94 lines
6.2 KiB
Markdown
94 lines
6.2 KiB
Markdown
# Zookeeper Single Pair Failback Example
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This example demonstrates two servers coupled as a primary-backup pair for high availability (HA) using
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pluggable quorum vote replication Reference Implementation based on [Apache Curator](https://curator.apache.org/) to use
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[Apache Zookeeper](https://zookeeper.apache.org/) as external quorum service.
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The example shows a client connection failing over from live to backup when the live broker is crashed and
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then back to the original live when it is restarted (i.e. "failback").
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To run the example, simply type **mvn verify** from this directory after running a Zookeeper node at `localhost:2181`.
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If no Zookeeper node is configured, can use the commands below (see [Official Zookeeper Docker Image Site](https://hub.docker.com/_/zookeeper)
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for more details on how configure it).
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Run Zookeeper `3.6.3` with:
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```
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$ docker run --name artemis-zk --network host --restart always -d zookeeper:3.6.3
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```
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By default, the official docker image exposes `2181 2888 3888 8080` as client, follower, election and AdminServer ports.
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Verify Zookeeper server is correctly started by running:
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```
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$ docker logs --follow artemis-zk
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```
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It should print the Zookeeper welcome ASCII logs:
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```
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ZooKeeper JMX enabled by default
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Using config: /conf/zoo.cfg
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2021-08-05 14:29:29,431 [myid:] - INFO [main:QuorumPeerConfig@174] - Reading configuration from: /conf/zoo.cfg
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2021-08-05 14:29:29,434 [myid:] - INFO [main:QuorumPeerConfig@451] - clientPort is not set
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2021-08-05 14:29:29,434 [myid:] - INFO [main:QuorumPeerConfig@464] - secureClientPort is not set
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2021-08-05 14:29:29,434 [myid:] - INFO [main:QuorumPeerConfig@480] - observerMasterPort is not set
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2021-08-05 14:29:29,435 [myid:] - INFO [main:QuorumPeerConfig@497] - metricsProvider.className is org.apache.zookeeper.metrics.impl.DefaultMetricsProvider
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2021-08-05 14:29:29,438 [myid:] - ERROR [main:QuorumPeerConfig@722] - Invalid configuration, only one server specified (ignoring)
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2021-08-05 14:29:29,441 [myid:1] - INFO [main:DatadirCleanupManager@78] - autopurge.snapRetainCount set to 3
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2021-08-05 14:29:29,441 [myid:1] - INFO [main:DatadirCleanupManager@79] - autopurge.purgeInterval set to 0
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2021-08-05 14:29:29,441 [myid:1] - INFO [main:DatadirCleanupManager@101] - Purge task is not scheduled.
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2021-08-05 14:29:29,441 [myid:1] - WARN [main:QuorumPeerMain@138] - Either no config or no quorum defined in config, running in standalone mode
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2021-08-05 14:29:29,444 [myid:1] - INFO [main:ManagedUtil@44] - Log4j 1.2 jmx support found and enabled.
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2021-08-05 14:29:29,449 [myid:1] - INFO [main:QuorumPeerConfig@174] - Reading configuration from: /conf/zoo.cfg
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2021-08-05 14:29:29,449 [myid:1] - INFO [main:QuorumPeerConfig@451] - clientPort is not set
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2021-08-05 14:29:29,449 [myid:1] - INFO [main:QuorumPeerConfig@464] - secureClientPort is not set
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2021-08-05 14:29:29,449 [myid:1] - INFO [main:QuorumPeerConfig@480] - observerMasterPort is not set
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2021-08-05 14:29:29,450 [myid:1] - INFO [main:QuorumPeerConfig@497] - metricsProvider.className is org.apache.zookeeper.metrics.impl.DefaultMetricsProvider
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2021-08-05 14:29:29,450 [myid:1] - ERROR [main:QuorumPeerConfig@722] - Invalid configuration, only one server specified (ignoring)
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2021-08-05 14:29:29,451 [myid:1] - INFO [main:ZooKeeperServerMain@122] - Starting server
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2021-08-05 14:29:29,459 [myid:1] - INFO [main:ServerMetrics@62] - ServerMetrics initialized with provider org.apache.zookeeper.metrics.impl.DefaultMetricsProvider@525f1e4e
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2021-08-05 14:29:29,461 [myid:1] - INFO [main:FileTxnSnapLog@124] - zookeeper.snapshot.trust.empty : false
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2021-08-05 14:29:29,467 [myid:1] - INFO [main:ZookeeperBanner@42] -
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2021-08-05 14:29:29,467 [myid:1] - INFO [main:ZookeeperBanner@42] - ______ _
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2021-08-05 14:29:29,467 [myid:1] - INFO [main:ZookeeperBanner@42] - |___ / | |
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2021-08-05 14:29:29,467 [myid:1] - INFO [main:ZookeeperBanner@42] - / / ___ ___ | | __ ___ ___ _ __ ___ _ __
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2021-08-05 14:29:29,468 [myid:1] - INFO [main:ZookeeperBanner@42] - / / / _ \ / _ \ | |/ / / _ \ / _ \ | '_ \ / _ \ | '__|
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2021-08-05 14:29:29,468 [myid:1] - INFO [main:ZookeeperBanner@42] - / /__ | (_) | | (_) | | < | __/ | __/ | |_) | | __/ | |
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2021-08-05 14:29:29,468 [myid:1] - INFO [main:ZookeeperBanner@42] - /_____| \___/ \___/ |_|\_\ \___| \___| | .__/ \___| |_|
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2021-08-05 14:29:29,468 [myid:1] - INFO [main:ZookeeperBanner@42] - | |
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2021-08-05 14:29:29,468 [myid:1] - INFO [main:ZookeeperBanner@42] - |_|
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2021-08-05 14:29:29,468 [myid:1] - INFO [main:ZookeeperBanner@42] -
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```
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Alternatively, can run
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```
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$ docker run -it --rm --network host zookeeper:3.6.3 zkCli.sh -server localhost:2181
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```
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Zookeeper server can be reached using localhost:2181 if it output something like:
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```
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2021-08-05 14:56:03,739 [myid:localhost:2181] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1448] - Session establishment complete on server localhost/0:0:0:0:0:0:0:1:2181, session id = 0x100078b8cfc0002, negotiated timeout = 30000
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```
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Type
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```
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[zk: localhost:2181(CONNECTED) 0] quit
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```
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to quit the client instance.
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The 2 brokers of this example are already configured to connect to a single Zookeeper node at the mentioned address, thanks to the XML configuration of their `manager`:
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```xml
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<manager>
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<properties>
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<property key="connect-string" value="localhost:2181"/>
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<property key="namespace" value="examples"/>
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<property key="session-ms" value="18000"/>
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</properties>
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</manager>
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```
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**NOTE** the `namespace` parameter is used to separate the pair information from others if the Zookeeper node is shared with other applications.
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**WARNING** As already recommended on the [High Availability section](https://activemq.apache.org/components/artemis/documentation/latest/ha.html), a production environment needs >= 3 nodes to protect against network partitions.
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This example can be run with
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```
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$ mvn verify
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```
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For more information on ActiveMQ Artemis failover and HA, and clustering in general, please see the clustering section of the user manual. |