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Tutorial: Anomaly Detection

You will learn how to build a simple anomaly detection system, a common use case of stateful streaming applications. This will show how to use a Quix Streams application to:

  • Create a topic
  • Use stateful windowed operations
  • Do simple event alterations
  • Do simple event filtering
  • Produce the result to a topic

Outline of the Problem

For our example, we have "machines" performing various tasks. While running, they emit their current temperature several times a second, which we can use to detect issues.

The machines typically rise and fall in temperature under normal use, but having a "prolonged" temperature above 90C is considered malfunctioning.

When this occurs, we want to send alerts as soon as possible so appropriate actions can be taken.

Our Example

We will use a producer to generate mock temperature events for 3 machines (MACHINE_IDs '0', '1', or '2'); ID's 0 and 1 are functioning normally, 2 is malfunctioning (overheating).

These events will be processed by our new Anomaly Detector application.

NOTE: our example uses JSON formatting for Kafka message values.

Alerting Approach (Windowing)

First, let's do an overview of the alerting approach we'll take with our Anomaly Detector.

Basically, we want to look at temperatures for a given MACHINE_ID over a shifting window of time (and as close to "now" as possible) and see if the mean temperature in that window surpasses our allowed threshold of 90C.

This approach is desirable since temperatures fluctuate quickly; it enables more accurate alerting since it: - is more tolerant to erroneous sensor readings/spikes - allows more time for the machine to cool back down (as part of normal operation)

Before Getting Started

  • You will see links scattered throughout this tutorial.
    • Tutorial code links are marked >>> LIKE THIS <<< .
    • All other links provided are completely optional.
    • They are great ways to learn more about various concepts if you need it!

Generating Temperature Data

Without going into much detail, we have this >>> Temperature Readings Producer <<< to pair up nicely with our Anomaly Detector.

It cycles through MACHINE_ID's 0-2 (using the ID as the Kafka key), and produces a (-1, 0, +1) temperature change for each machine a few times a second, along with the time.

So the kafka messages look like:

# ...
{kafka_key: '0', kafka_value: {"Temperature_C": 65, "Timestamp": 1710856626905833677}}
{kafka_key: '1', kafka_value: {"Temperature_C": 48, "Timestamp": 1710856627107115587}}
{kafka_key: '2', kafka_value: {"Temperature_C": 82, "Timestamp": 1710856627307969878}}
{kafka_key: '0', kafka_value: {"Temperature_C": 65, "Timestamp": 1710856627508888818}} # +0 C
{kafka_key: '1', kafka_value: {"Temperature_C": 49, "Timestamp": 1710856627710089041}} # +1 C
{kafka_key: '2', kafka_value: {"Temperature_C": 81, "Timestamp": 1710856627910952220}} # -1 C
# etc...

It stops producing data when MACHINE_ID 2 hits a temperature of 100C, which should collectively cause at least one alert in our downstream Anomaly Detector.

Feel free to inspect it further, but it's just to get some data flowing. Our focus is on the Anomaly Detector itself.

Anomaly Detector Application

Now let's go over our >>> Anomaly Detector Application <<< line-by-line!

Create Application

app = Application(
    broker_address=os.environ.get("BROKER_ADDRESS", "localhost:9092"),
    consumer_group="temperature_alerter",
    auto_offset_reset="earliest"
)

First, create the Quix Streams Application, which is our constructor for everything! We provide it our connection settings, consumer group (ideally unique per Application), and where the consumer group should start from on our topic.

NOTE: Once you are more familiar with Kafka, we recommend learning more about auto_offset_reset.

Define Topics

temperature_readings_topic = app.topic(name="temperature_readings")
alerts_topic = app.topic(name="alerts")

Next we define our input/output topics, named temperature_readings_topic and alerts_topic, respectively.

They each return Topic objects, used later on.

NOTE: the topics will automatically be created for you in Kafka when you run the application should they not exist.

The StreamingDataFrame (SDF)

sdf = app.dataframe(topic=temperature_readings_topic)

Now for the fun part: building our StreamingDataFrame, often shorthanded to "SDF".

SDF allows manipulating the message value in a dataframe-like fashion using various operations.

After initializing, we continue re-assigning to the same sdf variable as we add operations.

(Also: notice that we pass our input Topic from the previous step to it.)

Prep Data for Windowing

sdf = sdf.apply(lambda data: data["Temperature_C"])

To use the built-in windowing functions, our incoming event needs to be transformed: at this point the unaltered event dictionary will look something like (and this should be familiar!):

>>> {"Temperature_C": 65, "Timestamp": 1710856626905833677}

But it needs to be just the temperature:

>>> 65

So we'll perform a generic SDF transformation using SDF.apply(F), (F should take your current message value as an argument, and return your new message value): our F is a simple lambda, in this case.

Windowing

sdf = sdf.hopping_window(duration_ms=5000, step_ms=1000).mean().current()

Now we do a (5 second) windowing operation on our temperature value. A few very important notes here:

  • You can use either a "current" or "final" window emission. "Current" is often preferred for an "alerting" style.

  • Window calculations relate specifically to its message key.

    • Since we care about temperature readings PER MACHINE, our example producer used MACHINE_ID as the Kafka message key.
    • If we had instead used a static key, say "my_machines", our Anomaly Detector would have evaluated the machines together as one.
  • The event's windowing timestamp comes from the "Timestamp" (case-sensitive!!!) field, which SDF looks for in the message value when first receiving it. If it doesn't exist, the kafka message timestamp is used. A custom function can also be used.

Using Window Result

def should_alert(window_value):
    if window_value >= 90:
        print(f'Alerting for MID {message_key()}: Average Temperature {window_value}')
        return True

sdf = sdf.apply(lambda result: round(result['value'], 2)).filter(should_alert)

Now we get a window result (mean) along with its start/end timestamp:

>>> {"value": 67.49478585, "start": 1234567890, "end": 1234567895}

We don't particularly care about the window itself in our case, just the result...so we extract the "value" with SDF.apply() and SDF.filter(F), where F is our "should_alert" function.

For SDF.filter(F), if the (boolean-ed) return value of F is: - True -> continue processing this event - False -> stop ALL further processing of this event (including produces!)

In our case, this example event would then stop since bool(None) is False.

Producing an Alert

sdf = sdf.to_topic(alerts_topic)

However, if the value ended up >= 90....we finally finish by producing our alert to our downstream topic via SDF.to_topic(T), where T is our previously defined Topic (not the topic name!).

NOTE: because we use "Current" windowing, we may produce a lot of "duplicate" alerts once triggered...you could solve this in numerous ways downstream. What we care about is alerting as soon as possible!

Try it yourself!

1. Run Kafka

First, have a running Kafka cluster.

To conveniently follow along with this tutorial, just run this simple one-liner.

2. Install Quix Streams

In your python environment, run pip install quixstreams

3. Run the Producer and Application

Just call python producer.py and python application.py in separate windows.

You'll note that the Application does not print any output beyond initialization: it will only print alerts being fired (and thus when it's producing a downstream message).

4. Check out the results!

Eventually, you should see an alert will look something like:

>>> Alerting for MID b'2': Average Temperature 98.57

NICE!