echostream-node 0.3.8

EchoStream library for implementing remote nodes

echostream-node

EchoStream library for implementing remote nodes that can be used in the echostream system.

This package supports creating External Nodes and Managed Node Types, and supports the following EchoStream use cases:

• An External Node in an External App or Cross Account App that is a stand-alone application or part of another application, using either threading or asyncio.
• An External Node in a Cross Account App that is an AWS Lambda function. This use case only supports threading.
• A Managed Node Type, using either threading or asyncio

Installation

Python

pip install echostream-node

AWS Lambda

You may use the publiclally provided layer instead of directly installing echostream-node in your lambda package. This layer includes echostream-node and all of the Python dependencies except those built-in to the AWS Lambda environment for Python.

The Layer arn is:

arn:aws:lambda:{region}:226390263822:layer:echostream-node-{version}:1

where {version} is the version of echostream-node that you want, with . replaced with _ and {region} is the AWS region that your Lambda will run in. Currently, us-east-1, us-east-2, us-west-1 and us-west-2 are supported.

For example, for echostream-node==0.3.7 in the us-east-1 region the layer arn would be:

arn:aws:lambda:us-east-1:226390263822:layer:echostream-node-0_3_7:1

Usage

Configuration

To instantiate a Node a number of variables are required. These can be provided either as environment variables or directly on Node creation:

Parameter	Environment Variable	Description
appsync_endpoint	APPSYNC_ENDPOINT	The URL to the EchoStream API endpoint.
client_id	CLIENT_ID	The Application Client ID for the App's Cognito Client Application.
name	NODE	The Node's name.
password	PASSWORD	The password for the App User for the Node's App.
tenant	TENANT	The name of the Tenant that the Node is a part of.
username	USER_NAME	The name of the App User for the Node's App.
user_pool_id	USER_POOL_ID	The User Pool Id for the App's Cognito User Pool.

Threading Application Node

from signal import SIGHUP, SIGINT, SIGTERM, signal, strsignal

from echostream_node import Message
from echostream_node.threading import AppNode


class MyExternalNode(AppNode):

    def handle_received_message(self, *, message: Message, source: str) -> None:
        print(f"Got a message:\n{message.body}")
        self.audit_message(message, source=source)
        
    def signal_handler(self, signum: int, _: object) -> None:
        print(f"{strsignal(signum)} received, shutting down")
        self.stop()

    def start(self) -> None:
        super().start()
        signal(SIGHUP, self.signal_handler)
        signal(SIGINT, self.signal_handler)
        signal(SIGTERM, self.signal_handler)

try:
    my_external_node = MyExternalNode()
    my_external_node.start()
    for i in range(100):
        message = my_external_node.create_message(str(i))
        my_external_node.send_message(message)
        my_external_node.audit_message(message)
    my_external_node.join()
except Exception:
    print("Error running node")

Asyncio Application Node

import asyncio

import aiorun
from echostream_node import Message
from echostream_node.asyncio import Node

class MyExternalNode(Node):

    async def handle_received_message(self, *, message: Message, source: str) -> None:
        print(f"Got a message:\n{message.body}")
        self.audit_message(message, source=source)


async def main(node: Node) -> None:
    try:
        await node.start()
        for i in range(100):
            message = my_external_node.create_message(str(i))
            my_external_node.send_message(message)
            my_external_node.audit_message(message)
        await node.join()
    except asyncio.CancelledError:
        pass
    except Exception:
        print("Error running node")


if __name__ == "__main__":
    aiorun.run(main(MyExternalNode()), stop_on_unhandled_errors=True, use_uvloop=True)

Cross Account Lambda Node

from echostream_node import Message
from echostream_node.threading import LambdaNode

class MyExternalNode(LambdaNode):
    def handle_received_message(self, *, message: Message, source: str) -> None:
        print(f"Got a message:\n{message.body}")
        self.audit_message(message, source=source)
        
MY_EXTERNAL_NODE = MyExternalNode()

def lambda_handler(event, context):
    MY_EXTERNAL_NODE.handle_event(event)

Concurrent vs Sequential Message Processing

By default, all Nodes created using the package will process messages sequentially. This is normally the behavior that you want, as many messaging protocols require guaranteed ordering and therefore sequential processing within your Nodes. If this is the behavior that you require, nothign special is needed to gain it from echostream-node.

However, there are use cases where message ordering is not important but processing speed is. In these cases, you may configure your Node upon creation to concurrently process the messages that it receives.

Making a Threading Application Node Concurrent

If your Node inherits from the echostream_node.threading.AppNode class you can achieve concurrency using threading.

This will create an AppNode that uses the provided ThreadPoolExecutor to concurrently process received Messages. Note that while you can set the maximum number of workers to less than 10, there is no gain to setting it to more than 10 since Nodes will only process up to 10 messages at a time.

from concurrent.futures import ThreadPoolExecutor

from echostream_node import Message
from echostream_node.threading import AppNode

class MyExternalNode(AppNode):

    def __init__(self) -> None:
        super().__init__(executor=ThreadPoolExecutor(max_workers=10))

    def handle_received_message(self, *, message: Message, source: str) -> None:
        print(f"Got a message:\n{message.body}")
        self.audit_message(message, source=source)

Making a Asyncio Application Node Concurrent

If your Node inherits from the echostream_node.asyncio.Node you can set the Node to process incoming Messages concurrently. There is no setting for the maximum number of tasks; a task is created per received Message.

import asyncio

from echostream_node import Message
from echostream_node.asyncio import Node

class MyExternalNode(Node):

    def __init__(self) -> None:
        super().__init__(concurrent_processing=True)

    async def handle_received_message(self, *, message: Message, source: str) -> None:
        print(f"Got a message:\n{message.body}")
        self.audit_message(message, source=source)

Making a Lambda Node Concurrent

The AWS Lambda platform does not support shared memory, and therefore will only support concurrency via threading. This will create a LambdaNode that uses an optimized (to your Lambda function's resources) ThreadPoolExecutor to concurrently process received Messages.

from echostream_node import Message
from echostream_node.threading import LambdaNode

class MyExternalNode(LambdaNode):

    def __init__(self) -> None:
        super().__init__(concurrent_processing=True)

    def handle_received_message(self, *, message: Message, source: str) -> None:
        print(f"Got a message:\n{message.body}")
        self.audit_message(message, source=source)

Lambda Nodes and Partial Success Reporting

When you connect an Edge's SQS Queue to the AWS Lambda function implementing your Lambda Node, you can choose to Report Batch Item Failures. This allows your Lambda Node to report partial success back to the SQS Queue, but it does require that your Lambda Node operate differently.

If you wish to take advantage of this, set report_batch_item_failures when you create your Lambda Node. This can be set even if your Node is not concurrent processing.

from echostream_node import Message
from echostream_node.threading import LambdaNode

class MyExternalNode(LambdaNode):

    def __init__(self) -> None:
        super().__init__(report_batch_item_failures=True)

    def handle_received_message(self, *, message: Message, source: str) -> None:
        print(f"Got a message:\n{message.body}")
        self.audit_message(message, source=source)

Full documentation may be found at https://docs.echostream-node.echo.stream.