Awaitility VS Apache ZooKeeper

I’ve coded in Java since the first beta, even back then threads were at the top of my list of favorite features. Java was the first language to introduce thread support in the language itself, it was a controversial decision back then. In the past decade, every language raced to include async/await and even Java had some third-party support for that… But Java zigged instead of zagging and introduced the far superior virtual threads (project Loom). This post isn’t about that.

I hope everybody knows https://github.com/awaitility/awaitility by now.

And finally the tests, using Awaitility as we are testing asynchronous stuff:

awaitability: A tool to express expectations for asynchronous system in an easy and concise manner.

Awaitility with version 4.1.0 comes with fail fast feature (2m read) 🎉 https://github.com/awaitility/awaitility/wiki/Usage#fail-fast-conditions

Given our new functionality to update the membership list, we can create a new test case where two nodes join the cluster and expect that to be reflected in the local state of each node eventually. Thanks to the Awaitility DSL we can conveniently wait for the eventual update to happen.

Nota: para los que no la conozcáis, await es un operador de awaitility, muy útil para validación de resultados en procesos asíncronos.

Apache ZooKeeper — a distributed coordination, synchronization, and configuration service (written in Java);

To use Kafka, we also need to deploy a service that keeps configuration informations such as Zookeeper.

Failure Detection and Recovery It’s not enough to have backup systems. It’s also crucial to detect failures quickly. Modern systems employ monitoring tools and rely on distributed coordination systems such as Zookeeper or etcd to identify faults in real-time: once detected, recovery mechanisms are triggered to restore the service.

zookeeper: is (was?) used for secrets management. it was also used as a basic health check, but has been since been replaced.

You can install Kafka from https://kafka.apache.org/quickstart. Because Druid and Kafka both use Apache Zookeeper, I opted to use the Zookeeper deployment that comes with Druid, so didn’t start it with Kafka. Once running, I created two topics for me to post the data into, and for Druid to ingest from:

Please note that we use Zookeeper as the Governance Center.

Next, review deployment complexity such as DB-less versus database-backed deployments. For example, Kong does require running Cassandra or Postgres. Apigee requires Cassandra, Zookeeper, and Postgres to run, while other solutions like Express Gateway and Tyk only require Redis. Apache APISIX uses etcd as its data store, it stores and manages routing-related and plugin-related configurations in etcd in the Data Plane.

ZooKeeper, a system for coordinating distributed nodes, similar to Google's Chubby

[Unit] Description=Apache Zookeeper server Documentation=http://zookeeper.apache.org Requires=network.target remote-fs.target After=network.target remote-fs.target [Service] Type=simple ExecStart=/usr/local/kafka/bin/zookeeper-server-start.sh /usr/local/kafka/config/zookeeper.properties ExecStop=/usr/local/kafka/bin/zookeeper-server-stop.sh Restart=on-abnormal [Install] WantedBy=multi-user.target

ElasticJob achieves distributed coordination through ZooKeeper. In practical scenarios, users may start multiple jobs in the same project simultaneously, all of which use the same Apache Curator client. There are certain risks due to the nature of ZooKeeper and the callback method of Curator in a single event thread.