Startup Rules

Definitions of Hosts

Healthy Hosts

Definition: Hosts that are operating normally and have passed health checks.

Characteristics:

• Host status is “Normal”.
• Have passed the health check of ULB.

Initializing Hosts

Definition: Hosts that are starting up, being configured, or newly created but not fully ready yet.

Characteristics:

• Host status is “Initializing”.
• Host status is “Normal” but hasn’t passed the health check, and the creation time is within the predefined cooling period.

Unhealthy Hosts

Definition: Hosts that have completed initialization but failed to pass the health check.

Characteristics:

• Host status is “Normal”.
• Failed the ULB health check, and the creation time exceeds the predefined cooling period.

Host Quantity Range Rules

• Target 1 (Scaling Up Logic): Healthy Hosts + Initializing Hosts ≥ Minimum Quantity
• Target 2 (Scaling Down Logic): Healthy Hosts + Initializing Hosts + Unhealthy Hosts ≤ Maximum Quantity
• When scaling up (triggered by Target 1), check if the post-scaling host count meets Target 2; cancel scaling up if not.

CPU Rules

• Processing is only performed when CPU metric calculations indicate a need to change the number of hosts.
• Ensure the post-change host count does not violate the minimum/maximum limits.
• Scaling quantity calculation formula: delta = (AvgGroupCPU * ActiveCount / cpuExpected) - ActiveCount.

• When scaling up (delta > 0), exclude initializing hosts: delta = max(delta - InitCount, 0)
• Scaling quantity (delta ≠ 0) must not exceed the host quantity range.

Health Rules

1. Record the number of unhealthy hosts every two minutes.
2. Hosts recorded as unhealthy for three consecutive times will be removed.

Notes:

1. Hosts with removal protection enabled will not be deleted by the rules.
2. During downsizing, earlier created hosts and those automatically created by the scaling group will be removed first.