Enable connection draining

Connection draining is a process that ensures that existing, in-progress requests are given time to complete when a VM is removed from an instance group or when an endpoint is removed from network endpoint groups (NEGs) that are zonal in scope.

The information on this page applies only to instance groups and the following types of NEGs that are zonal in scope:

To enable connection draining, you set a connection draining timeout on the backend service. The timeout duration must be from 0 to 3600 seconds inclusive.

For the specified duration of the timeout, existing requests to the removed VM or endpoint are given time to complete. The load balancer does not send new TCP connections to the removed VM. After the timeout duration is reached, all remaining TCP connections to the VM are closed.

Connection draining begins whenever you do the following:

It can take up to 60 seconds after your specified timeout duration has passed for the instance to be terminated.

If you enable connection draining on multiple backend services that share the same instance groups or NEGs, the largest timeout value is used. For example, suppose that the same instance group or zonal NEG is a backend for two backend services, where one backend service has a connection draining timeout of 100 seconds, and the other backend service has a connection draining timeout of 200 seconds. Google Cloud uses 200 seconds as the effective connection draining timeout so that existing connections are allowed to exist for 200 seconds before Google Cloud terminates them. If the backend is a managed instance group, operations that delete the instance are delayed by at least 200 seconds.

Following is a list of specifications about connection draining:

To enable connection draining, complete the following steps.

Console

Update a load balancer

  1. Go to the Load balancing page in the Google Cloud console.
    Go to Load balancing
  2. Click Edit for your load balancer or create a new load balancer.
  3. Click Backend configuration.
  4. Click Advanced configurations at the bottom of your backend service.
  5. In the Connection draining timeout field, enter a value from 0 - 3600. A setting of 0 disables connection draining.

Update Traffic Director

  1. Go to the Traffic Director page in the Google Cloud console.
    Go to Traffic Director
  2. Click the Name of your service.
  3. Click Advanced configurations at the bottom of your service.
  4. In the Connection draining timeout field, enter a value from 0 - 3600. A setting of 0 disables connection draining.
  5. Click Save.

gcloud

Enable connection draining on a new or existing backend service by using the --connection-draining-timeout flag. The following examples demonstrate how to change the connection draining timeout:

  • For an existing global or cross-region load balancer:

    gcloud compute backend-services update BACKEND_SERVICE \
        --global \
        --connection-draining-timeout=CONNECTION_TIMEOUT_SECS
    
  • For an existing regional load balancer:

    gcloud compute backend-services update BACKEND_SERVICE \
        --region=REGION \
        --connection-draining-timeout=CONNECTION_TIMEOUT_SECS
    

Replace the placeholders with valid values:

  • BACKEND_SERVICE: The backend service that you're updating.
  • REGION: If applicable, the region of the backend service that you're updating
  • CONNECTION_TIMEOUT_SECS: The number of seconds to wait before existing connections to instances or endpoints are terminated, between 0 - 3600 seconds, inclusive. A setting of 0 disables connection draining. The connection draining timeout applies to all backends of the backend service.

    You can also use the gcloud compute backend-services edit command to update an existing backend service.

API

To enable connection draining in the API when creating or updating an instance or endpoint, make a request to the respective API URI to include the connectionDraining field in your request body. The following examples demonstrate how to set that attribute by editing an existing backend service. For information about other required attributes, see the documentation for each load balancer.

For an existing global or cross-region load balancer:

PATCH https://www.googleapis.com/compute/v1/projects/PROJECT_ID/global/backendServices

For an existing regional load balancer:

PATCH https://www.googleapis.com/compute/v1/projects/PROJECT_ID/region/REGION/backendServices

{
   "name": "BACKEND_SERVICE",
   "connectionDraining": {
     "drainingTimeoutSec": CONNECTION_TIMEOUT_SECS
   }
}

where:

  • PROJECT_ID is the project ID that contains your load balancer or Traffic Director deployment.
  • BACKEND_SERVICE is the backend service used by your load balancer or Traffic Director deployment.
  • CONNECTION_TIMEOUT_SECS is the number of seconds to wait before instances or endpoints are removed from the instance group or NEG, between 0 to 3600 seconds, inclusive. This timeout duration applies to all instance groups or NEGs that are referenced by the backend service.

What's next

For general information on backend services, see Backend services overview.