ZooKeeper

cosid-zookeeper stores segment counters and machine id leases in ZooKeeper, through Apache Curator:

• ZookeeperIdSegmentDistributor: segment counters, as Curator distributed atomic longs.
• ZookeeperMachineLeaseStore: machine id leases, claimed and released with versioned transactions.

ZooKeeper has no server clock that clients can read, so lease times come from the host clocks. Keep the hosts' clocks in sync (NTP): an instance whose clock runs ahead can see another instance's lease as expired before it is.

The starter creates the Curator client when a type selects ZooKeeper, or when cosid.zookeeper.enabled=true is set explicitly. Left unset, it is created only when selected; false turns it off.

Installation

Gradle (Kotlin)

dependencies {
    implementation(platform("me.ahoo.cosid:cosid-bom:$cosidVersion"))
    implementation("me.ahoo.cosid:cosid-spring-boot-starter")
    implementation("me.ahoo.cosid:cosid-zookeeper")
}

Maven

<dependencies>
    <dependency>
        <groupId>me.ahoo.cosid</groupId>
        <artifactId>cosid-spring-boot-starter</artifactId>
    </dependency>
    <dependency>
        <groupId>me.ahoo.cosid</groupId>
        <artifactId>cosid-zookeeper</artifactId>
    </dependency>
</dependencies>

cosid-zookeeper brings curator-recipes.

Configuration

cosid:
  namespace: ${spring.application.name}
  zookeeper:
    connect-string: localhost:2181
  machine:
    enabled: true # for Snowflake IDs and CosIdGenerator
    distributor:
      type: zookeeper
  segment:
    enabled: true # for segment IDs
    distributor:
      type: zookeeper

Property	Default	Description
cosid.zookeeper.enabled	not set	true creates the Curator client even when no type selects ZooKeeper; false turns it off; unset, it is created only when selected
cosid.zookeeper.connect-string	localhost:2181	ZooKeeper servers
cosid.zookeeper.session-timeout	60s	Session timeout
cosid.zookeeper.connection-timeout	15s	Connection timeout
cosid.zookeeper.block-until-connected-wait	10s	How long startup waits for the connection
cosid.zookeeper.retry.base-sleep-time-ms	100	ExponentialBackoffRetry: initial wait between retries, in milliseconds
cosid.zookeeper.retry.max-retries	5	Maximum retries
cosid.zookeeper.retry.max-sleep-ms	500	Maximum wait between retries, in milliseconds
cosid.segment.distributor.zookeeper.timeout	5s	Each segment nextMaxId; 0 disables it
cosid.machine.distributor.zookeeper.timeout	5s	Lease renewal and release (Curator has no per-operation timeout); must be positive

An application can define its own CuratorFramework bean instead. See CosId-Example-Zookeeper for a runnable application.