Send message to Pub/Sub topic

  • Article

Availability

Important

This feature is available in the Premium and Developer tiers of API Management.

The publish-to-dapr policy instructs API Management gateway to send a message to a Dapr Publish/Subscribe topic. The policy accomplishes that by making an HTTP POST request to http://localhost:3500/v1.0/publish/{{pubsub-name}}/{{topic}}, replacing template parameters and adding content specified in the policy statement.

The policy assumes that Dapr runtime is running in a sidecar container in the same pod as the gateway. Dapr runtime implements the Pub/Sub semantics. Learn more about Dapr integration with API Management.

Note

Set a policy's elements and child elements in the order provided in the policy statement. Learn more about how to set or edit API Management policies.

Policy statement

<publish-to-dapr pubsub-name="pubsub-name" topic="topic-name" ignore-error="false|true" response-variable-name="resp-var-name" timeout="in seconds" template="Liquid" content-type="application/json">
    <!-- message content -->
</publish-to-dapr>

Attributes

Attribute Description Required Default
pubsub-name The name of the target PubSub component. Maps to the pubsubname parameter in Dapr. If not present, the topic attribute value must be in the form of pubsub-name/topic-name. Policy expressions are allowed. No None
topic The name of the topic. Maps to the topic parameter in Dapr. Policy expressions are allowed. Yes N/A
ignore-error If set to true, instructs the policy not to trigger "on-error" section upon receiving error from Dapr runtime. Policy expressions aren't allowed. No false
response-variable-name Name of the Variables collection entry to use for storing response from Dapr runtime. Policy expressions aren't allowed. No None
timeout Time (in seconds) to wait for Dapr runtime to respond. Can range from 1 to 240 seconds. Policy expressions are allowed. No 5
template Templating engine to use for transforming the message content. "Liquid" is the only supported value. No None
content-type Type of the message content. "application/json" is the only supported value. No None

Usage

Usage notes

Dapr support must be enabled in the self-hosted gateway.

Example

The following example demonstrates sending the body of the current request to the "new" topic of the "orders" Pub/Sub component. Response received from the Dapr runtime is stored in the "dapr-response" entry of the Variables collection in the context object.

If Dapr runtime can't locate the target topic, for example, and responds with an error, the "on-error" section is triggered. The response received from the Dapr runtime is returned to the caller verbatim. Otherwise, default 200 OK response is returned.

The "backend" section is empty and the request is not forwarded to the backend.

<policies>
     <inbound>
        <base />
        <publish-to-dapr
           pubsub-name="orders"
               topic="new"
               response-variable-name="dapr-response">
            @(context.Request.Body.As<string>())
        </publish-to-dapr>
    </inbound>
    <backend>
    </backend>
    <outbound>
        <base />
    </outbound>
    <on-error>
        <base />
        <return-response response-variable-name="pubsub-response" />
    </on-error>
</policies>

Next steps

For more information about working with policies, see: