# Bindings Dapr provides bi-directional binding capabilities for applications and a consistent approach to interacting with different cloud/on-premise services or systems. Developers can invoke output bindings using the Dapr API, and have the Dapr runtime trigger an application with input bindings. Examples for bindings include ```Kafka```, ```Rabbit MQ```, ```Azure Event Hubs```, ```AWS SQS```, ```GCP Storage``` to name a few. ## Contents - [Bindings Structure](#bindings-structure) - [Invoking Service Code Through Input Bindings](#invoking-service-code-through-input-bindings) - [Sending Messages to Output Bindings](#sending-messages-to-output-bindings) ## Bindings Structure A Dapr Binding yaml file has the following structure: ```yaml apiVersion: dapr.io/v1alpha1 kind: Component metadata: name: namespace: spec: type: bindings. metadata: - name: value: ``` The ```metadata.name``` is the name of the binding. If running self hosted locally, place this file in your `components` folder next to your state store and message queue yml configurations. If running on kubernetes apply the component to your cluster. > **Note:** In production never place passwords or secrets within Dapr component files. For information on securely storing and retrieving secrets using secret stores refer to [Setup Secret Store](../../howto/setup-secret-store) ## Invoking Service Code Through Input Bindings A developer who wants to trigger their app using an input binding can listen on a ```POST``` http endpoint with the route name being the same as ```metadata.name```. On startup Dapr sends a ```OPTIONS``` request to the ```metadata.name``` endpoint and expects a different status code as ```NOT FOUND (404)``` if this application wants to subscribe to the binding. The ```metadata``` section is an open key/value metadata pair that allows a binding to define connection properties, as well as custom properties unique to the component implementation. ### Examples For example, here's how a Python application subscribes for events from ```Kafka``` using a Dapr API compliant platform. Note how the metadata.name value `kafkaevent` in the components matches the POST route name in the Python code. #### Kafka Component ```yaml apiVersion: dapr.io/v1alpha1 kind: Component metadata: name: kafkaevent namespace: default spec: type: bindings.kafka metadata: - name: brokers value: "http://localhost:5050" - name: topics value: "someTopic" - name: publishTopic value: "someTopic2" - name: consumerGroup value: "group1" ``` #### Python Code ```python from flask import Flask app = Flask(__name__) @app.route("/kafkaevent", methods=['POST']) def incoming(): print("Hello from Kafka!", flush=True) return "Kafka Event Processed!" ``` ### Binding endpoints Bindings are discovered from component yaml files. Dapr calls this endpoint on startup to ensure that app can handle this call. If the app doesn't have the endpoint, Dapr ignores it. #### HTTP Request ```http OPTIONS http://localhost:/ ``` #### HTTP Response codes Code | Description ---- | ----------- 404 | Application does not want to bind to the binding all others | Application wants to bind to the binding #### URL Parameters Parameter | Description --------- | ----------- appPort | the application port name | the name of the binding ### Binding payload In order to deliver binding inputs, a POST call is made to user code with the name of the binding as the URL path. #### HTTP Request ```http POST http://localhost:/ ``` #### HTTP Response codes Code | Description ---- | ----------- 200 | Application processed the input binding successfully #### URL Parameters Parameter | Description --------- | ----------- appPort | the application port name | the name of the binding #### HTTP Response body (optional) Optionally, a response body can be used to directly bind input bindings with state stores or output bindings. **Example:** Dapr stores ```stateDataToStore``` into a state store named "stateStore". Dapr sends ```jsonObject``` to the output bindings named "storage" and "queue" in parallel. If ```concurrency``` is not set, it is sent out sequential (the example below shows these operations are done in parallel) ```json { "storeName": "stateStore", "state": stateDataToStore, "to": ['storage', 'queue'], "concurrency": "parallel", "data": jsonObject, } ``` ## Invoking Output Bindings This endpoint lets you invoke a Dapr output binding. Dapr bindings support various operations, such as `create`. See the [different specs](../specs/bindings) on each binding to see the list of supported operations. ### HTTP Request ```http POST/PUT http://localhost:/v1.0/bindings/ ``` ### HTTP Response codes Code | Description ---- | ----------- 200 | Request successful 500 | Request failed ### Payload The bindings endpoint receives the following JSON payload: ```json { "data": "", "metadata": { "": "" }, "operation": "" } ``` The `data` field takes any JSON serializable value and acts as the payload to be sent to the output binding. The `metadata` field is an array of key/value pairs and allows you to set binding specific metadata for each call. The `operation` field tells the Dapr binding which operation it should perform. ### URL Parameters Parameter | Description --------- | ----------- daprPort | the Dapr port name | the name of the output binding to invoke ### Examples ```shell curl -X POST http://localhost:3500/v1.0/bindings/myKafka \ -H "Content-Type: application/json" \ -d '{ "data": { "message": "Hi" }, "metadata": { "key": "redis-key-1" }, "operation": "create" }' ``` ### Common metadata values There are common metadata properties which are support accross multiple binding components. The list below illustrates them: |Property|Description|Binding definition|Available in |-|-|-|-| |ttlInSeconds|Defines the time to live in seconds for the message|If set in the binding definition will cause all messages to have a default time to live. The message ttl overrides any value in the binding definition.|RabbitMQ, Azure Service Bus, Azure Storage Queue|