Loki

Overview.

This document explains how to use the two principal objects this library provides:

• LokiPushApiProvider: This object is meant to be used by any Charmed Operator that needs to

implement the provider side of the loki_push_api relation interface. For instance, a Loki charm. The provider side of the relation represents the server side, to which logs are being pushed.

• LokiPushApiConsumer: This object is meant to be used by any Charmed Operator that needs to

send log to Loki by implementing the consumer side of the loki_push_api relation interface. For instance, a Promtail or Grafana agent charm which needs to send logs to Loki.

• LogProxyConsumer: This object can be used by any Charmed Operator which needs to

send telemetry, such as logs, to Loki through a Log Proxy by implementing the consumer side of the loki_push_api relation interface.

Filtering logs in Loki is largely performed on the basis of labels. In the Juju ecosystem, Juju topology labels are used to uniquely identify the workload which generates telemetry like logs.

In order to be able to control the labels on the logs pushed this object adds a Pebble layer that runs Promtail in the workload container, injecting Juju topology labels into the logs on the fly.

LokiPushApiProvider Library Usage

This object may be used by any Charmed Operator which implements the loki_push_api interface. For instance, Loki or Grafana Agent.

For this purpose a charm needs to instantiate the LokiPushApiProvider object with one mandatory and three optional arguments.

• charm: A reference to the parent (Loki) charm.

• relation_name: The name of the relation that the charm uses to interact with its clients, which implement LokiPushApiConsumer or LogProxyConsumer.

  If provided, this relation name must match a provided relation in metadata.yaml with the loki_push_api interface.

  The default relation name is "logging" for LokiPushApiConsumer and "log-proxy" for LogProxyConsumer.

  For example, a provider's metadata.yaml file may look as follows:

  provides:
    logging:
      interface: loki_push_api
  

  Subsequently, a Loki charm may instantiate the LokiPushApiProvider in its constructor as follows:

  from charms.loki_k8s.v0.loki_push_api import LokiPushApiProvider
  from loki_server import LokiServer
  ...
  
  class LokiOperatorCharm(CharmBase):
      ...
  
      def __init__(self, *args):
          super().__init__(*args)
          ...
          external_url = urlparse(self._external_url)
          self.loki_provider = LokiPushApiProvider(
              self,
              address=external_url.hostname or self.hostname,
              port=external_url.port or 80,
              scheme=external_url.scheme,
              path=f"{external_url.path}/loki/api/v1/push",
          )
          ...
  
  

  • port: Loki Push Api endpoint port. Default value: 3100.
  • scheme: Loki Push Api endpoint scheme (HTTP or HTTPS). Default value: HTTP
  • address: Loki Push Api endpoint address. Default value: localhost
  • path: Loki Push Api endpoint path. Default value: loki/api/v1/push

The LokiPushApiProvider object has several responsibilities:

1. Set the URL of the Loki Push API in the relation application data bag; the URL must be unique to all instances (e.g. using a load balancer).

2. Set the Promtail binary URL (promtail_binary_zip_url) so clients that use LogProxyConsumer object could download and configure it.

3. Process the metadata of the consumer application, provided via the "metadata" field of the consumer data bag, which are used to annotate the alert rules (see next point). An example for "metadata" is the following:

   {'model': 'loki', 'model_uuid': '0b7d1071-ded2-4bf5-80a3-10a81aeb1386', 'application': 'promtail-k8s' }

4. Process alert rules set into the relation by the LokiPushApiConsumer objects, e.g.:

   '{ "groups": [{ "name": "loki_0b7d1071-ded2-4bf5-80a3-10a81aeb1386_promtail-k8s_alerts", "rules": [{ "alert": "HighPercentageError", "expr": "sum(rate({app=\"foo\", env=\"production\"} |= \"error\" [5m])) by (job) \n /\nsum(rate({app=\"foo\", env=\"production\"}[5m])) by (job)\n > 0.05 \n", "for": "10m", "labels": { "severity": "page", "juju_model": "loki", "juju_model_uuid": "0b7d1071-ded2-4bf5-80a3-10a81aeb1386", "juju_application": "promtail-k8s" }, "annotations": { "summary": "High request latency" } }] }] }'

Once these alert rules are sent over relation data, the LokiPushApiProvider object stores these files in the directory /loki/rules inside the Loki charm container. After storing alert rules files, the object will check alert rules by querying Loki API endpoint: loki/api/v1/rules. If there are changes in the alert rules a loki_push_api_alert_rules_changed event will be emitted with details about the RelationEvent which triggered it.

