In addition to out-of-the-box schedulers for Aurora, Heron can also be deployed in a local environment, which stands up a mock Heron cluster on a single machine. This can be useful for experimenting with Heron’s features, testing a wide variety of possible cluster events, and so on.

One of two state managers can be used for coordination when deploying locally:

Note: Deploying a Heron cluster locally is not to be confused with Heron’s simulator mode. Simulator mode enables you to run topologies in a cluster-agnostic JVM process for the purpose of development and debugging, while the local scheduler stands up a Heron cluster on a single machine.

How Local Deployment Works

Using the local scheduler is similar to deploying Heron on other schedulers. The Heron cli is used to deploy and manage topologies as would be done using a distributed scheduler. The main difference is in the configuration.

Local Scheduler Configuration

To configure Heron to use local scheduler, specify the following in scheduler.yaml config file.

  • heron.class.scheduler — Indicates the class to be loaded for local scheduler. Set this to com.twitter.heron.scheduler.local.LocalScheduler

  • heron.class.launcher — Specifies the class to be loaded for launching topologies. Set this to com.twitter.heron.scheduler.local.LocalLauncher

  • — Provides the working directory for topology. The working directory is essentially a scratch pad where topology jars, heron core release binaries, topology logs, etc are generated and kept.

  • heron.package.core.uri — Indicates the location of the heron core binary package. The local scheduler uses this URI to download the core package to the working directory.

  • — Specifies the java home to be used when running topologies in the containers. Set to ${JAVA_HOME} to use the value set in the bash environment variable $JAVA_HOME.

Example Local Scheduler Configuration

# scheduler class for distributing the topology for execution
heron.class.scheduler: com.twitter.heron.scheduler.local.LocalScheduler

# launcher class for submitting and launching the topology
heron.class.launcher: com.twitter.heron.scheduler.local.LocalLauncher

# working directory for the topologies ${HOME}/.herondata/topologies/${CLUSTER}/${TOPOLOGY}

# location of the core package
heron.package.core.uri: file://${HERON_DIST}/heron-core.tar.gz

# location of java - pick it up from shell environment ${JAVA_HOME}