Observability Libs

  • By Jon Seager
Channel Revision Published Runs on
latest/edge 38 03 May 2024
Ubuntu 20.04
juju deploy observability-libs --channel edge
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Platform:

charms.observability_libs.v0.juju_topology

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 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.

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.

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.

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",
)

class InvalidUUIDError

Description

Invalid UUID was provided. None

Methods

InvalidUUIDError. __init__( self , uuid: str )

class JujuTopology

JujuTopology is used for storing, generating and formatting juju topology information.

Description

DEPRECATED: This class is deprecated. Use pip install cosl and from cosl.juju_topology import JujuTopology instead.

Methods

JujuTopology. __init__( self , model: str , model_uuid: str , application: str , unit , charm_name )

Build a JujuTopology object.

Arguments

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

Description

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.

JujuTopology. is_valid_uuid( self , uuid )

Validate the supplied UUID against the Juju Model UUID pattern.

Arguments

uuid

string that needs to be checked if it is valid v4 UUID.

Returns

True if parameter is a valid v4 UUID, False otherwise.

JujuTopology. from_charm( cls , charm )

Creates a JujuTopology instance by using the model data available on a charm object.

Arguments

charm

a CharmBase object for which the JujuTopology will be constructed

Returns

a JujuTopology object.

JujuTopology. from_dict( cls , data: dict )

Factory method for creating JujuTopology children from a dictionary.

Arguments

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.

JujuTopology. as_dict( self )

Format the topology information into an ordered dict.

Arguments

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.

Description

Keeping the dictionary ordered is important to be able to compare dicts without having to resort to deep comparisons.

JujuTopology. identifier( self )

Format the topology information into a terse string.

Description

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'

JujuTopology. label_matcher_dict( self )

Format the topology information into a dict with keys having 'juju_' as prefix.

Description

Relabelled topology never includes the unit as it would then only match the leader unit (ie. the unit that produced the dict).

JujuTopology. label_matchers( self )

Format the topology information into a promql/logql label matcher string.

Description

Topology label matchers should never include the unit as it would then only match the leader unit (ie. the unit that produced the matchers).

JujuTopology. model( self )

Description

Getter for the juju model value. None

JujuTopology. model_uuid( self )

Description

Getter for the juju model uuid value. None

JujuTopology. model_uuid_short( self )

Description

Getter for the juju model value, truncated to the first eight letters. None

JujuTopology. application( self )

Description

Getter for the juju application value. None

JujuTopology. charm_name( self )

Description

Getter for the juju charm name value. None

JujuTopology. unit( self )

Description

Getter for the juju unit value. None