Bindings API reference
Detailed documentation on the bindings API
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.
Bindings Structure
A Dapr Binding yaml file has the following structure:
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
name: <NAME>
namespace: <NAMESPACE>
spec:
type: bindings.<TYPE>
metadata:
- name: <NAME>
value: <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
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
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
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
OPTIONS http://localhost:<appPort>/<name>
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 |
Note, all URL parameters are case-sensitive.
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
POST http://localhost:<appPort>/<name>
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 |
Note, all URL parameters are case-sensitive.
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)
{
"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 on each binding to see the list of supported operations.
HTTP Request
POST/PUT http://localhost:<daprPort>/v1.0/bindings/<name>
HTTP Response codes
Code | Description |
---|---|
200 | Request successful |
500 | Request failed |
Payload
The bindings endpoint receives the following JSON payload:
{
"data": "",
"metadata": {
"": ""
},
"operation": ""
}
Note, all URL parameters are case-sensitive.
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 |
Note, all URL parameters are case-sensitive.
Examples
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 across 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 |
Last modified February 16, 2021: Merge pull request #1235 from dapr/update-v0.11 (b4e9fbb)