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Decommissioning
===

## Worker Decommission

Celeborn provides support for decommissioning workers via a REST API, which enables administrators to
efficiently manage cluster resizing and the removal of unhealthy worker nodes without disrupting ongoing jobs.

## Decommission Process

Here's a detailed breakdown of how the decommissioning process works:

- Decommissioning Request: Administrators can send a decommission request through the REST API
to initiate the process for one or more worker nodes.

- Handling New Requests: Once the decommissioning process starts, the affected worker nodes will no longer
accept new shuffle slot requests or new data. This ensures that no new tasks are assigned to
the workers that are set to be decommissioned.

- Existing Data Handling: The worker nodes will continue to handle their existing shuffle partitions
until all the partitions have expired. This mechanism ensures that current jobs running on these nodes
can complete their data shuffle operations without interruption.

- Worker Exit: After all existing shuffle partitions on the worker nodes have expired,
the workers will gracefully exit. This ensures that the node is safely removed from the cluster
without causing data loss or job failures.

This decommissioning process is essential for maintaining cluster health and efficiency,
as it allows for the smooth removal of unhealthy nodes and enables dynamic resizing of the cluster
to meet varying workload demands.

## Decommission Configuration

| Key                                               | Value |
|---------------------------------------------------|-------| 
| celeborn.worker.decommission.forceExitTimeout     | 6h    |
| celeborn.worker.decommission.checkInterval        | 30s   |


## Perform Decommissioning

Administrators perform decommissioning operation in two approaches:

1. Via Celeborn Worker REST API endpoint:
  ```shell
  curl -X POST -H "Content-Type: application/json" -d '{"type":"Decommission"}' http://ip:port/api/v1/workers/exit
  ```
2. Via Celeborn Master(Leader) REST API endpoint:
  ```shell
  curl -X POST -H "Content-Type: application/json" -d '{"eventType":"Decommission","workers":[{"host":"192.168.15.140","rpcPort":"37359","pushPort":"38303","fetchPort":"37569","replicatePort":"37093"},{"host":"192.168.15.141","rpcPort":"37359","pushPort":"38303","fetchPort":"37569","replicatePort":"37093"}]}' http://ip:port/api/v1/workers/events
  curl -X POST -H "Content-Type: application/json" -d '{"eventType":"DecommissionThenIdle","workers":[{"host":"192.168.15.140","rpcPort":"37359","pushPort":"38303","fetchPort":"37569","replicatePort":"37093"},{"host":"192.168.15.141","rpcPort":"37359","pushPort":"38303","fetchPort":"37569","replicatePort":"37093"}]}' http://ip:port/api/v1/workers/events
  ```

Details of decommissioning interface can refer to [REST API](../restapi/#rest-api)

## Decommission Monitoring

Administrators can monitor the status of the workers to ensure they are gracefully exiting
after all tasks are complete.

Administrators can monitor the status of the workers under decommission through worker REST API [ip:port/isDecommissioning](../monitoring/#worker_1)
or worker metrics [IsDecommissioningWorker](../monitoring/#worker).
Also, administrator can monitor count of workers decommissioned through master metrics [DecommissionWorkerCount](../monitoring/#master).

By providing a REST API and metrics for decommissioning workers,
Celeborn ensures that cluster administrators have a robust and flexible tool
to manage cluster resources effectively, enhancing overall system stability and performance.