Project: Druid (App Definition and Development / Database)
File: rolling-updates.md

id: rolling-updates title: "Rolling updates" <!-- ~ Licensed to the Apache Software Foundation (ASF) under one ~ or more contributor license agreements. See the NOTICE file ~ distributed with this work for additional information ~ regarding copyright ownership. The ASF licenses this file ~ to you under the Apache License, Version 2.0 (the ~ "License"); you may not use this file except in compliance ~ with the License. You may obtain a copy of the License at ~ ~ http://www.apache.org/licenses/LICENSE-2.0 ~ ~ Unless required by applicable law or agreed to in writing, ~ software distributed under the License is distributed on an ~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY ~ KIND, either express or implied. See the License for the ~ specific language governing permissions and limitations ~ under the License. --> For rolling Apache Druid cluster updates with no downtime, we recommend updating Druid processes in the following order: Historical Middle Manager and Indexer (if any) Broker Router Overlord (Note that you can upgrade the Overlord before any MiddleManager processes if you use .) Coordinator ( or merged Coordinator+Overlord ) If you need to do a rolling downgrade, reverse the order and start with the Coordinator processes. For information about the latest release, see . Historical processes can be updated one at a time. Each Historical process has a startup time to memory map all the segments it was serving before the update. The startup time typically takes a few seconds to a few minutes, depending on the hardware of the host. As long as each Historical process is updated with a sufficient delay (greater than the time required to start a single process), you can rolling update the entire Historical cluster. Overlord processes can be updated one at a time in a rolling fashion. Middle Managers or Indexer nodes run both batch and real-time indexing

Generally you want to update Middle Managers in such a way that real-time indexing tasks do not fail. There are three strategies for doing that. Middle Managers can be updated one at a time in a rolling fashion when you set `druid.indexer.task.restoreTasksOnRestart=true`. In this case, indexing tasks that support restoring will restore their state on Middle Manager restart, and will not fail. Currently, only realtime tasks support restoring, so non-realtime indexing tasks will fail and will need to be resubmitted. Middle Managers can be gracefully terminated using the "disable" API. This works for all task types, even tasks that are not restorable. To prepare a Middle Manager for update, send a POST request to `<MiddleManager_IP:PORT>/druid/worker/v1/disable`. The Overlord will now no longer send tasks to this Middle Manager. Tasks that have already started will run to completion. Current state can be checked using `<MiddleManager_IP:PORT>/druid/worker/v1/enabled` . To view all existing tasks, send a GET request to `<MiddleManager_IP:PORT>/druid/worker/v1/tasks`. When this list is empty, you can safely update the Middle Manager. After the Middle Manager starts back up, it is automatically enabled again. You can also manually enable Middle Managers by POSTing to `<MiddleManager_IP:PORT>/druid/worker/v1/enable`. If autoscaling is enabled on your Overlord, then Overlord processes can launch new Middle Manager processes en masse and then gracefully terminate old ones as their tasks finish. This process is configured by setting `druid.indexer.runner.minWorkerVersion=#{VERSION}`. Each time you update your Overlord process, the `VERSION` value should be increased, which will trigger a mass launch of new Middle Managers. The config `druid.indexer.autoscale.workerVersion=#{VERSION}` also needs to be set. Standalone real-time processes can be updated one at a time in a rolling fashion. Broker processes can be updated one at a time in a rolling fashion. There needs to be some delay between updating each process as Brokers must load the entire state of the cluster before they return valid results. Coordinator processes can be updated one at a time in a rolling fashion.