A company is building a new workload on AWS that uses an Application Load Balancer (ALB) The company has configured a new ALB target group that uses slow start mode. A team begins registering Amazon EC2 Instances as targets in the new target group. During testing, the team observes that the targets did not enter slow start mode. What caused the targets to not enter slow start mode?

The slow start feature is designed to gradually introduce a new target to a target group to allow it to "warm up" without being overwhelmed. This mechanism relies on other healthy targets being available to handle the full traffic load while the new target is ramping up. According to AWS documentation, if a target group has no other healthy targets (e.g., it's empty or all existing targets are unhealthy), a newly registered target will bypass slow start mode to begin serving traffic immediately.

A. The routing algorithm (round robin or least outstanding requests) determines how traffic is distributed among healthy targets but does not influence the initiation of slow start mode.
C. The instance type of targets within a target group has no effect on the behavior of slow start mode. Target groups support heterogeneous instance types.
D. The 5-tuple criteria is used for flow hashing, primarily associated with Network Load Balancers, and is not relevant to how an Application Load Balancer implements slow start.

1. Elastic Load Balancing Documentation. (n.d.). Slow start mode. AWS. Retrieved from https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html#slow-start-mode (The documentation states, "If you register a single target with a target group that has slow start enabled, the target does not enter slow start mode.").

2. Elastic Load Balancing Documentation. (n.d.). Troubleshoot your Application Load Balancers. AWS. Retrieved from https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-troubleshooting.html (Under "A registered target is not in service," it reiterates that slow start is bypassed if there are no other healthy targets to serve traffic).