def error_callback(carrier, error, callback):
"""
A wrapper for for use when returning errors to the calling Task.
The wrapper is mainly to provide OpenTracing boilerplate.
The carrier should be provided in the case where we don't have the
original span relating to the request. In that case we create a new
span to represent this error from the information provided in
carrier, which should be an OpenTracing Carrier. If we do have the
original span then carrier should be None, and the span should be
managed in the code calling this function.
We pass in the callback to be used by this function as it may be
called from something asynchronous like a timeout, where the
callback may have been stored in pending_requests rather than using
the callback wrapped in the closure of execute_task.
"""
scope = None
if carrier:
scope = opentracing.tracer.start_active_span(
operation_name="Task",
child_of=span_context("text_map", carrier, self.logger),
)
else:
scope = opentracing.tracer.scope_manager.active
with scope:
opentracing.tracer.active_span.set_tag("error", True)
opentracing.tracer.active_span.log_kv(
{
"event": error["errorType"],
"message": error["errorMessage"],
}
)
if callable(callback):
callback(error)
def handler(self, message):
print(self.getName() + " working")
print(message)
with opentracing.tracer.start_active_span(
operation_name=self.getName(),
child_of=span_context("text_map", message.properties,
self.logger),
tags={
"component": "workers",
"message_bus.destination": self.getName(),
"span.kind": "consumer",
"peer.address": "amqp://localhost:5672"
}) as scope:
# Create simple reply. In a real processor **** DO WORK HERE ****
reply = {"reply": self.getName() + " reply"}
"""
Create the response message by reusing the request note that this
approach retains the correlation_id, which is necessary. If a fresh
Message instance is created we would need to get the correlation_id
from the request Message and use that value in the response message.
"""
"""
Start an OpenTracing trace for the rpcmessage response.
https://opentracing.io/guides/python/tracers/ standard tags are from
https://opentracing.io/specification/conventions/
"""
with opentracing.tracer.start_active_span(
operation_name=self.getName(),
child_of=opentracing.tracer.active_span,
tags={
"component": "workers",
"message_bus.destination": message.reply_to,
"span.kind": "producer",
"peer.address": "amqp://localhost:5672"
}) as scope:
message.properties = inject_span("text_map", scope.span,
self.logger)
message.subject = message.reply_to
message.reply_to = None
message.body = json.dumps(reply)
self.producer.send(message)
message.acknowledge() # Acknowledges the original request
def aws_api_StartExecution():
"""
https://docs.aws.amazon.com/step-functions/latest/apireference/API_StartExecution.html
"""
# print(params)
state_machine_arn = params.get("stateMachineArn")
if not state_machine_arn:
self.logger.warning(
"RestAPI StartExecution: stateMachineArn must be specified"
)
return aws_error("MissingRequiredParameter"), 400
if not valid_state_machine_arn(state_machine_arn):
self.logger.warning(
"RestAPI StartExecution: {} is an invalid State Machine ARN"
.format(state_machine_arn))
return aws_error("InvalidArn"), 400
"""
If name isn't provided create one from a UUID. TODO names should
be unique within a 90 day period, at the moment there is no code
to check for uniqueness of provided names so client code that
doesn't honour this may currently succeed in this implementation
but fail if calling real AWS StepFunctions.
"""
name = params.get("name", str(uuid.uuid4()))
if not valid_name(name):
self.logger.warning(
"RestAPI StartExecution: {} is an invalid name".format(
name))
return aws_error("InvalidName"), 400
input = params.get("input", "{}")
"""
First check if the input length has exceeded the 262144 character
quota described in Stepfunction Quotas page.
https://docs.aws.amazon.com/step-functions/latest/dg/limits.html
"""
if len(input) > MAX_DATA_LENGTH:
self.logger.error(
"RestAPI StartExecution: input size for execution '{}' exceeds "
"the maximum number of characters service limit.".
