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connectivity_issues.md

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Network connectivity issues between Spark components

Network connectivity issues between Spark components can lead to a variety of warnings / errors:

  • SparkContext <-> Spark Standalone Master:

    If the SparkContext cannot connect to a Spark standalone master, then the driver may display errors like

    ERROR AppClient$ClientActor: All masters are unresponsive! Giving up.
ERROR SparkDeploySchedulerBackend: Spark cluster looks dead, giving up.
ERROR TaskSchedulerImpl: Exiting due to error from cluster scheduler: Spark cluster looks down

    If the driver is able to connect to the master but the master is unable to communicate back to the driver, then the Master's logs may record multiple attempts to connect even though the driver will report that it could not connect:

    INFO Master: Registering app SparkPi
INFO Master: Registered app SparkPi with ID app-XXX-0000
INFO: Master: Removing app app-app-XXX-0000
[...]
INFO Master: Registering app SparkPi
INFO Master: Registered app SparkPi with ID app-YYY-0000
INFO: Master: Removing app app-YYY-0000
[...]

    In this case, the master reports that it has successfully registered an application, but if the acknowledgment of this registration fails to be received by the driver, then the driver will automatically make several attempts to re-connect before eventually giving up and failing. As a result, the master web UI may report multiple failed applications even though only a single SparkContext was created.

Recomendations

If you are experiencing any of the errors described above:

  • Check that the workers and drivers are configured to connect to the Spark master on the exact address listed in the Spark master web UI / logs.
  • Set SPARK_LOCAL_IP to a cluster-addressable hostname for the driver, master, and worker processes.

Configurations that determine hostname/port binding:

This section describes configurations that determine which network interfaces and ports Spark components will bind to.

In each section, the configurations are listed in decreasing order of precedence, with the final entry being the default configuration if none of the previous configurations were supplied.

SparkContext actor system:

Hostname:

  • The spark.driver.host configuration property.
  • If the SPARK_LOCAL_IP environment variable is set to a hostname, then this hostname will be used. If SPARK_LOCAL_IP is set to an IP address, it will be resolved to a hostname.
  • The IP address of the interface returned from Java's InetAddress.getLocalHost method.

Port:

  • The spark.driver.port configuration property.
  • An ephemeral port chosen by the OS.

Spark Standalone Master / Worker actor systems:

Hostname:

  • The --host, or -h options (or the deprecated --ip or -i options) when launching the Master or Worker process.
  • The SPARK_MASTER_HOST environment variable (only applies to Master).
  • If the SPARK_LOCAL_IP environment variable is set to a hostname, then this hostname will be used. If SPARK_LOCAL_IP is set to an IP address, it will be resolved to a hostname.
  • The IP address of the interface returned from Java's InetAddress.getLocalHost method.

Port:

  • The --port, or -p options when launching the Master or Worker process.
  • The SPARK_MASTER_PORT or SPARK_WORKER_PORT environment variables (only apply to Master and Worker, respectively).
  • An ephemeral port chosen by the OS.