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title: Intro to Heron Configuration

Heron can be configured at two levels:

1. The system level --- System-level configurations apply to the whole Heron cluster rather than to any specific topology.
2. The topology level --- Topology configurations apply only to a specific topology and can be modified at any stage of the topology's lifecycle.

All system-level configs and topology-level defaults are declared in a YAML config file in heron/config/heron_internals.yaml in the Heron codebase. You can leave that file as is when compiling Heron or modify the values to suit your use case.

The System Level

There are a small handful of system-level configs for Heron. These are detailed in System-level Configuration.

The Topology Level

There is a wide variety of topology-level configurations that you can establish as defaults in your Heron cluster. These configurations tend to apply to specific components in a topology and are detailed in the docs below:

• Heron Instance
• Heron Metrics Manager
• Heron Topology Master
• Heron Stream Manager

Overriding Topology-level Defaults

The parameters set in heron/config/heron_internals.yaml are defaults that will be automatically applied to all topologies in your cluster. You can override these values on a per-topology basis using scheduler overrides. These overrides are the second argument in all topology management commands and have the following syntax:

param1:value1 param2:value2 param3:value3 ...

Here's an example:

$ heron-cli submit "topology.debug:false heron.local.working.directory:/path/to/dir" \
    /path/to/topology/my-topology.jar \
    biz.acme.topologies.MyTopology \
    my-topology

More on Heron's CLI tool can be found in Managing Heron Topologies.