40 lines
2.2 KiB
Markdown
40 lines
2.2 KiB
Markdown
---
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id: high-availability
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title: "High availability"
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---
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Apache ZooKeeper, metadata store, the coordinator, the overlord, and brokers are recommended to set up a high availability environment.
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- For highly-available ZooKeeper, you will need a cluster of 3 or 5 ZooKeeper nodes.
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We recommend either installing ZooKeeper on its own hardware, or running 3 or 5 Master servers (where overlords or coordinators are running)
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and configuring ZooKeeper on them appropriately. See the [ZooKeeper admin guide](https://zookeeper.apache.org/doc/current/zookeeperAdmin) for more details.
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- For highly-available metadata storage, we recommend MySQL or PostgreSQL with replication and failover enabled.
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See [MySQL HA/Scalability Guide](https://dev.mysql.com/doc/mysql-ha-scalability/en/)
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and [PostgreSQL's High Availability, Load Balancing, and Replication](https://www.postgresql.org/docs/current/high-availability.html) for MySQL and PostgreSQL, respectively.
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- For highly-available Apache Druid Coordinators and Overlords, we recommend to run multiple servers.
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If they are all configured to use the same ZooKeeper cluster and metadata storage,
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then they will automatically failover between each other as necessary.
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Only one will be active at a time, but inactive servers will redirect to the currently active server.
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- Druid Brokers can be scaled out and all running servers will be active and queryable.
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We recommend placing them behind a load balancer.
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