instead.
+                    unit=self._charm.unit.name,
+                ).identifier
+
+                alert_rules[identifier] = rules
+
+        return alert_rules
+
+    @property
+    def metrics_jobs(self) -> List[Dict]:
+        """Parse the relation data contents and extract the metrics jobs."""
+        scrape_jobs = []
+        for data in self._remote_data:
+            for job in data.metrics_scrape_jobs:
+                # In #220, relation schema changed from a simplified dict to the standard
+                # `scrape_configs`.
+                # This is to ensure backwards compatibility with Providers older than v0.5.
+                if "path" in job and "port" in job and "job_name" in job:
+                    job = {
+                        "job_name": job["job_name"],
+                        "metrics_path": job["path"],
+                        "static_configs": [{"targets": [f"localhost:{job['port']}"]}],
+                    }
+
+                scrape_jobs.append(job)
+
+        return scrape_jobs
+
+    @property
+    def snap_log_endpoints(self) -> List[SnapEndpoint]:
+        """Fetch logging endpoints exposed by related snaps."""
+        plugs = []
+        for data in self._remote_data:
+            targets = data.log_slots
+            if targets:
+                for target in targets:
+                    if target in plugs:
+                        logger.warning(
+                            f"plug {target} already listed. "
+                            "The same snap is being passed from multiple "
+                            "endpoints; this should not happen."
+                        )
+                    else:
+                        plugs.append(target)
+
+        endpoints = []
+        for plug in plugs:
+            if ":" not in plug:
+                logger.error(f"invalid plug definition received: {plug}. Ignoring...")
+            else:
+                endpoint = SnapEndpoint(*plug.split(":"))
+                endpoints.append(endpoint)
+        return endpoints
+
+    @property
+    def logs_alerts(self) -> Dict[str, Any]:
+        """Fetch log alerts."""
+        alert_rules = {}
+        seen_apps: List[str] = []
+
+        for data in self._gather_peer_data():
+            if rules := data.log_alert_rules:
+                # This is only used for naming the file, so be as specific as we can be
+                app_name = data.app_name
+                if app_name in seen_apps:
+                    continue  # dedup!
+                seen_apps.append(app_name)
+
+                identifier = JujuTopology(
+                    model=self._charm.model.name,
+                    model_uuid=self._charm.model.uuid,
+                    application=app_name,
+                    # For the topology unit, we could use `data.principal_unit_name`, but that unit
+                    # name may not be very stable: `_gather_peer_data` de-duplicates by app name so
+                    # the exact unit name that turns up first in the iterator may vary from time to
+                    # time. So using the grafana-agent unit name instead.
+                    unit=self._charm.unit.name,
+                ).identifier
+
+                alert_rules[identifier] = rules
+
+        return alert_rules
+
+    @property
+    def dashboards(self) -> List[Dict[str, str]]:
+        """Fetch dashboards as encoded content.
+
+        Dashboards are assumed not to vary across units of the same primary.
+        """
+        dashboards: List[Dict[str, Any]] = []
+
+        seen_apps: List[str] = []
+        for data in self._gather_peer_data():
+            app_name = data.app_name
+            if app_name in seen_apps:
+                continue  # dedup!
+            seen_apps.append(app_name)
+
+            for encoded_dashboard in data.dashboards or ():
+                content = GrafanaDashboard(encoded_dashboard)._deserialize()
+
+                title = content.get("title", "no_title")
+
+                dashboards.append(
+                    {
+                        "relation_id": data.principal_relation_id,
+                        # We have the remote charm name - use it for the identifier
+                        "charm": f"{data.principal_relation_name}-{app_name}",
+                        "content": content,
+                        "title": title,
+                    }
+                )
+
+        return dashboards
diff --git a/metadata.yaml b/metadata.yaml
index efc7563..61ddaad 100644
--- a/metadata.yaml
+++ b/metadata.yaml
@@ -31,6 +31,8 @@ provides:
   nrpe-external-master:
     interface: nrpe-external-master
     scope: container
+  cos-agent:
+    interface: cos_agent
 