This events should be observed in the charm that uses LokiPushApiProvider:

    def __init__(self, *args):
        super().__init__(*args)
        ...
        self.loki_provider = LokiPushApiProvider(self)
        self.framework.observe(
            self.loki_provider.on.loki_push_api_alert_rules_changed,
            self._loki_push_api_alert_rules_changed,
        )

LokiPushApiConsumer Library Usage

This Loki charm interacts with its clients using the Loki charm library. Charms seeking to send log to Loki, must do so using the LokiPushApiConsumer object from this charm library.

NOTE: LokiPushApiConsumer also depends on an additional charm library.

Ensure sure you charmcraft fetch-lib charms.observability_libs.v0.juju_topology when using this library.

For the simplest use cases, using the LokiPushApiConsumer object only requires instantiating it, typically in the constructor of your charm (the one which sends logs).

from charms.loki_k8s.v0.loki_push_api import LokiPushApiConsumer

class LokiClientCharm(CharmBase):

    def __init__(self, *args):
        super().__init__(*args)
        ...
        self._loki_consumer = LokiPushApiConsumer(self)

The LokiPushApiConsumer constructor requires two things:

• A reference to the parent (LokiClientCharm) charm.

• Optionally, the name of the relation that the Loki charm uses to interact with its clients. If provided, this relation name must match a required relation in metadata.yaml with the loki_push_api interface.

  This argument is not required if your metadata.yaml has precisely one required relation in metadata.yaml with the loki_push_api interface, as the lib will automatically resolve the relation name inspecting the using the meta information of the charm

Any time the relation between a Loki provider charm and a Loki consumer charm is established, a LokiPushApiEndpointJoined event is fired. In the consumer side is it possible to observe this event with:

self.framework.observe(
    self._loki_consumer.on.loki_push_api_endpoint_joined,
    self._on_loki_push_api_endpoint_joined,
)

Any time there are departures in relations between the consumer charm and Loki the consumer charm is informed, through a LokiPushApiEndpointDeparted event, for instance:

self.framework.observe(
    self._loki_consumer.on.loki_push_api_endpoint_departed,
    self._on_loki_push_api_endpoint_departed,
)

The consumer charm can then choose to update its configuration in both situations.

Note that LokiPushApiConsumer does not add any labels automatically on its own. In order to better integrate with the Canonical Observability Stack, you may want to configure your software to add Juju topology labels. The observability-libs library can be used to get topology labels in charm code. See :func:LogProxyConsumer._scrape_configs for an example of how to do this with promtail.

LogProxyConsumer Library Usage

Let's say that we have a workload charm that produces logs, and we need to send those logs to a workload implementing the loki_push_api interface, such as Loki or Grafana Agent.

Adopting this object in a Charmed Operator consist of two steps:

1. Use the LogProxyConsumer class by instantiating it in the __init__ method of the charmed operator. There are two ways to get logs in to promtail. You can give it a list of files to read, or you can write to it using the syslog protocol.

   For example:

   from charms.loki_k8s.v0.loki_push_api import LogProxyConsumer
   
   ...
   
       def __init__(self, *args):
           ...
           self._log_proxy = LogProxyConsumer(
               charm=self, log_files=LOG_FILES, container_name=PEER, enable_syslog=True
           )
   
           self.framework.observe(
               self._log_proxy.on.promtail_digest_error,
               self._promtail_error,
           )
   
       def _promtail_error(self, event):
           logger.error(event.message)
           self.unit.status = BlockedStatus(event.message)
   

   Any time the relation between a provider charm and a LogProxy consumer charm is established, a LogProxyEndpointJoined event is fired. In the consumer side is it possible to observe this event with:

   
   self.framework.observe(
       self._log_proxy.on.log_proxy_endpoint_joined,
       self._on_log_proxy_endpoint_joined,
   )
   

   Any time there are departures in relations between the consumer charm and the provider the consumer charm is informed, through a LogProxyEndpointDeparted event, for instance:

   self.framework.observe(
       self._log_proxy.on.log_proxy_endpoint_departed,
       self._on_log_proxy_endpoint_departed,
   )
   

   The consumer charm can then choose to update its configuration in both situations.

