Pipeline Components and Applications

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  6. Loading transformed data
  7. Monitoring

Monitoring

The loader app has several types of monitoring built in to help the pipeline operator: folder monitoring, warehouse health checks, StatsD metrics, Sentry alerts, and Snowplow tracking.

For all monitoring configuration options, see the configuration reference.

Webhook alerts

The loader can send POST requests via HTTP webhook to a configurable URL whenever there is an issue which needs investigation by the pipeline operator. The webhook payload conforms to the alert schema on Iglu Central.

You can configure where the webhook is sent by setting the monitoring.webhook section in the config.hocon file.

The webhook monitoring can be used for folder monitoring and warehouse health checks.

Folder monitoring

A webhook alert is sent whenever the loader identifies inconsistencies between the transformed output in S3 and the data in the warehouse. The algorithm is as follows:

  • Check if all folders on S3 have a shredding_complete.json file (the legacy name is kept for backwards compatibility, but this applies to wide row format data as well). A missing file suggests the transformer failed to complete writing the transformed data, and so manual intervention is required to remove the folder from S3 and rerun.
  • Check if all folders on S3 created within a specific time range are listed in the warehouse manifest table. This table is maintained by the loader and contains information about loads. If a folder is missing from the manifest table, it suggests the loader has previously tried and failed to load it. Manual intervention is required to resend the shredding_complete.json message via SQS / SNS to trigger reloading of the folder.

Folder monitoring is configured by setting the monitoring.folders section in the config.hocon file.

Warehouse health check

The loader can send an alert if the warehouse does not respond to a periodic SELECT 1 statement. For each failed health check, a POST request is sent via the webhook.

The health check is configured by setting the monitoring.healthCheck section in the config.hocon file.

StatsD and stdout

StatsD is a daemon that aggregates and summarizes application metrics. It receives metrics sent by the application over UDP, and then periodically flushes the aggregated metrics to a pluggable storage backend.

The loader can emit metrics to a StatsD daemon describing every batch it processes. Here is a string representation of the metrics it sends:

snowplow.rdbloader.count_good:42|c|#tag1:value1 snowplow.rdbloader.latency_collector_to_load_min:123.4|g|#tag1:value1 snowplow.rdbloader.latency_collector_to_load_max:234.5|g|#tag1:value1 snowplow.rdbloader.latency_transformer_start_to_load:66.6|g|#tag1:value1 snowplow.rdbloader.latency_transformer_end_to_load:44.4|g|#tag1:value1
Code language: plaintext (plaintext)

These are the meanings of the individual metrics:

  • count_good: the total number of good events in the batch that was loaded
  • latency_collector_to_load_min: for the most recent event in the batch, this is the time difference between reaching the collector and getting loaded to the warehouse
  • latency_collector_to_load_min: for the oldest event in the batch, this is the time difference between reaching the collector and getting loaded to the warehouse
  • latency_transformer_start_to_load: time difference between the transformer starting on this batch and the loader completing loading to the warehouse
  • latency_transformer_end_to_load: time difference between the transformer completing this batch and the loader completing loading it into the warehouse.

StatsD monitoring is configured by setting the monitoring.metrics.statsd section in the config.hocon file.

You can expose these metrics in stdout for easier debugging by setting the monitoring.metrics.stdout section in the config.hocon file.

Sentry

Sentry is a popular error monitoring service, which helps developers diagnose and fix problems in an application. The loader and transformer can both send an error report to sentry whenever something unexpected happens. The reasons for the error can then be explored in the Sentry server’s UI.

Common reasons might be lost connection to the database, or an HTTP error fetching a schema from an Iglu server.

Sentry monitoring is configured by setting the monitoring.sentry.dsn section in the config.hocon file.

Snowplow tracking

The loader can emit a Snowplow event to a collector when the application crashes with an unexpected error. The event conforms to the load_failed schema on Iglu Central.

Snowplow tracking is configured by setting the monitoring.snowplow section in the config.hocon file.