The Eventide component runner just got a nice little update for both developers and operators of Eventide services: A service now outputs a comprehensive description of a service’s contents and the environment.

Example

Here’s an example from Eventide’s account example component:

ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-darwin19]

Environment Variables:
  ENTITY_CACHE_SCOPE: exclusive
  MESSAGE_STORE_SETTINGS_PATH: (not set)
  HANDLE_STRICT: (not set)
  LOG_LEVEL: (not set)
  LOG_TAGS: (not set)
  STARTUP_INFO: (not set)
  ENV_VAR_INFO: (not set)

Host: account-component

  Component: AccountComponent::Start (Name: (none))

    Consumer: AccountComponent::Consumers::Commands
      Category: account:command
      Position: 5
      Identifier: (none)
      Correlation: (none)
      Position Stream: account:command+position

      Handlers:
        Handler: AccountComponent::Handlers::Commands
          Messages: Open, Close, Deposit, Withdraw

    Consumer: AccountComponent::Consumers::Commands::Transactions
      Category: accountTransaction
      Position: 0
      Identifier: (none)
      Correlation: (none)
      Position Stream: accountTransaction:position

      Handlers:
        Handler: AccountComponent::Handlers::Commands::Transactions
          Messages: Deposit, Withdraw

Host running: account-component
Process ID: 41880

New Gems

The new startup input is included as of the evt-component_host v2.0.0.5 gem, the evt-consumer v2.2.0.1 gem, and the evt-consumer-postgres v2.3.0.1 gem, and also depends on updates to the evt-messaging v2.5.1.0 gem.

Refreshing a component’s gems will apply all of these changes implicitly.

The Included Startup Info

The startup info includes details about components, consumers, streams, handlers, and messages, as well as environment variables used to override Eventide’s runtime options, and the Ruby runtime.

Component Information

The component information includes:

• Component host name
• Components run by the host
• Consumers within the component
• The category stream processed by a consumer
• Handlers within a consumer that receives messages dispatched from the consumer dispatches
• Messages that a handler receives from the consumer

The consumer’s info also includes:

• The global position of the message that the consumer is starting from
• The consumer’s identifier
• The consumer’s Pub/Sub correlation
• The consumer’s position stream

The consumer’s info also may optionally include:

• Consumer optional group member and consumer group size
• Consumer’s optional SQL query condition for filtering consumed messages.

Environment Variable Information

The information printed when a service is starting also includes the environment variables that override some of Eventide’s default behaviors.

The environment variable information includes:

• ENTITY_CACHE_SCOPE
• MESSAGE_STORE_SETTINGS_PATH
• HANDLE_STRICT
• LOG_LEVEL
• LOG_TAGS
• STARTUP_INFO
• ENV_VAR_INFO

Controlling the Component Startup Information Output

The component startup information output is controlled by the STARTUP_INFO environment variable.

The variable’s default value is “on”.

To deactivate the printing of the component startup information, set the STARTUP_INFO to “off”.

STARTUP_INFO=off start_service.rb

Controlling the Environment Variable Information Output

The environment variable information output is controlled by the ENV_VAR_INFO environment variable.

The variable’s default value is “on”.

To deactivate the printing of the environment variables list, set the ENV_VAR_INFO to “off”.

ENV_VAR_INFO=off start_service.rb

Log Output

All of the startup info is also output by the logger at the info level.

To output the startup info to the logger, set the LOG_TAGS environment variable to start.

LOG_TAGS=start start_service.sh

The logger outputs all of the regular startup info detailed above, as well as:

• The consumer’s message reader’s retrieval batch size
• The consumer’s position update interval
• The consumer’s poll interval in milliseconds

Conclusion

This small change to the Eventide stack puts essential feedback about the makeup of a service’s components directly into the hands of developers and operators at startup without any extra effort, and without having to inspect logs.

This feature is one of a handful of affordances to be released in the coming months that will make your experience of the award-winning Eventide stack even more polished and enjoyable.

Look for more usability improvements to critical areas of the Eventide stack like testing, integration with Rails, and monitoring.

In the mean time, sign up for the Eventide Slack and join the conversation!