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Configuration loading chain

Zoe has a complex and powerful configuration override chain that makes it highly configurable.

Zoe configuration properties are considered in the following order (in a decreasing order of priority):

  1. ZOE_CONFIG_OVERRIDE_{env} environment variable.
  2. ZOE_CONFIG_OVERRIDE environment variable.
  3. ~/.zoe/config/{env}.yml or .json file
  4. ~/.zoe/config/common.yml or .json file

The 2 first environment variables must contain the configuration (or a subset) in json format.

The final zoe configuration will be the result of merging all the above configuration values in the increasing level priority.

The special common.yml configuration file is supposed to contain configuration values that are common to all the environments. Registered expressions or secrets providers are a good use case.

Environment variables substitutions

It is possible to use environment variables inside the zoe yaml or json configuration files and zoe will automatically substitute those variables at runtime from the environment.

The following example shows the use of an environment variable inside a yaml configuraiton file:

clusters:

  my-cluster:
    props:

      bootstrap.servers: ${BOOTSTRAP_SERVER}
      key.deserializer: org.apache.kafka.common.serialization.StringDeserializer
      value.deserializer: io.confluent.kafka.serializers.KafkaAvroDeserializer
    registry: ${SCHEMA_REGISTRY:-localhost:8081}

runners:
    default: local

With the above configuration, zoe replaces the ${BOOTSTRAP_SERVER} and ${SCHEMA_REGISTRY} expressions with the value of the environment variables BOOTSTRAP_SERVER and SCHEMA_REGISTRY respectively. If the SCHEMA_REGISTRY is not found, the specified default value is used (localhost:8081 in this case). If no default value is specified and no environment variable with the corresponding name exists, the expression is simply not replaced.

The following command should make the previous statement clearer:

BOOTSTRAP_SERVER=localhost:9092 zoe -o table config clusters list

┌────────────┬────────────────┬────────────────┬────────┬────────┐
│ cluster    │ brokers        │ registry       │ topics │ groups │
├────────────┼────────────────┼────────────────┼────────┼────────┤
│ my-cluster │ localhost:9092 │ localhost:8081 │        │        │
└────────────┴────────────────┴────────────────┴────────┴────────┘