 peers:
   replicas:
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 4f2a3f5..671f33c 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,3 +1,7 @@
 -r requirements.txt
 coverage
 flake8
+
+# Grafana Agent Library
+cosl
+pydantic < 2
diff --git a/src/charm.py b/src/charm.py
index c5f5c59..7819018 100755
--- a/src/charm.py
+++ b/src/charm.py
@@ -24,6 +24,7 @@ from charms.operator_libs_linux.v0 import apt
 from charms.operator_libs_linux.v0.apt import PackageError, PackageNotFoundError
 from charms.operator_libs_linux.v0.passwd import group_exists, user_exists
 from charms.operator_libs_linux.v0.systemd import service_reload
+from charms.grafana_agent.v0.cos_agent import COSAgentProvider
 
 from ops.charm import (
     ActionEvent,
@@ -100,6 +101,50 @@ OIDC_CONFIG_VALS = (
     "oidc_logout_url",
 )
 
+LOG_DIRECTORY = "/var/log/landscape-server"
+LOG_FILES = [
+    "api.log",
+    "appserver.log",
+    "async-frontend.log",
+    "job-handler.log",
+    "landscape-profiles.log",
+    "message-server.log",
+    "package-search.log",
+    "package-upload.log",
+    "pingserver.log",
+]
+
+
+def _create_logfile_symlinks(log_dir, log_files):
+    """Symlink /var/log/<application>/ logs to /var/log/ as <application>-<logfile>.log
+
+    Temporary method to support logging with COS.  COS is limited to scraping
+    logs directly under /var/log/
+    """
+    base_dir, prefix = os.path.split(log_dir)
+    for logfile in log_files:
+        src = os.path.join(log_dir, f"{logfile}")
+        dst = os.path.join(base_dir, f"{prefix}-{logfile}")
+        try:
+            os.symlink(src, dst)
+        except FileExistsError:
+            pass
+
+
+def _set_log_dir_permissions(log_dir):
+    """Set permissions on /var/log/landscape-server to drwxrwxr-x.
+
+    Set ownership to syslog:landscape.
+    """
+    try:
+        os.chmod(log_dir, 0o775)
+    except FileNotFoundError:
+        os.makedirs(log_dir)
+        os.chmod(log_dir, 0o775)
+        uid = 104  # syslog
+        gid = 116  # landscape
+        os.chown(log_dir, uid, gid)
+
 
 class LandscapeServerCharm(CharmBase):
     """Charm the service."""
@@ -178,6 +223,8 @@ class LandscapeServerCharm(CharmBase):
         self.landscape_uid = user_exists("landscape").pw_uid
         self.root_gid = group_exists("root").gr_gid
 
+        self._grafana_agent = COSAgentProvider(self)
+
     def _on_config_changed(self, _) -> None:
         prev_status = self.unit.status
 
@@ -297,6 +344,11 @@ class LandscapeServerCharm(CharmBase):
             self.unit.status = MaintenanceStatus("Installing SSL certificate")
             write_ssl_cert(config_ssl_cert)
 
+        _set_log_dir_permissions(LOG_DIRECTORY)
+
+        # For logging integration with COS
+        _create_logfile_symlinks(LOG_DIRECTORY, LOG_FILES)
+
         # Write the license file, if it exists.
         license_file = self.model.config.get("license_file")
 
diff --git a/tests/test_charm.py b/tests/test_charm.py
index 0b1477d..a4d2b2d 100644
--- a/tests/test_charm.py
+++ b/tests/test_charm.py
@@ -4,6 +4,7 @@
 # Learn more about testing at: https://juju.is/docs/sdk/testing
 
 import os
+import stat
 import unittest
 from grp import struct_group
 from io import BytesIO
@@ -24,7 +25,8 @@ from charms.operator_libs_linux.v0.apt import (
 
