Why ALB Targets Skip Slow Start Mode

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 ALB configuration uses the round robin routing algorithm for traffic.
The target group did not contain at least one healthy target configured in slow start mode. Source Reference Answer
The target group must contain EC2 instances that are all the same instance type.
The ALB configuration uses the 5-tuple criteria for traffic.

Community Votes

100%

100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Community Insight

Tests the specific condition where simultaneous registration of all initial targets prevents the slow start mechanism from activating.

AWS ALB slow start mode prevents traffic overload on new targets by gradually increasing connections. Community consensus confirms that registering multiple targets simultaneously into an empty group bypasses this feature.

Candidates often assume slow start is always enabled once configured, missing the critical requirement for existing healthy targets.

Community Discussion (3 comments)

billgoldberg14 👍 5 Selected: B

Looks like the answer is B according to this link: https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html#slow-start-mode " When you enable slow start for an empty target group and then register targets using a single registration operation, these targets do not enter slow start mode. Newly registered targets enter slow start mode only when there is at least one healthy target that is not in slow start mode."

woorkim 👍 3 Selected: B

When you enable slow start for an empty target group and then register targets using a single registration operation, these targets do not enter slow start mode. Newly registered targets enter slow start mode only when there is at least one healthy target that is not in slow start mode.

cas_tori 👍 2 Selected: B

this is B

Comments & Corrections

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Expert Analysis

Why the Answer Is Correct

Slow start mode requires at least one healthy target not in slow start to exist before new targets are added. When you register targets using a single operation (batch) into an empty target group, AWS treats them as the initial set. Consequently, they do not enter slow start mode because there is no existing baseline target to trigger the gradual ramp-up logic.

Why the Other Options Are Wrong

Options A and D refer to routing algorithms (Round Robin or 5-tuple), which determine how traffic is distributed among active targets but do not control the initialization behavior of new targets. Option C is incorrect because ALB target groups support mixed instance types; homogeneity is not a requirement for slow start functionality.

Community Comment Notes

Comments [1] and [2] correctly cite the official AWS documentation stating that newly registered targets only enter slow start when there is already a healthy target present. This highlights the importance of reading the fine print regarding 'single registration operations' vs. incremental additions.

Official Reference

https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html#slow-start-mode

Exam Strategy

Always check if the scenario involves batch registration versus incremental scaling. If all targets are added at once to an empty group, features like slow start or connection draining may behave differently than expected.

Related Analysis

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