Serverless App Engine:Idle mode (invitational preview)

When to use Idle mode

Idle mode works best for applications with:

• Sporadic or low traffic — applications that receive requests only during specific time windows (for example, internal tools used during business hours)

• Background workers with idle gaps — batch processing jobs or scheduled tasks that sit idle between runs

• Development and staging environments — non-production applications that stay deployed but rarely receive traffic

If your application receives continuous traffic, instances rarely meet the idle conditions and Idle mode provides little benefit.

How Idle mode works

SAE continuously monitors each instance's CPU usage and inbound network traffic. When all of the following conditions are met simultaneously, the instance enters idle status and is billed at the reduced idle rate:

1. vCPU specification: The instance has 8 or fewer vCPU cores (no memory requirement).

   • For instances with 2 or fewer vCPU cores: actual CPU usage must be below 0.03 cores.

   • For instances with more than 2 and up to 8 vCPU cores: actual CPU usage must be below 1% of the vCPU specification. For example, a 4-core instance must use less than 0.04 cores.

2. Inbound network traffic: Bytes received per instance must be below 20,000 bytes/second. Outbound traffic is not counted.

3. Idle duration cap: Idle billing applies only when idle time accounts for 50% or less of the instance's total runtime. Idle time beyond 50% is billed at the active rate.

If any condition is not met, the instance is billed as active.

Billing

CU conversion coefficients vary by SAE edition, billing status, and server type.

For the full CU pricing details, see Billing.

Enable Idle mode

Before enabling Idle mode, configure graceful start and shutdown for your application. Enabling Idle mode triggers an adjustment to application instances, which may cause brief business interruptions.

1. Go to the SAE application list. At the top of the page, select the target region and namespace, then click the Application ID of your application.

2. On the Basic Information page, click the Auto Scaling tab. In the Idle Mode section, enable Idle mode.

Disable Idle mode

1. Go to the SAE application list. At the top of the page, select the target region and namespace, then click the Application ID of your application.

2. On the Basic Information page, click the Auto Scaling tab. In the Idle Mode section, disable Idle mode.

After disabling Idle mode, all application instances are billed at the active rate.

Verify idle status

After enabling Idle mode, monitor resource usage to confirm that instances are reaching idle status. Switch between the Application and Instance dimensions to view different metrics. Filter by a specific time span or a custom time range.

What prevents instances from reaching idle status

If instances are not entering idle status after enabling Idle mode, check for the following common causes:

• Background health checks or heartbeats — scheduled pings or health probes can keep inbound network traffic above 20,000 bytes/second.

• vCPU specification exceeds 8 cores — instances with more than 8 vCPU cores are never eligible for idle billing, regardless of actual usage.

• Continuous background CPU activity — background processes that keep CPU usage above the idle threshold.

• Persistent inbound connections — inbound connections that receive frequent data count toward the 20,000 bytes/second inbound limit.

• Idle duration cap exceeded — if an instance has already been idle for more than 50% of its total runtime, further idle time in that period is billed as active.

Use the Instance dimension in the resource usage view to check CPU usage (cores) and bytes received (B/s) for individual instances to identify which condition is blocking idle status.