AWS Lambda event handler manager
Project description
Domovoi is an extension to AWS Chalice to handle AWS Lambda event sources other than HTTP requests through API Gateway. Domovoi lets you easily configure and deploy a Lambda function to run on a schedule or in response to a variety of events like an SNS push notification, S3 event, or custom state machine transition:
import json, boto3, domovoi
app = domovoi.Domovoi()
@app.scheduled_function("cron(0 18 ? * MON-FRI *)")
def foo(event, context):
context.log("foo invoked at 06:00pm (UTC) every Mon-Fri")
return dict(result=True)
@app.scheduled_function("rate(1 minute)")
def bar(event, context):
context.log("bar invoked once a minute")
boto3.resource("sns").create_topic(Name="bartender").publish(Message=json.dumps({"beer": 1}))
return dict(result="Work work work")
@app.sns_topic_subscriber("bartender")
def tend(event, context):
message = json.loads(event["Records"][0]["Sns"]["Message"])
context.log(dict(beer="Quadrupel", quantity=message["beer"]))
@app.cloudwatch_event_handler(source=["aws.ecs"])
def monitor_ecs_events(event, context):
message = json.loads(event["Records"][0]["Sns"]["Message"])
context.log("Got an event from ECS: {}".format(message))
@app.s3_event_handler(bucket="myS3bucket", events=["s3:ObjectCreated:*"], prefix="foo", suffix=".bar")
def monitor_s3(event, context):
message = json.loads(event["Records"][0]["Sns"]["Message"])
context.log("Got an event from S3: {}".format(message))
# Set use_sns=False to subscribe your Lambda directly to S3 events without forwrading them through an SNS topic.
# That approach has fewer moving parts, but you can only subscribe one Lambda function to events in a given S3 bucket.
@app.s3_event_handler(bucket="myS3bucket", events=["s3:ObjectCreated:*"], prefix="foo", suffix=".bar", use_sns=False)
def monitor_s3(event, context):
message = json.loads(event["Records"][0]["Sns"]["Message"])
context.log("Got an event from S3: {}".format(message))
# DynamoDB event format: https://docs.aws.amazon.com/lambda/latest/dg/eventsources.html#eventsources-ddb-update
@app.dynamodb_stream_handler(table_name="MyDynamoTable", batch_size=200)
def handle_dynamodb_stream(event, context):
context.log("Got {} events from DynamoDB".format(len(event["Records"])))
context.log("First event: {}".format(event["Records"][0]["dynamodb"]))
# Use the following command to log a CloudWatch Logs message that will trigger this handler:
# python -c'import watchtower as w, logging as l; L=l.getLogger(); L.addHandler(w.CloudWatchLogHandler()); L.error(dict(x=8))'
# See http://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/FilterAndPatternSyntax.html for the filter pattern syntax
@app.cloudwatch_logs_sub_filter_handler(log_group_name="watchtower", filter_pattern="{$.x = 8}")
def monitor_cloudwatch_logs(event, context):
print("Got a CWL subscription filter event:", event)
# See http://docs.aws.amazon.com/step-functions/latest/dg/concepts-amazon-states-language.html
# See the "AWS Step Functions state machines" section below for a complete example of setting up a state machine.
@app.step_function_task(state_name="Worker", state_machine_definition=state_machine)
def worker(event, context):
return {"result": event["input"] + 1, "my_state": context.stepfunctions_task_name}Installation
pip install domovoi
Usage
First-time setup:
domovoi new-project
Edit the Domovoi app entry point in app.py using examples above.
Edit the IAM policy for your Lambda function in my_project/.chalice/policy-dev.json to add any permissions it needs.
Deploy the event handlers:
domovoi deploy
To stage files into the deployment package, use a domovoilib directory in your project where you would use chalicelib in Chalice. For example, my_project/domovoilib/rds_cert.pem becomes /var/task/domovoilib/rds_cert.pem with your function executing in /var/task/app.py with /var/task as the working directory. See the Chalice docs for more information on how to set up Chalice configuration.
Supported event types
See Supported Event Sources for an overview of event sources that can be used to trigger Lambda functions. Domovoi supports the following event sources:
CloudWatch Events rule targets, including CloudWatch Scheduled Events (see CloudWatch Events Event Examples for a list of event types supported by CloudWatch Events)
AWS Step Functions state machine tasks
Possible future event sources to support:
Kinesis stream events
SES (email) events
AWS Step Functions state machines
Domovoi supports AWS Lambda integration with AWS Step Functions. Step Functions state machines can be started using the StartExecution method or the API Gateway Step Functions integration.
See the domovoi/examples directory for examples of Domovoi app.py apps using a state machine, including a loop that restarts the Lambda when it’s about to hit its execution time limit, and a threadpool pattern that divides work between multiple Lambdas.
When creating a Step Functions State Machine driven Domovoi daemon Lambda, the State Machine assumes the same IAM role as the Lambda itself. To allow the State Machine to invoke the Lambda, edit the IAM policy (under your app directory, in .chalice/policy-dev.json) to include a statement allowing the “lambda:InvokeFunction” action on all resources, or on the ARN of the Lambda itself.
Configuration
Dead Letter Queues
To enable your Lambda function to forward failed invocation notifications to dead letter queuees, set the configuration key dead_letter_queue_target_arn in the file .chalice/config.json to the target DLQ ARN. For example:
{
"app_name": "my_app",
...
"dead_letter_queue_target_arn": "arn:aws:sns:us-east-1:123456789012:my-dlq"
}
You may need to update your Lambda IAM policy (.chalice/policy-dev.json) to give your Lambda access to SNS or SQS.
Concurrency Reservations
For high volume Lambda invocations in accounts with multiple Lambdas, you may need to set per-function concurrency limits to partition the overall concurrency quota and prevent one set of Lambdas from overloading another. In Domovoi, you can do so by setting the configuration key reserved_concurrent_executions in the file .chalice/config.json to the desired concurrency reservation. For example:
{
"app_name": "my_app",
...
"reserved_concurrent_executions": 500
}
Links
Bugs
Please report bugs, issues, feature requests, etc. on GitHub.
License
Licensed under the terms of the Apache License, Version 2.0.
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