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Event Queue

Setup

Ways of Initialization

  • Run npm add @cap-js-community/event-queue in @sap/cds project
  • Initialize the event queue as CAP-Plugin or manually in your server.js

Using CDS Outbox with config.yaml

The simplest way to utilize the event-queue is by allowing it to manage the CDS outbox and outbox services via the outbox method in conjunction with the event-queue. To accomplish this, the event-queue needs to be set up as a CDS outbox. Refer to the following guides on how to configure the event-queue and how to implement a CDS service..

As cds-plugin

Extend the cds section of your package.json. Reference to the cds-plugin section in the capire documentation about the cds-plugin concept.

{
  "cds": {
    "eventQueue": {
      "configFilePath": "./srv/eventQueueConfig.yml"
    }
  }
}

in server.js

Call the initialize function in your server.js. Check here the available settings for the initialization.

eventQueue.initialize({
  configFilePath: "./srv/eventConfig.yml",
});

Initialization parameters

The table below lists the initialization parameters that can be used to configure how the event-queue operates. These parameters allow you to customize various aspects of the event processing, such as the configuration file path, event processing behavior, load balancing, and more. The table includes the parameter name, a description of its purpose, and the default value if not specified.

Name Description Default Can be changed at runtime
configFilePath Path to the configuration file. null no
registerAsEventProcessor Whether or not to register as an event processor. If false, the app can publish events but doesn’t process events. true no
processEventsAfterPublish Whether or not to process events immediately after publish. Events are distributed via Redis to all available app instances. true no
isEventQueueActive Determines if the event queue is active. This property controls whether events are automatically processed. It can be modified in real-time to temporarily disable periodic runs. true yes
runInterval [ms] The interval in milliseconds at which the runner runs. 25 _ 60 _ 1000 yes
disableRedis Whether or not to disable Redis. false no
updatePeriodicEvents Whether or not to update periodic events. true no
thresholdLoggingEventProcessing [ms] Threshold after how many milliseconds the processing of a event or periodic event is logged for observability. 50 yes
useAsCAPOutbox Uses the event-queue as the outbox of CAP. Outbox called are stored and processed in the event-queue instead of the outbox of CAP. false no
userId User id for all created cds contexts. This influences the value for updated managed database fields like createdBy and modifiedBy. false yes
cleanupLocksAndEventsForDev Deletes all semantic locks and sets all events that are in progress to error during server start. This is used to clean up leftovers from server crashes or restarts during processing. false no
redisOptions The option is provided to customize settings when creating Redis clients. The object is spread at the root level for creating a client and within the default options for cluster clients. {} no
insertEventsBeforeCommit If enabled, this feature allows events (including those for outboxed services) to be inserted in bulk using the before commit handler. This is performed to improve performance by mass inserting events instead of single insert operations. false no

Configure Redis

To take advantage of the event-queue capabilities that come with Redis, you simply need to bind a Redis instance to the app where the event-queue will be used. No additional steps are required. Please note that the event-queue supports both single and cluster Redis instances.