Use variables in Workflow Links

When you create Workflow Links, you use variables in the Name and URL so that span-specific content displays. Variables use the Mustache syntax.

For example, in this link definition:

{
  "$service": null,
  "$hasError": [true],
  "MY_ERROR_TYPE_ATTRIBUTE": null
}
      

Both {{$service}} and {{MY_ERROR_TYPE_ATTRIBUTE}} are variables. The {{$service}} variable resolves to the span’s service and is a Cloud Observability variable (denoted by the $). The {{MY_ERROR_TYPE_ATTRIBUTE}} represents a user-defined variable. User-defined variables don’t use the $. Here, it represents an attribute on a span. Any attribute you have on your spans can be used as a variable.

User-defined variables

The attributes that you create in your tracing code can be used as variables in Workflow Links. For example, if you’ve created the error_type attribute in your code like this:

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Span span = tracer.spanBuilder("/project/:project-id/list") // operation named after the route
                 .setSpanKind(Span.Kind.CLIENT) // tag the span as a service boundary
                 .startSpan();

  span.setAttribute("error_type_", "world");
  span.end()

Then you can use the {{error_type}} variable in your links. However, you need to be sure that the attribute exists for the span. The easiest way to do this is to view the sidebar on the Trace View page. Attributes are listed for the span there.

Cloud Observability variables

The following are the Cloud Observability-specific variables that you can use in your Workflow Link names, URLs, and rules. Many of these also appear in the sidebar of the Trace View page.

Be sure to use a $ in front of all Cloud Observability variables.

Span variables

These variables provide information about a span.

Time-based variables

These variables provide time information about the span.

Miscellaneous variables

See also

Create and manage Workflow Links

Workflow Links cookbook

Updated Dec 1, 2019