The Set Vars action is used to define or update global variables in a Traffic Policy’s runtime context. Subsequent actions or expressions can reference these variables for conditional logic through expressions or dynamic interpolation.

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Configuration Reference

This is the Traffic Policy configuration reference for this action.

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Supported Phases

on_http_request, on_http_response, on_tcp_connect

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Type

set-vars

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Configuration Fields

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vars
array of map[string]any
Required
List of maps that have a key of string and a value of any valid CEL type
Each map must be of exactly size 1, and represents one variable where the key is the name of the variable:
vars:
  - variable_a: value
  - variable_b: value

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Behavior

The set-vars action allows you to define your own global variables to be used in future actions or expressions, like this: 
on_http_request:
  - actions:
      - type: set-vars
        config:
          vars:
            - variable_a: Hello,
            - variable_b: World!
  - actions:
      - type: custom-response
        config:
          status_code: 200
          headers:
            content-type: text/plain
          body: ${vars.variable_a} ${vars.variable_b}
After being defined through the set-vars action, you can access them through CEL Interpolation or anywhere else that CEL is supported, like expressions.
You can use any valid CEL type as a variable value, including strings, booleans, doubles, null, maps, and lists.

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CEL Interpolation

Variables also support CEL interpolation (${<expression>}) in values, enabling you to create dynamic values and types: 
on_http_request:
  - actions:
      - type: set-vars
        config:
          vars:
            - message: Your IP is ${conn.client_ip}!
CEL-interpolated strings that are exactly of the form "${vars.<name>}" will resolve to the evaluated type. Strings that contain CEL-interpolated substrings within them such as sample ${conn.tls.client.pem} here will convert all CEL-interpolated substrings to strings

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Scoping

Variables you define in the set-vars action are scoped to the Traffic Policy and are not accessible outside of it. Variables defined in each of the three phases (on_http_request, on_http_response, on_tcp_connect) are scoped to that phase, and cannot be accessed in other phases.

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Referencing other variables and macros

CEL-interpolated strings may reference all other variables and macros available to traffic policies. This also includes variables previously defined in the same or previous set-vars actions. This allows for powerful dynamic behavior and customization of your Traffic Policy.

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Examples

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Basic Example

The following Traffic Policy configuration is an example configuration of the set-vars action.

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Example Traffic Policy Document

on_http_request:
  - actions:
      - type: set-vars
        config:
          vars:
            - sample_string: bar
            - sample_double: 1.5
            - sample_bool: true
            - sample_null: null
            - sample_list:
                - 1
                - 2
                - 3
            - sample_map:
                key: value
            - sample_nested_map:
                key:
                  - value1
                  - value2
  - expressions:
      - vars.sample_bool == true
    actions:
      - type: custom-response
        config:
          status_code: 200
          headers:
            content-type: text/plain
          body: ${vars.sample_string} ${vars.sample_double} ${vars.sample_list[0]} ${vars.sample_map.key} ${vars.sample_nested_map.key[1]}

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CEL Interpolation Example

The following Traffic Policy configuration is an example of using CEL-interpolation with the set-vars action.

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Example Traffic Policy Document

on_http_request:
  - actions:
      - type: set-vars
        config:
          vars:
            - sample_string: 'x-foo header: ${request.headers[''x-foo'']}'
            - sample_uint: ${uint(1.5) + 10u}
            - sample_int: ${int(50.5)}
            - sample_map:
                pem: ${conn.tls.client.pem}

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Setting Vars based on Previous Vars Example

The following Traffic Policy configuration is an example of setting vars based on previous vars with the set-vars action. Variables are determined in the order in which they are listed in the configuration list.

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Example Traffic Policy Document

on_http_request:
  - actions:
      - type: set-vars
        config:
          vars:
            - accepted_models:
                - openai/o1
                - openai/4o
                - openai/4o-mini
            - models: ${actions.ngrok.http_request.res.body}
            - models: ${vars.models.filter(model, model.id in vars.accepted_models)}
            - models: ${vars.models.filter(model, model.latency < 100)}
            - models: ${vars.models.sort(x, y, x.latency < y.latency)}