   Note that:

   • LOG_FILES is a list containing the log files we want to send to Loki or

   Grafana Agent, for instance:

   LOG_FILES = [
       "/var/log/apache2/access.log",
       "/var/log/alternatives.log",
   ]
   

   • container_name is the name of the container in which the application is running. If in the Pod there is only one container, this argument can be omitted.

   • You can configure your syslog software using localhost as the address and the method LogProxyConsumer.syslog_port to get the port, or, alternatively, if you are using rsyslog you may use the method LogProxyConsumer.rsyslog_config().

2. Modify the metadata.yaml file to add:

   • The log-proxy relation in the requires section:

     requires:
       log-proxy:
         interface: loki_push_api
         optional: true
     

Once the library is implemented in a Charmed Operator and a relation is established with the charm that implements the loki_push_api interface, the library will inject a Pebble layer that runs Promtail in the workload container to send logs.

By default, the promtail binary injected into the container will be downloaded from the internet. If, for any reason, the container has limited network access, you may allow charm administrators to provide their own promtail binary at runtime by adding the following snippet to your charm metadata:

resources:
  promtail-bin:
      type: file
      description: Promtail binary for logging
      filename: promtail-linux

Which would then allow operators to deploy the charm this way:

juju deploy \
    ./your_charm.charm \
    --resource promtail-bin=/tmp/promtail-linux-amd64

If a different resource name is used, it can be specified with the promtail_resource_name argument to the LogProxyConsumer constructor.

The object can emit a PromtailDigestError event:

• Promtail binary cannot be downloaded.
• The sha256 sum mismatch for promtail binary.

The object can raise a ContainerNotFoundError event:

• No container_name parameter has been specified and the Pod has more than 1 container.

These can be monitored via the PromtailDigestError events via:

   self.framework.observe(
       self._loki_consumer.on.promtail_digest_error,
       self._promtail_error,
   )

   def _promtail_error(self, event):
       logger.error(msg)
       self.unit.status = BlockedStatus(event.message)
    )

Alerting Rules

This charm library also supports gathering alerting rules from all related Loki client charms and enabling corresponding alerts within the Loki charm. Alert rules are automatically gathered by LokiPushApiConsumer object from a directory conventionally named loki_alert_rules.

This directory must reside at the top level in the src folder of the consumer charm. Each file in this directory is assumed to be a single alert rule in YAML format. The file name must have the .rule extension. The format of this alert rule conforms to the Loki docs.

An example of the contents of one such file is shown below.

alert: HighPercentageError
expr: |
  sum(rate({%%juju_topology%%} |= "error" [5m])) by (job)
    /
  sum(rate({%%juju_topology%%}[5m])) by (job)
    > 0.05
for: 10m
labels:
    severity: page
annotations:
    summary: High request latency

It is critical to use the %%juju_topology%% filter in the expression for the alert rule shown above. This filter is a stub that is automatically replaced by the LokiPushApiConsumer following Loki Client's Juju topology (application, model and its UUID). Such a topology filter is essential to ensure that alert rules submitted by one provider charm generates alerts only for that same charm.

The Loki charm may be related to multiple Loki client charms. Without this, filter rules submitted by one provider charm will also result in corresponding alerts for other provider charms. Hence, every alert rule expression must include such a topology filter stub.

Gathering alert rules and generating rule files within the Loki charm is easily done using the alerts() method of LokiPushApiProvider. Alerts generated by Loki will automatically include Juju topology labels in the alerts. These labels indicate the source of the alert.

The following labels are automatically added to every alert

• juju_model
• juju_model_uuid
• juju_application

Whether alert rules files does not contain the keys alert or expr or there is no alert rules file in alert_rules_path a loki_push_api_alert_rules_error event is emitted.

To handle these situations the event must be observed in the LokiClientCharm charm.py file:

class LokiClientCharm(CharmBase):

    def __init__(self, *args):
        super().__init__(*args)
        ...
        self._loki_consumer = LokiPushApiConsumer(self)

        self.framework.observe(
            self._loki_consumer.on.loki_push_api_alert_rules_error,
            self._alert_rules_error
        )

    def _alert_rules_error(self, event):
        self.unit.status = BlockedStatus(event.message)

Relation Data

The Loki charm uses both application and unit relation data to obtain information regarding Loki Push API and alert rules.

Units of consumer charm send their alert rules over app relation data using the alert_rules key.