The cb Connector

info

This connector is not intended for production use, but for testing the Tremor runtime itself. To enable it pass --debug-connectors to tremor.

The cb connector is for testing circuit breaker internals.

The connector expects a circuit breaker event for each event propagated and then, the latest after a configurable timeout has been exceeded, it halts or exits the tremor process and reports on the validation result via stdout.

Most of the time it is used to test the behaviour of the whole runtime when it comes to the circuit breaker and guaranteed delivery (ack/fail) mechanisms. To that end use the connector as source and sink of events by connecting your tremor pipeline application with the in and out port of this connector. It can also be used to test the behaviour of connectors acting as event sinks, checking if they handle all events correctly, in this case connect the in port of the connector to test against to the out port of the cb connector via a pipeline of your choice.

Ports

• in: This Connector is expecting events that trigger certain Circuit Breaker and/or Event acknowledge/fail behaviour. See Expected Input Data.
• out: When configured with paths this connector will emit events on the out port.

Configuration

Config Option	Description	Possible Values	Required / Optional	Default Value
paths	A list of paths to files to load data from. Each file will be split into lines and each line will form one event. Only required for the source part.	array of strings	Only required for the source part.
timeout	Timeout in nanoseconds to wait for circuit breaker messages after all events from the paths files have been sent. After this timeout is expired the Tremor process will be stopped.	positive integer	optional	10_000_000_000 (10 seconds)
expect_batched	When set to true changes verifcation mode for testing applications involving batching. That means only not all events are required to be acknowledged, only all batches.	boolean	optional	false

Example

cb_example.troy

define flow cb_example
flow
  use tremor::pipelines;
  use std::time::nanos;

  define connector my_cb from cb
  with
    codec = "json",     # Events are line delimited JSON
    config = {
      "paths": ["in.json"], # Files from which to replay events
      "timeout": nanos::from_seconds(1)
    }
  end;
  create connector my_cb;

  create pipeline passthrough from pipelines::passthrough;

  # connect both the `out` and the `in` port of the connector 
  # via a simple passthrough pipeline.
  # (The ports can also be omitted for brevity)
  connect /connector/my_cb/out to /pipeline/passthrough/in;
  connect /pipeline/passthrough/out to /connector/my_cb/in;
end;

deploy flow cb_example;

Expected Data Format

This connector expects events that can trigger certain Circuit Breaker and Event acknowledgement behaviour via its in port.

The event can contain the cb specific payload in either the event metadata or the event payload.

The expected is a JSON document with a string or array beneath the key "cb".

The "cb" values can be one of the following (or multiple):

Value	Description
ack	Send a runtime-internal message upstream in order to acknowledge the event.
fail	Send a runtime-internal message upstream in order to fail the event.
close / trigger	Close or trigger the circuit breaker, so that all upstream connectors stop sending events until it is opened again.
open / restore	Open or restore the circuit breaker, so that all upstream connectors start sending events again.

info

Only 1 value of the pairs ack - fail and open / restore and close / trigger will be considered.

Examples

{ "cb": "ack" }    // this will acknowledge the event
{ "cb": "open" }   // this will open the circuit breaker
{ "cb": ["fail", "trigger"] } // this will fail the event and close the circuit breaker

Example usage

Name	Description
Validate dead ends are dropped	All required circuit breaker events are received and processed correctly
Validate pipeline to pipeline	All required circuit breaker events are received and processed correctly
Validate auto-acknowledged sinks	All required circuit breaker events are received and processed correctly