如何缩小CrateDB集群的规模？

Question

为了进行测试，我想将我的3节点集群缩小到2节点，然后对我的5节点集群执行同样的操作。

然而，在遵循缩小集群的最佳实践之后：

1. 备份所有桌子
2. 对于所有表:如果它之前小于2，则为alter table xyz set (number_of_replicas=2)
3. SET GLOBAL PERSISTENT discovery.zen.minimum_master_nodes = <half of the cluster + 1>; 3 a.如果数据检查应该始终是绿色的，则将min_availability设置为“full”：https://crate.io/docs/reference/configuration.html#graceful-stop
4. 在一个节点上启动优美的停止
5. 等待数据检查变成绿色
6. 从3开始重复。
7. 完成后，将节点配置保持在crate.yml：gateway.recover_after_nodes: n discovery.zen.minimum_master_nodes:[![enter image description here][1]][1] (n/2) +1 gateway.expected_nodes: n中。

我的集群再也没有返回到“绿色”，我也有一个关键节点检查失败。

这里出了什么问题？

crate.yml：

  ... 
  ################################## Discovery ##################################

  # Discovery infrastructure ensures nodes can be found within a cluster
  # and master node is elected. Multicast discovery is the default.

  # Set to ensure a node sees M other master eligible nodes to be considered
  # operational within the cluster. Its recommended to set it to a higher value
  # than 1 when running more than 2 nodes in the cluster.
  #
  # We highly recommend to set the minimum master nodes as follows:
  #   minimum_master_nodes: (N / 2) + 1 where N is the cluster size
  # That will ensure a full recovery of the cluster state.
  #
  discovery.zen.minimum_master_nodes: 2

  # Set the time to wait for ping responses from other nodes when discovering.
  # Set this option to a higher value on a slow or congested network
  # to minimize discovery failures:
  #
  # discovery.zen.ping.timeout: 3s
  #

  # Time a node is waiting for responses from other nodes to a published
  # cluster state.
  #
  # discovery.zen.publish_timeout: 30s

  # Unicast discovery allows to explicitly control which nodes will be used
  # to discover the cluster. It can be used when multicast is not present,
  # or to restrict the cluster communication-wise.
  # For example, Amazon Web Services doesn't support multicast discovery.
  # Therefore, you need to specify the instances you want to connect to a
  # cluster as described in the following steps:
  #
  # 1. Disable multicast discovery (enabled by default):
  #
  discovery.zen.ping.multicast.enabled: false
  #
  # 2. Configure an initial list of master nodes in the cluster
  #    to perform discovery when new nodes (master or data) are started:
  #
  # If you want to debug the discovery process, you can set a logger in
  # 'config/logging.yml' to help you doing so.
  #
  ################################### Gateway ###################################

  # The gateway persists cluster meta data on disk every time the meta data
  # changes. This data is stored persistently across full cluster restarts
  # and recovered after nodes are started again.

  # Defines the number of nodes that need to be started before any cluster
  # state recovery will start.
  #
  gateway.recover_after_nodes: 3

  # Defines the time to wait before starting the recovery once the number
  # of nodes defined in gateway.recover_after_nodes are started.
  #
  #gateway.recover_after_time: 5m

  # Defines how many nodes should be waited for until the cluster state is
  # recovered immediately. The value should be equal to the number of nodes
  # in the cluster.
  #
  gateway.expected_nodes: 3

Answer 1

所以有两件事很重要：

• 副本的数量实质上是典型设置中可以松散的节点数(推荐使用2个副本，这样就可以缩小和松散进程中的节点，但仍然可以)
• 建议在集群>2个节点时使用此过程;)

CrateDB将以没有副本和主节点共享的方式在集群中自动分发碎片。如果这是不可能的(如果您有2个节点和1个主节点以及2个副本，则数据检查将永远不会返回到“green”。因此，在您的示例中，将副本的数量设置为1，以便将集群恢复为绿色(alter table mytable set (number_of_replicas = 1))。

关键节点检查是由于集群还没有收到更新的crate.yml :您的文件中还有一个3节点集群的配置，因此产生了消息。由于CrateDB只在启动时加载expected_nodes (它是不是运行时设置)，因此需要重新启动整个集群才能完成缩小。它可以通过滚动重新启动来完成，但是一定要正确地设置SET GLOBAL PERSISTENT discovery.zen.minimum_master_nodes = <half of the cluster + 1>;，否则协商一致将无法工作.

此外，还建议一个一个地缩小规模，以避免重新平衡和意外地丢失数据，从而使集群超载。