fix(dataflow): make each replica use unique subscription names

Following #6020, it was no longer possible to have multiple replicas of
dataflow-engine subscribing simultaneously to the scheduler, because
all were connecting with the same subscriber name, and a lock was added
per name, first waiting the disconnection of the old subscriber before
allowing a new one to progress.

We update the dataflow-engine code so that each replica connects with
its own hostname as the subscriber name. If the hostname can not
be determined, we subscribe with the name `seldon-dataflow-engine-` followed
by a hex string of 50 random characters.

The subscriber name can also be explicitly controlled by passing the
`--dataflow-replica-id` argument or the `DATAFLOW_REPLICA_ID` environment
variable, wich will take precedence, in that order, to setting the value
as the hostname.

scheduler/data-flow/src/main/kotlin/io/seldon/dataflow/Cli.kt

@@ -11,6 +11,7 @@ package io.seldon.dataflow
 
 import com.natpryce.konfig.CommandLineOption
 import com.natpryce.konfig.Configuration
+import com.natpryce.konfig.ConfigurationMap
 import com.natpryce.konfig.ConfigurationProperties
 import com.natpryce.konfig.EnvironmentVariables
 import com.natpryce.konfig.Key
@@ -25,6 +26,7 @@ import io.klogging.Level
 import io.klogging.noCoLogger
 import io.seldon.dataflow.kafka.security.KafkaSaslMechanisms
 import io.seldon.dataflow.kafka.security.KafkaSecurityProtocols
+import java.net.InetAddress
 
 object Cli {
     private const val ENV_VAR_PREFIX = "SELDON_"
@@ -34,6 +36,7 @@ object Cli {
     val logLevelApplication = Key("log.level.app", enumType(*Level.values()))
     val logLevelKafka = Key("log.level.kafka", enumType(*Level.values()))
     val namespace = Key("pod.namespace", stringType)
+    val dataflowReplicaId = Key("dataflow.replica.id", stringType)
 
     // Seldon components
     val upstreamHost = Key("upstream.host", stringType)
@@ -75,6 +78,7 @@ object Cli {
             logLevelApplication,
             logLevelKafka,
             namespace,
+            dataflowReplicaId,
             upstreamHost,
             upstreamPort,
             kafkaBootstrapServers,
@@ -105,10 +109,26 @@ object Cli {
 
     fun configWith(rawArgs: Array<String>): Configuration {
         val fromProperties = ConfigurationProperties.fromResource("local.properties")
+        val fromSystem = getSystemConfig()
         val fromEnv = EnvironmentVariables(prefix = ENV_VAR_PREFIX)
         val fromArgs = parseArguments(rawArgs)
 
-        return fromArgs overriding fromEnv overriding fromProperties
+        return fromArgs overriding fromEnv overriding fromSystem overriding fromProperties
+    }
+
+    private fun getSystemConfig(): Configuration {
+        val dataflowIdPair = this.dataflowReplicaId to getDataflowId()
+        return ConfigurationMap(dataflowIdPair)
+    }
+
+    private fun getDataflowId(): String {
+        return try {
+            InetAddress.getLocalHost().hostName
+        } catch (e: Exception) {
+            val hexCharPool: List<Char> = ('a'..'f') + ('0'..'9')
+            val randomIdLength = 50
+            return "seldon-dataflow-engine-" + List(randomIdLength) { hexCharPool.random() }.joinToString("")
+        }
     }
 
     private fun parseArguments(rawArgs: Array<String>): Configuration {

scheduler/data-flow/src/main/kotlin/io/seldon/dataflow/Main.kt

@@ -102,9 +102,11 @@ object Main {
                 describeRetries = config[Cli.topicDescribeRetries],
                 describeRetryDelayMillis = config[Cli.topicDescribeRetryDelayMillis],
             )
+        val subscriberId = config[Cli.dataflowReplicaId]
+
         val subscriber =
             PipelineSubscriber(
-                "seldon-dataflow-engine",
+                subscriberId,
                 kafkaProperties,
                 kafkaAdminProperties,
                 kafkaStreamsParams,

scheduler/data-flow/src/main/resources/local.properties

@@ -1,5 +1,6 @@
 log.level.app=INFO
 log.level.kafka=WARN
+dataflow.replica.id=seldon-dataflow-engine
 kafka.bootstrap.servers=localhost:9092
 kafka.consumer.prefix=
 kafka.security.protocol=PLAINTEXT

scheduler/data-flow/src/test/kotlin/io/seldon/dataflow/CliTest.kt

@@ -16,9 +16,12 @@ import org.junit.jupiter.params.provider.Arguments
 import org.junit.jupiter.params.provider.Arguments.arguments
 import org.junit.jupiter.params.provider.MethodSource
 import strikt.api.expectCatching
+import strikt.api.expectThat
 import strikt.assertions.isEqualTo
+import strikt.assertions.isNotEqualTo
 import strikt.assertions.isSuccess
 import java.util.stream.Stream
+import kotlin.test.Test
 
 internal class CliTest {
     @DisplayName("Passing auth mechanism via cli argument")
@@ -36,6 +39,20 @@ internal class CliTest {
             .isEqualTo(expectedMechanism)
     }
 
+    @Test
+    fun `should handle dataflow replica id`() {
+        val cliDefault = Cli.configWith(arrayOf<String>())
+        val testReplicaId = "dataflow-id-1"
+        val cli = Cli.configWith(arrayOf("--dataflow-replica-id", testReplicaId))
+
+        expectThat(cliDefault[Cli.dataflowReplicaId]) {
+            isNotEqualTo("seldon-dataflow-engine")
+        }
+        expectThat(cli[Cli.dataflowReplicaId]) {
+            isEqualTo(testReplicaId)
+        }
+    }
+
     companion object {
         @JvmStatic
         private fun saslMechanisms(): Stream<Arguments> {