format(name))
return aws_error("InvalidExecutionInput"), 400
try:
input = json.loads(input)
except TypeError as e:
self.logger.error(
"RestAPI StartExecution: Invalid input, {}".format(e))
return aws_error("InvalidExecutionInput"), 400
except ValueError as e:
self.logger.error(
"RestAPI StartExecution: input {} does not contain valid JSON"
.format(input))
return aws_error("InvalidExecutionInput"), 400
# Look up stateMachineArn
state_machine = self.asl_store.get_cached_view(
state_machine_arn)
if not state_machine:
self.logger.info(
"RestAPI StartExecution: State Machine {} does not exist"
.format(state_machine_arn))
return aws_error("StateMachineDoesNotExist"), 400
# Form executionArn from stateMachineArn and name
arn = parse_arn(state_machine_arn)
execution_arn = create_arn(
service="states",
region=arn.get("region", self.region),
account=arn["account"],
resource_type="execution",
resource=arn["resource"] + ":" + name,
)
with opentracing.tracer.start_active_span(
operation_name="StartExecution:ExecutionLaunching",
child_of=span_context("http_headers", request.headers,
self.logger),
tags={
"component": "rest_api",
"execution_arn": execution_arn
}) as scope:
"""
The application context is described in the AWS documentation:
https://docs.aws.amazon.com/step-functions/latest/dg/input-output-contextobject.html
"""
# https://stackoverflow.com/questions/8556398/generate-rfc-3339-timestamp-in-python
start_time = datetime.now(
timezone.utc).astimezone().isoformat()
context = {
"Tracer": inject_span("text_map", scope.span,
self.logger),
"Execution": {
"Id": execution_arn,
"Input": input,
"Name": name,
"RoleArn": state_machine.get("roleArn"),
"StartTime": start_time,
},
"State": {
"EnteredTime": start_time,
"Name": ""
}, # Start state
"StateMachine": {
"Id": state_machine_arn,
"Name": state_machine.get("name"),
},
}
event = {"data": input, "context": context}
"""
threadsafe=True is important here as the RestAPI runs in a
different thread to the main event_dispatcher loop.
"""
try:
self.event_dispatcher.publish(event,
threadsafe=True,
start_execution=True)
except:
message = (
"RestAPI StartExecution: Internal messaging "
"error, start message could not be published.")
self.logger.error(message)
return aws_error("InternalError", message), 500
resp = {
"executionArn": execution_arn,
"startDate": time.time()
}
return jsonify(resp), 200
def asl_service_states_startExecution():
"""
Service Integration to stepfunctions. Initially this is limited to
integrating with stepfunctions running on this local ASL Workflow
Engine, however it should be possible to integrate with *real* AWS
stepfunctions too in due course.
Up until September 2019 real AWS stepfunctions didn't have a direct
Service Integration to other stepfunctions and required a lambda to
do this, so be aware that many online examples likely illustrate the
use of a lambda as a proxy to the child stepfunction but this link
documents the new more direct service integration:
https://docs.aws.amazon.com/step-functions/latest/dg/connect-stepfunctions.html
The resource ARN should be of the form:
arn:aws:states:region:account-id:states:startExecution
The Task must have a Parameters field of the form:
"Parameters": {
"Input": "ChildStepFunctionInput",
"StateMachineArn": "ChildStateMachineArn",
"Name": "OptionalExecutionName"
},
if the execution Name is not specified in the Parameters a UUID will
be assigned by the service.
TODO: At the moment this integration only supports the direct
request/response stepfunction integration NOT the "run a job" (.sync)
or "wait for callback" (.waitForTaskToken) forms so at the moment
we can't yet wait for the child stepfunction to complete or wait
for a callback. To achieve this we *probably* need to poll
ListExecutions with statusFilter="SUCCEEDED" comparing the response
with our executionArn, which is mostly fairly straightforward but
becomes more involved in a clustered environment. The callback
integration might be slightly easier to implement as it shouldn't
need any polling but one oddity is that there doesn't seem to be
a stepfunctions integration for SendTaskSuccess (or SendTaskFailure
or SendTaskHeartbeat) as those are the APIs that relate to
triggering or cancelling a callback by implication there is no
direct mechanism yet for a child stepfunction to actually do the
callback other than proxying via a lambda. My guess is that this is
an accidental omission that was missed when implementing the
stepfunctions integration and will be added IDC.
"""
execution_name = parameters.get("Name", str(uuid.uuid4()))
state_machine_arn = parameters.get("StateMachineArn")
if not state_machine_arn:
message = "TaskDispatcher asl_service_states_startExecution: " \
"StateMachineArn must be specified"
error = {"errorType": "MissingRequiredParameter", "errorMessage": message}
error_callback(context.get("Tracer", {}), error, callback)
return
arn = parse_arn(state_machine_arn)
state_machine_name = arn["resource"]
execution_arn = create_arn(
service="states",
region=arn.get("region", "local"),
account=arn["account"],
resource_type="execution",
resource=state_machine_name + ":" + execution_name,
)
# Look up stateMachineArn
state_machine = self.state_engine.asl_store.get_cached_view(state_machine_arn)
if not state_machine:
message = "TaskDispatcher asl_service_states_startExecution: " \
"State Machine {} does not exist".format(
state_machine_arn
)
error = {"errorType": "StateMachineDoesNotExist", "errorMessage": message}
error_callback(context.get("Tracer", {}), error, callback)
return
"""
Start an OpenTracing trace for the child StartExecution request.
