The termination sequence ensures a controlled and graceful process for removing workload replicas from the load balancer pool and handling container termination. The use of a preStop hook, either default or custom, can be leveraged to manage termination and connections as per the workload’s requirements. Termination occurs most often when a workload is being scaled down or when an old version of the workload is taken offline after a successful update to a new version. In rare cases, maintenance activities can cause workload replicas to be rescheduled and terminated. The steps below are performed for each replica of the workload.
  1. Load Balancer Update: At the initiation of workload termination, load balancers are sent a command to remove the workload replica from the pool.
  2. Workload Sidecar and Containers Termination: The workload sidecar (managed by Control Plane) and all other workload containers are sent a command to begin their termination process. This happens at nearly the same time as step 1.
  3. Load Balancer Routing: Once the load balancer is updated, any new incoming requests will be routed to the remaining healthy workload replicas for the workload.
  4. Sidecar Monitoring: The sidecar managed by Control Plane continues to monitor network activity. It will remain running until no more active requests exist and connections terminate, for a maximum duration of up to 90 seconds.
  5. Default PreStop Hook: If no customer-defined preStop hook is provided, a default preStop hook is applied to all workload containers. This default hook consists of the “sleep” command with a duration of 45 seconds. Once the sleep command completes, the container is sent a SIGTERM signal and allowed to gracefully shutdown for an additional 45 seconds before receiving a SIGKILL signal.
If the “sleep” executable is not available in the customer’s workload container, the container will be sent a graceful termination signal immediately. Requests might still reach it before the load balancer is fully updated.
  1. Custom PreStop Hook (Optional): It is recommended to add a custom preStop hook only if specific custom logic is required, such as gracefully terminating connections that would not otherwise terminate. If a custom preStop hook is implemented, ensure it includes a delay or a check for existing requests before exiting. Once the preStop hook completes the container will receive a signal to terminate gracefully (SIGTERM) and will have up to 90 seconds from the start of the shutdown process to complete.
Please note that implementing a custom preStop hook is only advisable when additional logic is necessary for your specific workload termination needs.