 from charm import (
     DEFAULT_SERVICES, HAPROXY_CONFIG_FILE, LANDSCAPE_PACKAGES, LEADER_SERVICES, LSCTL,
-    NRPE_D_DIR, SCHEMA_SCRIPT, HASH_ID_DATABASES, LandscapeServerCharm)
+    NRPE_D_DIR, SCHEMA_SCRIPT, HASH_ID_DATABASES, LandscapeServerCharm, _create_logfile_symlinks,
+    _set_log_dir_permissions)
 
 
 class TestCharm(unittest.TestCase):
@@ -65,6 +67,8 @@ class TestCharm(unittest.TestCase):
             apt=DEFAULT,
             prepend_default_settings=DEFAULT,
             update_service_conf=DEFAULT,
+            _create_logfile_symlinks=DEFAULT,
+            _set_log_dir_permissions=DEFAULT,
         )
         ppa = harness.model.config.get("landscape_ppa")
 
@@ -141,6 +145,8 @@ class TestCharm(unittest.TestCase):
             write_ssl_cert=DEFAULT,
             update_service_conf=DEFAULT,
             prepend_default_settings=DEFAULT,
+            _create_logfile_symlinks=DEFAULT,
+            _set_log_dir_permissions=DEFAULT,
         )
 
         peer_relation_id = harness.add_relation("replicas", "landscape-server")
@@ -170,6 +176,8 @@ class TestCharm(unittest.TestCase):
             write_license_file=DEFAULT,
             prepend_default_settings=DEFAULT,
             update_service_conf=DEFAULT,
+            _create_logfile_symlinks=DEFAULT,
+            _set_log_dir_permissions=DEFAULT,
         )
 
         with patches as mocks:
@@ -193,6 +201,8 @@ class TestCharm(unittest.TestCase):
                 update_service_conf=DEFAULT,
                 prepend_default_settings=DEFAULT,
                 write_license_file=DEFAULT,
+                _create_logfile_symlinks=DEFAULT,
+                _set_log_dir_permissions=DEFAULT,
         ) as mocks:
             harness.begin_with_initial_hooks()
 
@@ -1320,3 +1330,33 @@ class TestBootstrapAccount(unittest.TestCase):
             text=True
         )
         event.fail.assert_called_once()
+
+    def test_log_symlink_src_does_not_exist(self):
+        """Creating a symlink that points to a non-existent src doesn't raise an Exception"""
+        with TemporaryDirectory() as tmpdir:
+            log_dir = os.path.join(tmpdir, "var", "log", "landscape-server")
+            os.makedirs(log_dir)
+            log_files = ["test1.log", "test2.log", "test3.log"]
+            _create_logfile_symlinks(log_dir, log_files)
+
+    def test_log_symlink_already_exists(self):
+        """Creating symlinks that already exist doesn't raise an Exception"""
+        with TemporaryDirectory() as tmpdir:
+            log_dir = os.path.join(tmpdir, "var", "log", "landscape-server")
+            os.makedirs(log_dir)
+            file_names = ["test1.log", "test2.log", "test3.log"]
+            for file_name in file_names:
+                log_file = os.path.join(log_dir, file_name)
+                open(log_file, "wb").close()  # create empty files
+            _create_logfile_symlinks(log_dir, file_names)
+            _create_logfile_symlinks(log_dir, file_names)
+
+    def test_set_log_dir_permissions_dir_does_not_exist(self):
+        """Setting permissions on a non-existent log dir creates the dir and sets permissions"""
+        with TemporaryDirectory() as tmpdir:
+            with patch("os.chown") as _:  # chown to new user requires root
+                log_dir = os.path.join(tmpdir, "var", "log", "landscape-server")
+                _set_log_dir_permissions(log_dir)
+                self.assertTrue(os.path.exists(log_dir))
+                permissions = os.stat(log_dir).st_mode
+                self.assertTrue(0o755, oct(stat.S_IMODE(permissions)))  # 755 = drwxrwxr-x file perms
\ No newline at end of file