https://opentracing.io/guides/python/tracers/ standard tags are from
https://opentracing.io/specification/conventions/
"""
with opentracing.tracer.start_active_span(
operation_name="Task",
child_of=span_context("text_map", context.get("Tracer", {}), self.logger),
tags={
"component": "task_dispatcher",
"resource_arn": resource_arn,
"execution_arn": context["Execution"]["Id"],
"child_execution_arn": execution_arn,
}
) as scope:
# Create the execution context and the event to publish to launch
# the requested new state machine execution.
# https://stackoverflow.com/questions/8556398/generate-rfc-3339-timestamp-in-python
start_time = datetime.now(timezone.utc).astimezone().isoformat()
child_context = {
"Tracer": inject_span("text_map", scope.span, self.logger),
"Execution": {
"Id": execution_arn,
"Input": parameters.get("Input", {}),
"Name": execution_name,
"RoleArn": state_machine.get("roleArn"),
"StartTime": start_time,
},
"State": {"EnteredTime": start_time, "Name": ""}, # Start state
"StateMachine": {"Id": state_machine_arn, "Name": state_machine_name},
}
event = {"data": parameters.get("Input", {}), "context": child_context}
self.state_engine.event_dispatcher.publish(
event, start_execution=True
)
"""
The Stepfunction metrics specified in the docs:
https://docs.aws.amazon.com/step-functions/latest/dg/procedure-cw-metrics.html
describe Service Integration Metrics, which would include child
Stepfunctions. The "dimension" for these, however is the
resource ARN of the integrated service. In practice that is
less than ideal as it only really describes the startExecution
service so the ARN is the same irrespective of the state machine.
"""
if self.task_metrics:
self.task_metrics["ServiceIntegrationsScheduled"].inc(
{"ServiceIntegrationResourceArn": resource_arn}
)
result = {"executionArn": execution_arn, "startDate": time.time()}
"""
For now we only support "fire and forget" launching of child
Stepfunctions and *not* synchronous ones that wait for the
child Stepfunction to complete nor waitForTaskToken style
callbacks. As it it fire and forget the ServiceIntegration
is deemed successful if the request is successfully dispatched.
TODO the other ServiceIntegration metrics are really only useful
for synchronous (not fire and forget) execution invocations.
"""
if self.task_metrics:
self.task_metrics["ServiceIntegrationsSucceeded"].inc(
{"ServiceIntegrationResourceArn": resource_arn}
)
callback(result)
def asl_service_rpcmessage():
"""
Publish message to the required rpcmessage worker resource. The
message body is a JSON string containing the "effective parameters"
passed from the StateEngine and the message subject is the resource
name, which in turn maps to the name of the queue that the resource
has set up to listen on. In order to ensure that responses from
Task resources return to the correct calling Task the message is
populated with a reply to address representing this this workflow
engine's reply_to queue as well as a correlation ID to ensure that
response messages can be correctly tracked irrespective of the order
that they are returned - as that might be quite different from the
order that the requests were sent.
Setting content_type to application/json isn't necessary for correct
operation, however it is the correct thing to do:
https://www.ietf.org/rfc/rfc4627.txt.
"""
# print("asl_service_rpcmessage")
# print(service)
# print(resource_type)
# print(resource)
# print(parameters)
# TODO deal with the case of delivering to a different broker.
# Associate response callback with this request via correlation ID
correlation_id = str(uuid.uuid4())
"""
Create a timeout in case the rpcmessage invocation fails.
The timeout sends an error response to the calling Task state and
deletes the pending request.
"""
def on_timeout():
# Do lookup in case timeout fires after a successful response.
request = self.pending_requests.get(correlation_id)
if request:
del self.pending_requests[correlation_id]
callback, resource_arn, sched_time, timeout_id, task_span = request
error = {
"errorType": "States.Timeout",
"errorMessage": "State or Execution ran for longer " +
"than the specified TimeoutSeconds value",
}
with opentracing.tracer.scope_manager.activate(
span=task_span,
finish_on_close=True
) as scope:
error_callback(None, error, callback)
"""
Start an OpenTracing trace for the rpcmessage request.
https://opentracing.io/guides/python/tracers/ standard tags are from
https://opentracing.io/specification/conventions/
"""
with opentracing.tracer.start_active_span(
operation_name="Task",
child_of=span_context("text_map", context.get("Tracer", {}), self.logger),
tags={
"component": "task_dispatcher",
"resource_arn": resource_arn,
"message_bus.destination": resource,
"span.kind": "producer",
"peer.address": self.peer_address,
"execution_arn": context["Execution"]["Id"]
},
finish_on_close=False
) as scope:
"""
We also pass the span to pending_requests so we can use
it when receiving a response, and in case of a timeout.
