amaechler opened a new pull request, #20404:
URL: https://github.com/apache/druid/pull/20404
This PR adds `K8sNodeLabelDynamicConfigProvider` to
`druid-kubernetes-extensions`, registered as the `k8sNodeLabel`
`DynamicConfigProvider` subtype. It resolves configuration values from the
labels of the Kubernetes node that the Druid process runs on.
Consider this example, where we read the `topology.k8s.aws/zone-id` node
label and use it to set the `client.rack` property:
```json
"consumerProperties": {
"bootstrap.servers": "...",
"druid.dynamic.config.provider": {
"type": "k8sNodeLabel",
"labels": { "client.rack": "topology.k8s.aws/zone-id" }
}
}
```
#### Motivation
[KIP-392](https://cwiki.apache.org/confluence/display/KAFKA/KIP-392%3A+Allow+consumers+to+fetch+from+closest+replica)
lets a consumer fetch from the closest broker replica rather than the
partition leader, which for ingestion avoids paying for cross-zone traffic on
every fetch. The consumer opts in by setting `client.rack` to a value matching
the `broker.rack` of the brokers it should prefer.
Once the Kubernetes scheduler has placed a pod on a node, the rack of a task
is the zone of that node. The pod reads its own node name from `spec.nodeName`
and makes one call to the Kubernetes API server to read the node's labels.
Nothing in the provider is Kafka-specific: any property can be filled from
any node label.
#### Design
- **`labels`** maps a property to set onto the node label to read it from.
For example, with `{"client.rack": "topology.k8s.aws/zone-id"}`, a task running
on a node labelled `topology.k8s.aws/zone-id=usw2-az1` will get
`client.rack=usw2-az1`.
- **`nodeNameVariable`** is the name of the environment variable that holds
the pod's node name, since a pod does not know that on its own. It defaults to
`HOST_NODE_NAME`. If your pod template already exposes the node name under
another name, say `NODE_NAME`, set `"nodeNameVariable": "NODE_NAME"` rather
than adding a second variable.
- **Fail-open.** A key that cannot be resolved is omitted.
- **Client.** The extension's existing Kubernetes client, but its own
instance with a five-second call timeout and redirects disabled. The shared
discovery client is not reused because its read never timeout.
- **Caching.** Node labels are read once per process and cached. A failed
read is not cached, so it is retried.
#### Example
Let's say that a EKS node carries the label
`topology.k8s.aws/zone-id=usw2-az1` (the availability zone ID that MSK reports
as `broker.rack`). The pod template already exposes the node name under its own
variable name:
```yaml
env:
- name: NODE_NAME # any name works; the provider is told
which one below
valueFrom:
fieldRef:
fieldPath: spec.nodeName # the downward API fills in the node the
pod landed on
```
The supervisor spec points the provider at that variable and at the label:
```jsonc
"consumerProperties": {
"bootstrap.servers": "...",
"druid.dynamic.config.provider": {
"type": "k8sNodeLabel",
"nodeNameVariable": "NODE_NAME", // omit to use
the default, HOST_NODE_NAME
"labels": { "client.rack": "topology.k8s.aws/zone-id" } // property to
set : node label to read it from
}
}
```
The task resolves `client.rack=usw2-az1` and fetches from replicas in its
own zone. On a node without that label, `client.rack` stays unset and the
consumer fetches from the leader, as it did before.
#### Authentication and permissions
The pod authenticates to the API server with its projected service account
token. Reading a node is a cluster-scoped operation, so the service account
needs a ClusterRole granting `get` on `nodes`. The pod also needs its own node
name from the downward API, as in the example above. Both are documented on the
operations page.
#### Release note
The `druid-kubernetes-extensions` extension now provides a `k8sNodeLabel`
dynamic config provider, which resolves configuration values from the labels of
the Kubernetes node a Druid process runs on.
<hr>
##### Key changed/added classes in this PR
* `K8sNodeLabelDynamicConfigProvider`
* `NodeLabelReader`
* `ApiNodeLabelReader`
* `CachingNodeLabelReader`
* `K8sDiscoveryModule`
<hr>
This PR has:
- [x] been self-reviewed.
- [x] using the [concurrency
checklist](https://github.com/apache/druid/blob/master/dev/code-review/concurrency.md)
- [x] added documentation for new or modified features or behaviors.
- [x] a release note entry in the PR description.
- [x] added Javadocs for most classes and all non-trivial methods. Linked
related entities via Javadoc links.
- [x] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [x] added unit tests or modified existing tests to cover new code paths,
ensuring the threshold for [code
coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md)
is met.
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
