Field Dynamic Variable

In many scenarios, we need to dynamically obtain a field in the event. For example:

• The topic in the kafka sink, or the index in the elasticsearch sink, is dynamically generated according to the value of a field in the event. We can use ${a.b} to get value.
• In transformer interceptor, operate a field: copy(a.b, a.c).

Take the following event is an example:

{
    "fields": {
        "svc": "test",
    }
}

The kafka sink topic is configured as log-${fields.svc}, and finally generated as log-test.

Caution

You can generally use . to denote nested fields. However, if the field itself contains ., it needs to be [] enclosed to avoid mistaking it for a nested field. For example:

{
    "fields": {
        "a.b": "demo",
    }
}

Use ${fields.[a.b]} to represent a.b.