When setting up an auto-scaling policy for a SageMaker endpoint, the Invocation Safety Factor is a crucial parameter for striking a balance between cost-effectiveness and responsiveness to traffic surges. Here's how it works:

• Purpose: The safety factor acts as a buffer, preventing the auto-scaling policy from rapidly scaling up your endpoint's instance count based on a fleeting spike in requests. It safeguards against unnecessarily scaling up instances when short-term bursts in traffic occur.
• How It Works:
  1. You determine a maximum requests per second (max RPS) your endpoint can reliably handle with the current instance configuration.
  2. The Invocation Safety Factor is a number (usually between 0 and 1) you multiply by the max RPS to get a threshold.
  3. Your auto-scaling policy is configured to only scale up if the incoming request rate consistently exceeds this threshold.

Example:

• You determine your endpoint can handle a maximum of 50 RPS.
• You set an Invocation Safety Factor of 0.8.
• The scaling threshold is calculated as 50 RPS * 0.8 = 40 RPS.
• Your endpoint will only add instances if the incoming traffic consistently stays above 40 RPS.

Benefits of the Invocation Safety Factor

• Cost Control: Prevents your endpoint from scaling up too quickly due to short-term fluctuations in traffic, preventing unnecessary costs.
• Stability: Provides a degree of protection against over-provisioning, improving service stability.

Choosing a Safety Factor

The optimal safety factor depends on your use case and tolerance for latency:

• High Latency Tolerance: A higher safety factor (closer to 1) provides better cost control but might add latency during traffic bursts.
• Low Latency Tolerance: A lower safety factor (closer to 0) makes your endpoint more responsive at the potential cost of slightly higher costs due to more frequent scaling.

Important Considerations:

• The Invocation Safety Factor works alongside other auto-scaling parameters in Amazon SageMaker (e.g., target utilization).
• Carefully monitor your endpoint's metrics to find the right balance for your application.