Chris Egerton created KAFKA-9560:
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Summary: Connector::validate is utilized concurrently by the
framework, but not documented as thread-safe
Key: KAFKA-9560
URL: https://issues.apache.org/jira/browse/KAFKA-9560
Project: Kafka
Issue Type: Bug
Components: KafkaConnect
Reporter: Chris Egerton
Requests to the {{PUT /connector-plugins/\{connectorType}/config/validate}}
endpoint are [delegated to the
herder|https://github.com/apache/kafka/blob/16ee326755e3f13914a0ed446c34c84e65fc0bc4/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/rest/resources/ConnectorPluginsResource.java#L81],
which [caches connector
instances|https://github.com/apache/kafka/blob/16ee326755e3f13914a0ed446c34c84e65fc0bc4/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/AbstractHerder.java#L536-L544]
that are used [during config
validation|https://github.com/apache/kafka/blob/16ee326755e3f13914a0ed446c34c84e65fc0bc4/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/AbstractHerder.java#L310].
This has the effect that, should concurrent requests to that endpoint occur
for the same connector type, the same connector instance may be responsible for
[validating those
configurations|https://github.com/apache/kafka/blob/16ee326755e3f13914a0ed446c34c84e65fc0bc4/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/AbstractHerder.java#L334]
concurrently _(may_ instead of _will_ because there is also a race condition
in the {{AbstractHerder::getConnector}} method that potentially fails to detect
that an instance of the connector has already been created and, as a result,
creates a second instance).
This is slightly problematic because the
[Connector::validate|https://github.com/apache/kafka/blob/16ee326755e3f13914a0ed446c34c84e65fc0bc4/connect/api/src/main/java/org/apache/kafka/connect/connector/Connector.java#L122-L127]
method is not marked as thread-safe. However, because a lot of connectors out
there tend to use the default implementation for that method, it's probably not
super urgent that we patch this immediately.
A couple of options are:
# Update the docs for that method to specify that it must be thread-safe
# Rewrite the connector validation logic in the framework to avoid
concurrently invoking {{Connector::validate}} on the same instance.
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