Amazon Glue interactive sessions for streaming - Amazon Glue
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Amazon Glue interactive sessions for streaming

Switching streaming session type

Use the Amazon Glue interactive sessions configuration magic, %streaming, to define the job you are running and initialize a streaming interactive session.

Sampling input stream for interactive development

One tool we have derived to help enhance the interactive experience in Amazon Glue interactive sessions is the addition of a new method under GlueContext to obtain a snapshot of a stream in a static DynamicFrame. GlueContext allows you to inspect, interact and implement your workflow.

With the GlueContext class instance, you will be able to locate the method getSampleStreamingDynamicFrame. Required arguments for this method are:

  • dataFrame: The Spark Streaming DataFrame

  • options: See available options below

Available options include:

  • windowSize: This is also called Microbatch Duration. This parameter will determine how long a streaming query will wait after previous batch was triggered. This parameter value must be smaller than pollingTimeInMs.

  • pollingTimeInMs: The total length of time the method will run. It will fire off at least one micro batch to obtain sample records from the input stream.

  • recordPollingLimit: This parameter helps you limit the total number of records you will poll from the stream.

  • (Optional) You can also use writeStreamFunction to apply this custom function to every record sampling function. See below for examples in Scala and Python.

val sampleBatchFunction = (batchDF: DataFrame, batchId: Long) => {//Optional but you can replace your own forEachBatch function here} val jsonString: String = s"""{"pollingTimeInMs": "10000", "windowSize": "5 seconds"}""" val dynFrame = glueContext.getSampleStreamingDynamicFrame(YOUR_STREAMING_DF, JsonOptions(jsonString), sampleBatchFunction)
def sample_batch_function(batch_df, batch_id): //Optional but you can replace your own forEachBatch function here options = { "pollingTimeInMs": "10000", "windowSize": "5 seconds", } glue_context.getSampleStreamingDynamicFrame(YOUR_STREAMING_DF, options, sample_batch_function)

When the sampled DynFrame is empty, it could be caused by a few reasons:

  • The Streaming source is set to "Latest" and no new data has been ingested during the sampling period.

  • The polling time is not enough to process the records it ingested. Data won't show up unless the whole batch has been processed.

Running streaming applications in interactive sessions

In Amazon Glue interactive sessions, you can run a the Amazon Glue streaming application like how you would create a streaming application in the Amazon Glue Console. Since interactive sessions is session-based, encountering exceptions in the runtime does not cause the session to stop. We now have the added benefit of developing your batch function iteratively. For example:

def batch_function(data_frame, batch_id): invalid_method_call() glueContext.forEachBatch(frame=streaming_df, batch_function = batch_function, options = {**})

In the example above, we included an invalid usage of a method and unlike regular Amazon Glue jobs which will exit the entire application, the user's coding context and definitions are fully preserved and the session is still operational. There is no need to bootstrap a new cluster and rerun all the preceding transformation. This allows you to focus on quickly iterating your batch function implementations to obtain desirable outcomes.

It is important to note that Interactive Session evaluates each statement in a blocking manner so that the session will only execute one statement at a time. Since streaming queries are continuous and never ending, sessions with active streaming queries won't be able to handle any follow up statements unless they are interrupted. You can issue the interruption command directly from Jupyter Notebook and our kernel will handle the cancellation for you.

Take the following sequence of statements which are waiting for execution as an example:

Statement 1: val number = df.count() #Spark Action with deterministic result Result: 5 Statement 2: streamingQuery.start().awaitTermination() #Spark Streaming Query that will be executing continously Result: Constantly updated with each microbatch Statement 3: val number2 = df.count() #This will not be executed as previous statement will be running indefinitely