[AdminApi] Dynamically Changing Cluster-Wide Configs does not work

[twiechert]

Description

Analyzing the bundled kafka client tools, the admin protocol expects resource name set to <default> when dynamically changing cluster-wide properties. However, trying to change a cluster property such as background.threads referring to ConnfigResource.name == <default>yields the following error generated in librdkafka.

error: Expected an int32 broker_id for ConfigResource(type=BROKER, name=<default>)

I am not sure if this is a limitation of the librdkafka implementation in general or the way the go client interacts with the librdkafka api.

How to reproduce

    var cfgEntry = kafka.ConfigEntry{Name: "background.threads", Value: "11", Operation: kafka.AlterOperationSet}

        var resourceType, _ = kafka.ResourceTypeFromString("BROKER")
        cfg[0] = cfgEntry
        configResource := kafka.ConfigResource{Type: resourceType, Name: "<default>", Config: cfg}
        configResources[0] = configResource
        if result, e := c.AlterConfigs(ctx, configResources); e == nil {
            log.Info(fmt.Sprintf("Successfully applied %v changes.", len(result)))
        } 

Checklist

Please provide the following information:

• [x] confluent-kafka-go and librdkafka version (LibraryVersion()): gopkg.in/confluentinc/confluent-kafka-go.v1 v1.1.0

• [x] Apache Kafka broker version: 2.1.1

• [x] Client configuration: ConfigMap{...} through SASL, but generally no connection issue

• [ x] Operating system: client osx, kafka on docker

• [ x] Provide client logs (with "debug": ".." as necessary)

  %7|1573577490.061|ADMINFAIL|rdkafka#producer-1| [thrd:app]: Admin ALTERCONFIGS result error: Expected an int32 broker_id for ConfigResource(type=BROKER, name=<default>)

• [x] Provide broker log excerpts not reaching the broker

• [ ] Critical issue

[edenhill]

Good find, seems like we need to add support for default entity names. In the case of BROKER the default name is empty, which I believe the librdkafka API disallows at this point.