Preprocessor Rule Conditions

You can configure Tanzu Observability by Wavefront with proxy preprocessor rules that apply only when multiple conditions are met or when certain conditions are met and other conditions are not met.

Conditional Preprocessor Rule Example

For example, you might want to block list spans only if it

• has span tags that match both "span.kind"="server" and ("http.status_code"="302" or "http.status_code"="404")
• and has no span tags that match debug=true

You can use the if parameter to fine-tune when a rule applies. Here are the rules for the example above.

• Proxy 9 and Later
• Earlier Proxy Versions

## drop spans that match the following:
## "span.kind"="server" and ("http.status_code"="302" or "http.status_code"="404")
'2878':
    - rule: test-block-list
      action: spanBlock
      if: >
        {{http.status_code}} in ("302", "404") and {{span.kind}} = "server"
        and not {{debug}} = "true"
    

  ## drop spans that match the following:
  ## "span.kind"="server" and ("http.status_code"="302" or "http.status_code"="404")
  '2878':
    - rule: test-block-list
      action: spanBlock
      if:
        all:
          - equals:
              scope: http.status_code
              value: ["302, 404"]
          - equals:
              scope: span.kind
              value: "server"
          - none:
            - equals:
                scope: debug
                value: "true"

          

The if parameter is always followed by just one operator, one of the following:

• Comparison operators with scope and value for each.
• Logical operators followed by comparison operators with scope and value for each.

Comparison Operators

With each comparison operator you specify the scope and the value.

Example

## Block list spans that have a tag "http.status_code"="302" or "http.status_code"="404"
'2878':
  - rule: test-spanblock-list
    action: spanBlock
    if:
      equals:
        scope: http.status_code
        value: ["302, 404"]

Scope

The scope is one of the following:

The value can be a string or a list of string values.

Definition

Comparison operators work exactly the way they do in Java.

Logical Operators

Logical operators support nesting in any proxy preprocessor rule. The logical operator always requires comparison operators with a scope and a value, as shown in the following example of nested operators.

In the example below, the rule applies only if at least one of the specified conditions are met:

• The sourceName has the value prod and a metricName has the value mymetric..
• The metricName starts with the string mymetric.prod.
• The env point tag is equal to prod

## Example showing nested predicates: The below rule allows all "prod" metrics.
'2878':
  - rule: test-allow-list
    action: allow
    if:
      any:
        - all:
          - contains:
              scope: sourceName
              value: "prod"
          - startsWith:
              scope: metricName
              value: "mymetric.prod"
          - equals:
              scope: env
              value: "prod"

Here are examples for each logical operator: