Status

Current state: [ UNDER DISCUSSION | ACCEPTED | REJECTED ]

Discussion thread: <link to mailing list DISCUSS thread>

JIRA: SAMZA-TBD

Released: 

Problem

Samza Yarn follows a multi-stage deployment model, where Job Runner, which runs on the submission host, reads configuration, performs planning and persist config in the coordinator stream before submitting the job to Yarn cluster. In Yarn, Application Master (AM) reads config from coordinator stream before spinning up containers to execute. Split of responsibility between job runner and AM is operationally confusing, and makes debugging the pipeline difficult with multiple points of failure. In addition, since planning invokes user code, it usually requires isolation on the runner from security perspective to guard the framework from malicious user code, or a malicious user can gain access to other user jobs running on the same runner. 

Proposed Changes

We will provide a plugable config retrieval interface on AM, when used, will simplify the job submission to Yarn, without involving any complex logic. AM on the other hand, will read job config using the provided config loader, performs planning, generate DAG and persist the final config back to coordinator stream.

Public Interfaces

We will introduce two job configs to configure the job to use the alternative workflow:

• job.config.loader.class
• job.config.loader.properties

The changes are fully backward compatible. For people who are interested in using the new workflow, simplify supply "job.config.loader.class" and "job.config.loader.properties". For example, in Hello Samza example, application will be invoked by

deploy/samza/bin/run-app.sh \
  --config-factory=org.apache.samza.config.factories.PropertiesConfigFactory \
  --config-path=file://$PWD/deploy/samza/config/wikipedia-feed.properties \
  --config job.config.loader.class=org.apache.samza.config.loader.PropertiesConfigLoader \
  --config job.config.loader.properties.path=./__package/config/wikipedia-feed.properties

Implementation and Test Plan

JobConfig

We will add two new configs in JobConfig to control whether to read AM from ConfigLoader instead of coordinator stream.

// Configuration to a fully qualified class name to load config from.
public static final String CONFIG_LOADER_CLASS = "job.config.loader.class";
// Properties needed for the config loader to load config.
public static final String CONFIG_LOADER_PROPERTIES_PREFIX = "job.config.loader.properties.";

ConfigLoader

Interface which AM relies on to read configuration from. It takes in a properties map, which defines the variables it needed in order to get the proper config.

public interface ConfigLoader {
  /**
   * Build a specific Config.
   * @param properties Resource containing information necessary for this Config.
   * @return Newly constructed Config.
   */
  Config getConfig(Config properties);
}

PropertiesConfigLoader

Default implementation of ConfigLoader, which reads "path" from the input properties, which leads to a property file.

public class PropertiesConfigLoader extends ConfigLoader {
  /**
   * Build a specific Config.
   * @param properties Resource containing information necessary for this Config.
   * @return Newly constructed Config.
   */
  override def getConfig(config: MapConfig): Config = {
    val path = config.get(JobConfig.CONFIG_LOADER_PROPERTIES_PREFIX + "path")

    val props = new Properties()
    val in = new FileInputStream(path)

    props.load(in)
    in.close()

    debug("got config %s from config %s" format (props, path))

    new MapConfig(props.asScala.asJava)
  }
}

RemoteApplicationRunner

Depending on the existence of "job.config.loader.class" and "job.config.loader.properties", RemoteApplicationRunner#run will keep its current behavior or simplify submit the job to Yarn.

@Override
  public void run(ExternalContext externalContext) {
    if (new JobConfig(config).getConfigLoaderClass() != null) {
      JobRunner runner = new JobRunner(config);
      runner.getJobFactory().getJob(config).submit();
    } else {
      // Keep existing behavior
    }

YarnJob

YarnJob#buildEnvironment will build coordinator stream env variable or config loader env variable based on the existence of "job.config.loader.class" and "job.config.loader.properties".

private[yarn] def buildEnvironment(config: Config, yarnConfig: YarnConfig,
    jobConfig: JobConfig): Map[String, String] = {
    val envMapBuilder = Map.newBuilder[String, String]

    if (jobConfig.getConfigLoaderClass != null) {
      envMapBuilder += ShellCommandConfig.ENV_REMOTE_CONFIG_FACTORY ->
        Util.envVarEscape(SamzaObjectMapper.getObjectMapper.writeValueAsString(jobConfig.getRemoteConfigFactoryClassName))
      envMapBuilder += ShellCommandConfig.ENV_REMOTE_CONFIG_PROPERTIES ->
        Util.envVarEscape(SamzaObjectMapper.getObjectMapper.writeValueAsString(jobConfig.getRemoteConfigProperties))
    } else {
      val coordinatorSystemConfig = CoordinatorStreamUtil.buildCoordinatorStreamConfig(config)
      envMapBuilder += ShellCommandConfig.ENV_COORDINATOR_SYSTEM_CONFIG ->
        Util.envVarEscape(SamzaObjectMapper.getObjectMapper.writeValueAsString(coordinatorSystemConfig))
    }

ClusterBasedJobCoordinator

ClusterBasedJobCoordinator#main will construct the application config through coordinator stream or config loader, depending on the env variables it get.

Compatibility, Deprecation, and Migration Plan

Fully backward compatible, jobs can still follow the existing workflow. We will gradually deprecate the current flow and make the two new configs required.