How to output a message after all the input messages were processed

[mihaitodor]

You can use the sequence input to have a generate input fire off a message for the last event. In the example below, the first generate input is just a placeholder for a finite input. If your input is already generate, you might be tempted to increment count by one to get an extra message so you don't need the sequence input, but that's unreliable because the generate input can emit multiple messages in parallel, so your final message could land in the output before all the others have been written.

input:
  sequence:
    inputs:
      - generate:
          count: 2
          mapping: root = "foo"
      - generate:
           count: 1
           mapping: root = "end"
  processors:
    - switch:
        - check: content() == "foo"
          processors:
            - sleep:
                duration: 1s

output:
  switch:
    cases:
      - check: content() == "foo"
        output:
          stdout: {}
        processors:
          - log:
              message: "First output"
      - output:
          stdout: {}
        processors:
          - log:
              message: "Second output"