1. "Downloading external resources is disabled." in spring XML

Solution: Window -> Preference -> Maven -> tick the option ('download artifact javadoc')

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I. Setup environment

Ref: https://www.tutorialspoint.com/apache_kafka/apache_kafka_installation_steps.htm

1 - Install Zookeeper

Download Apache Zookeeper : Download

- Upload Zookeeper to /opt

- Unzip installation file:

    $ tar -xzvf apache-zookeeper-3.9.3-bin.tar.gz

- Copy and config file:

    $ cd /bin/conf

    $ cp zoo_sample.cfg zoo.cfg

    $ vi zoo.cfg 

Change dataDir=<path_storage_data>

- Start/Stop ZooKeeper:

$ cd /bin

$ ./zkServer.sh start

$ ./zkServer.sh stop

$ ./zkCli.sh // Connect to Zookeeper server

2. Make Zookeper as Services. (RockyOS 9)

Preapare zookeeper service files:

Ex: zookeeper.service

====================

#!/bin/bash

# chkconfig: 345 80 20

[Unit]

Description=Zookeeper

After=syslog.target network.target

[Service]

Type=forking

ExecStart=/opt/zookeeper/apache-zookeeper-3.9.3-bin/bin/zkServer.sh start

ExecStop=/opt/zookeeper/apache-zookeeper-3.9.3-bin/bin/zkServer.sh stop

User=hqt

Group=hqt

UMask=0007

RestartSec=10

Restart=always

[Install]

WantedBy=multi-user.target

===========================

$  cp /zookeeper.service /usr/lib/systemd/system/

$ systemctl enable zookeeper

$ systemctl daemon-reload

$ systemctl start zookeeper

$ systemctl stop zookeeper

$ systemctl status zookeeper

$chkconfig zookeeper on 

if chkconfig hasn't already existed. Install as below:

$yum install chkconfig

3. Install kafka

Ref: https://kafka.apache.org/quickstart

- Download kafka: Download here

- Upload to server: /opt/kafka

- Unzip file:

$ tar -xzvf kafka_2.13-3.9.0.tgz

- Start/stop kafka:

$ bin/kafka-server-start.sh config/server.properties

$ bin/kafka-server-stop.sh

4. Make Kafka service

$ vi /usr/lib/systemd/system/kafka.service

#!/bin/bash

# chkconfig: 345 80 20

[Unit]

Description=Kafka Service

After=syslog.target network.target

[Unit]

Requires=zookeeper.service

After=zookeeper.service

[Service]

Type=simple

ExecStart=/bin/sh -c '/opt/kafka/kafka_2.13-3.9.0/bin/kafka-server-start.sh /opt/kafka/kafka_2.13-3.9.0/config/server.properties > /opt/kafka/kafka.log 2>&1'

ExecStop=/opt/kafka/kafka_2.13-3.9.0/bin/kafka-server-stop.sh

Restart=on-abnormal

User=hqt

Group=hqt

UMask=0007

RestartSec=10

Restart=always

[Install]

WantedBy=multi-user.target

$ systemctl enable kafka

$ systemctl stat kafka

$ chkconfig kafka on

II. Kafka knowledge

Ref: https://kafka.apache.org/documentation/#gettingStarted

// Create topic

$ bin/kafka-topics.sh --create --topic quickstart-events --bootstrap-server localhost:9092

//Write something to topic

$ ./kafka-console-producer.sh --topic quickstart-events --bootstrap-server localhost:9092

//Read content of topic

$ ./kafka-console-consumer.sh --topic quickstart-events --from-beginning --bootstrap-server localhost:9092

Write "hello" to the topic:

Read content from the topic:

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