fix: prevent orphaned DynamoDB entries when Kinesis shards close during pod termination

[matus-tomlein]

Summary

Fixes #643

This PR addresses a race condition where DynamoDB lease table entries for closed Kinesis shards are not cleaned up when Bento pods are terminated during Kubernetes scaling events.

Changes

1. Fix Shutdown Logic (input_kinesis.go:486-507)

Modified the awsKinesisConsumerClosing case to detect finished shards:

case awsKinesisConsumerClosing:
    // If the iterator is empty, the shard is finished and should be deleted
    // rather than checkpointed. This prevents orphaned DynamoDB entries when
    // pods are terminated after Kinesis closes shards but before consumption completes.
    //
    // Note: There's an edge case where if a shard naturally finishes (state becomes
    // awsKinesisConsumerFinished) but the pod is terminated before this defer runs,
    // the state will be changed to awsKinesisConsumerClosing. This means Delete could
    // be called from both code paths, but this is safe because Delete is idempotent.
    if iter == "" {
        // Use context.Background() to ensure the delete completes even during shutdown
        k.checkpointer.Delete(context.Background(), ...)
    } else {
        k.checkpointer.Checkpoint(..., final=true)
    }

What this fixes: When a pod is terminated and the shard iterator is empty (shard closed and fully consumed), the DynamoDB entry is now deleted instead of leaving an orphaned checkpoint.

2. Add Periodic Cleanup (input_kinesis.go:700-746)

Added proactive cleanup in the rebalancing loop (runs every 30s by default) with two phases:

Phase 1: Clean up entries with expired leases

for clientID, claims := range clientClaims {
    for _, claim := range claims {
        if finishedShardIDs[claim.ShardID] {
            isExpired := time.Since(claim.LeaseTimeout) > k.leasePeriod*2
            if isExpired {
                k.checkpointer.Delete(...)
            } else {
                k.log.Debugf("Skipping cleanup of finished shard '%v' from client '%v' (lease still active)", ...)
            }
        }
    }
}

Phase 2: Clean up orphaned entries (no ClientID)

orphanedShards, err := k.checkpointer.OrphanedShards(k.ctx, info.id)
for _, shardID := range orphanedShards {
    if finishedShardIDs[shardID] {
        k.checkpointer.Delete(...)
    }
}

3. New OrphanedShards Method (input_kinesis_checkpointer.go:183-208)

Added method to query DynamoDB entries without ClientID:

func (k *awsKinesisCheckpointer) OrphanedShards(ctx context.Context, streamID string) ([]string, error) {
    scanRes, err := k.svc.Scan(ctx, &dynamodb.ScanInput{
        TableName:        aws.String(k.conf.Table),
        FilterExpression: aws.String("StreamID = :stream_id AND attribute_not_exists(ClientID)"),
        ...
    })
    ...
}

Why needed: The existing AllClaims() function skips entries without ClientID, so a separate query is required to find truly orphaned entries created by Checkpoint(final=true).

Safety

• k.checkpointer.Delete() is idempotent (safe to call multiple times)
• DynamoDB DeleteItem succeeds even if the item doesn't exist
• Lease expiry check prevents interfering with active consumers
• Detailed debug logging for all cleanup scenarios
• No data corruption or duplicate processing risk

Testing

• Existing tests pass
• Code compiles successfully
• Changes are backward compatible

Impact

• Eliminates false positive latency alerts
• Removes need for manual DynamoDB cleanup
• Resolves recurring production incidents
• Enhanced observability with detailed logging

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com

[Copilot]

Pull request overview

This pull request fixes a race condition where DynamoDB lease table entries for closed Kinesis shards are not cleaned up when Bento pods are terminated during Kubernetes scaling events, leading to orphaned entries and false positive latency alerts.

• Adds conditional cleanup logic during pod shutdown to delete checkpoints for finished shards instead of saving them
• Implements periodic background cleanup that removes DynamoDB entries for shards that have been closed by Kinesis

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Pull request overview

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