"""
carrier = inject_span("text_map", scope.span, self.logger)
message = Message(
json.dumps(parameters),
properties=carrier,
content_type="application/json",
subject=resource,
reply_to=self.reply_to.name,
correlation_id=correlation_id,
# Give the RPC Message a TTL equivalent to the ASL
# Task State (or Execution) timeout period. Both are ms.
expiration=timeout,
)
timeout_id = self.state_engine.event_dispatcher.set_timeout(
on_timeout, timeout
)
"""
The service response message is handled by handle_rpcmessage_response()
If the response occurs before the timeout expires the timeout
should be cancelled, so we store the timeout_id as well as the
required callback in the dict keyed by correlation_id.
As mentioned above we also store the OpenTracing span so that if a
timeout occurs we can raise an error on the request span.
"""
self.pending_requests[correlation_id] = (
callback, resource_arn, time.time() * 1000, timeout_id, scope.span
)
self.producer.send(message)
if self.task_metrics:
self.task_metrics["LambdaFunctionsScheduled"].inc(
{"LambdaFunctionArn": resource_arn}
)
def handle_rpcmessage_response(self, message):
"""
This is a message listener receiving messages from the reply_to queue
for this workflow engine instance.
TODO cater for the case where requests are sent but responses never
arrive, this scenario will cause self.pending_requests to "leak" as
correlation_id keys get added but not removed. This situation should be
improved as we add code to handle Task state "rainy day" scenarios such
as Timeouts etc. so park for now, but something to be aware of.
"""
correlation_id = message.correlation_id
request = self.pending_requests.get(correlation_id)
if request:
try:
del self.pending_requests[correlation_id]
callback, resource_arn, sched_time, timeout_id, rpcmessage_task_span = request
with opentracing.tracer.scope_manager.activate(
span=rpcmessage_task_span,
finish_on_close=True
) as scope:
# Cancel the timeout previously set for this request.
self.state_engine.event_dispatcher.clear_timeout(timeout_id)
if callable(callback):
message_body = message.body
"""
First check if the response has exceeded the 262144
character quota described in Stepfunction Quotas page.
https://docs.aws.amazon.com/step-functions/latest/dg/limits.html
We do the test here as we have the raw JSON string handy.
"""
if len(message_body) > MAX_DATA_LENGTH:
result = {"errorType": "States.DataLimitExceeded"}
else:
result = json.loads(message_body.decode("utf8"))
error_type = result.get("errorType")
if error_type:
opentracing.tracer.active_span.set_tag("error", True)
opentracing.tracer.active_span.log_kv(
{
"event": error_type,
"message": result.get("errorMessage", ""),
}
)
if self.task_metrics:
"""
When Lambda times out it returns JSON including
"errorType": "TimeoutError"
See the following for an example illustration
https://stackoverflow.com/questions/65036533/my-lambda-is-throwing-a-invoke-error-timeout
rpcmessage processors should follow the same
convention so we can trap processor timeout
errors and provide metrics on these.
"""
if error_type == "TimeoutError":
self.task_metrics["LambdaFunctionsTimedOut"].inc(
{"LambdaFunctionArn": resource_arn}
)
self.task_metrics["LambdaFunctionsFailed"].inc(
{"LambdaFunctionArn": resource_arn}
)
else:
if self.task_metrics:
self.task_metrics["LambdaFunctionsSucceeded"].inc(
{"LambdaFunctionArn": resource_arn}
)
if self.task_metrics:
duration = (time.time() * 1000.0) - sched_time
self.task_metrics["LambdaFunctionTime"].observe(
{"LambdaFunctionArn": resource_arn}, duration
)
callback(result)
except ValueError as e:
self.logger.error(
"Response {} does not contain valid JSON".format(message.body)
)
else:
with opentracing.tracer.start_active_span(
operation_name="Task",
child_of=span_context("text_map", message.properties, self.logger),
tags={
"component": "task_dispatcher",
"message_bus.destination": self.reply_to.name,
"span.kind": "consumer",
"peer.address": self.peer_address
}
) as scope:
self.logger.info("Response {} has no matching requestor".format(message))
scope.span.set_tag("error", True)
scope.span.log_kv(
{
"event": "No matching requestor",
"message": "Response has no matching requestor",
}
)
message.acknowledge(multiple=False)
