istio-k8s

Istio

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latest/edge 23 17 Apr 2025
Ubuntu 22.04
juju deploy istio-k8s --channel edge
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Platform:

Ubuntu
22.04

charms.istio_k8s.v0.istio_metadata

istio_metadata.

This library implements endpoint wrappers for the istio-metadata interface. The istio-metadata interface is used to transfer information about an instance of Istio, such as its root namespace. Typically, this is useful for charms that need details on how to interface with Istio.

Usage
Requirer

IstioMetadataRequirer is a wrapper for pulling data from the istio-metadata interface. To use it in your charm:

  • observe the relation-changed and relation-broken events for this relation wherever your charm needs to use this data (this endpoint wrapper DOES NOT automatically observe any events)
  • wherever you need access to the data, call IstioMetadataRequirer(...).get_data()

An example implementation is:

class FooCharm(CharmBase):
    def __init__(self, framework):
        super().__init__(framework)

        istio_metadata = IstioMetadataRequirer(self.model.relations, "istio-metadata")

        self.framework.observe(self.on["istio-metadata"].relation_changed, self._on_istio_metadata_changed)
        self.framework.observe(self.on["istio-metadata"].relation_broken, self._on_istio_metadata_changed)

    def _on_istio_metadata_changed(self):
        data = istio_metadata.get_data()
        ...

Where you also add relation to your charmcraft.yaml or metadata.yaml (note that IstioMetadataRequirer is designed for relating to a single application and must be used with limit=1 as shown below):

requires:
  istio-metadata:
    limit: 1
    interface: istio_metadata
Provider

IstioMetadataProvider is a wrapper for publishing data to charms related using the istio-metadata interface. Note that IstioMetadataProvider does not manage any events, but instead provides a publish method for sending data to all related applications. Triggering publish appropriately is left to the charm author, although generally you want to do this at least during the relation_joined and leader_elected events. An example implementation is:

class FooCharm(CharmBase):
    def __init__(self, framework):
        super().__init__(framework)
        self.istio_metadata = IstioMetadataProvider(
            relation_mapping=self.model.relations,
            app=self.app,
            relation_name="istio-metadata",
        )

        self.framework.observe(self.on.leader_elected, self.do_something_to_publish)
        self.framework.observe(self._charm.on["istio-metadata"].relation_joined, self.do_something_to_publish)
        self.framework.observe(self.on.some_event_that_changes_istio_metadata, self.do_something_to_publish)

    def do_something_to_publish(self, e):
        self.istio_metadata.publish(...)

Where you also add the following to your charmcraft.yaml or metadata.yaml:

provides:
  istio-metadata:
    interface: istio_metadata

Index

class IstioMetadataAppData

Description

Data model for the istio-metadata interface. None

class IstioMetadataRequirer

Description

Endpoint wrapper for the requirer side of the istio-metadata relation. None

Methods

IstioMetadataRequirer. __init__( self , relation_mapping: RelationMapping , relation_name: str )

Initialize the IstioMetadataRequirer object.

Arguments

relation_mapping

The RelationMapping of a charm (typically self.model.relations from within a charm object).

relation_name

The name of the wrapped relation.

Description

This object is for accessing data from relations that use the istio-metadata interface. It does not autonomously handle the events associated with that relation. It is up to the charm using this object to observe those events as they see fit. Typically, that charm should observe this relation's relation-changed event.

This object is for interacting with a relation that has limit=1 set in charmcraft.yaml. In particular, the get_data method will raise if more than one related application is available.

IstioMetadataRequirer. relations( self )

Description

Return the relation instances for applications related to us on the monitored relation. None

IstioMetadataRequirer. get_data( self )

Return data for at most one related application, raising if more than one is available.

Description

Useful for charms that always expect exactly one related application. It is recommended that those charms also set limit=1 for that relation in charmcraft.yaml. Returns None if no data is available (either because no applications are related to us, or because the related application has not sent data).

class IstioMetadataProvider

Description

The provider side of the istio-metadata relation. None

Methods

IstioMetadataProvider. __init__( self , relation_mapping: RelationMapping , app: Application , relation_name: str )

Initialize the IstioMetadataProvider object.

Arguments

relation_mapping

The RelationMapping of a charm (typically self.model.relations from within a charm object).

app

This application.

relation_name

The name of the relation.

Description

This object is for serializing and sending data to a relation that uses the istio-metadata interface - it does not automatically observe any events for that relation. It is up to the charm using this to call publish when it is appropriate to do so, typically on at least the charm's leader_elected event and this relation's relation_joined event.

IstioMetadataProvider. relations( self )

Description

Return the applications related to us under the monitored relation. None

IstioMetadataProvider. publish( self , root_namespace: str )

Post istio-metadata to all related applications.

Arguments

root_namespace

The root namespace of the Istio deployment.

Description

This method writes to the relation's app data bag, and thus should never be called by a unit that is not the leader otherwise ops will raise an exception.