OpenJDK CentOS 8.2 Datadog Monitoring

Comprehensive guide for installing, configuring, and monitoring OpenJDK applications on CentOS 8.2 with Datadog agent integration.

Prerequisites

System Requirements

cat /etc/redhat-release

uname -r

free -h

df -h

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OpenJDK Installation

1. Check Available OpenJDK Versions

dnf list java*openjdk*

dnf search openjdk

alternatives --display java

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2. Install OpenJDK 8

sudo dnf install java-1.8.0-openjdk

sudo dnf install java-1.8.0-openjdk-devel

sudo dnf install java-1.8.0-openjdk-headless

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3. Install OpenJDK 11

sudo dnf install java-11-openjdk

sudo dnf install java-11-openjdk-devel

sudo dnf install java-11-openjdk-headless

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4. Install OpenJDK 17

sudo dnf install java-17-openjdk

sudo dnf install java-17-openjdk-devel

sudo dnf install java-17-openjdk-headless

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Java Environment Configuration

5. Set Default Java Version

sudo alternatives --config java

sudo alternatives --config javac

sudo alternatives --install /usr/bin/java java /usr/lib/jvm/java-11-openjdk/bin/java 1

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6. Configure JAVA_HOME

echo 'export JAVA_HOME=/usr/lib/jvm/java-11-openjdk' >> ~/.bashrc

echo 'export PATH=$JAVA_HOME/bin:$PATH' >> ~/.bashrc

source ~/.bashrc

echo $JAVA_HOME

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7. Verify Java Installation

java -version

javac -version

which java

readlink -f $(which java)

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JVM Monitoring Setup

8. Enable JMX for Monitoring

java -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=9999 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -jar your-app.jar

java -Dcom.sun.management.jmxremote.port=9999 -Dcom.sun.management.jmxremote.rmi.port=9999 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Djava.rmi.server.hostname=localhost -jar your-app.jar

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9. JVM Memory Configuration

java -Xms512m -Xmx2g -XX:+UseG1GC -jar your-app.jar

java -Xms1g -Xmx4g -XX:+UseParallelGC -XX:+UseParallelOldGC -jar your-app.jar

java -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -Xloggc:/var/log/gc.log -jar your-app.jar

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Datadog Agent Configuration

10. Install Datadog Agent

DD_AGENT_MAJOR_VERSION=7 DD_API_KEY=your_api_key DD_SITE="datadoghq.com" bash -c "$(curl -L https://s3.amazonaws.com/dd-agent/scripts/install_script.sh)"

sudo systemctl enable datadog-agent

sudo systemctl start datadog-agent

sudo systemctl status datadog-agent

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11. Configure JMX Integration

sudo cp /etc/datadog-agent/conf.d/jmx.d/conf.yaml.example /etc/datadog-agent/conf.d/jmx.d/conf.yaml

sudo vim /etc/datadog-agent/conf.d/jmx.d/conf.yaml

JMX Configuration Content:

init_config:
  is_jmx: true
  collect_default_metrics: true

instances:
  - host: localhost
    port: 9999
    tags:
      - env:production
      - service:java-app

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12. Configure Java Integration

sudo cp /etc/datadog-agent/conf.d/java.d/conf.yaml.example /etc/datadog-agent/conf.d/java.d/conf.yaml

sudo vim /etc/datadog-agent/conf.d/java.d/conf.yaml

Java Integration Configuration:

init_config:

instances:
  - host: localhost
    port: 9999
    name: java-app
    tags:
      - env:production
      - java_version:11

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13. Restart Datadog Agent

sudo systemctl restart datadog-agent

sudo systemctl status datadog-agent

sudo datadog-agent status

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Java Application Monitoring

14. Check Java Processes

ps aux | grep java

jps -v

jps -l

pgrep -f java

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15. Monitor JVM Memory Usage

jstat -gc $(pgrep java) 1s

jstat -gcutil $(pgrep java) 5s

jmap -heap $(pgrep java)

jmap -histo $(pgrep java) | head -20

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16. Monitor JVM Thread Usage

jstack $(pgrep java)

jstack $(pgrep java) | grep "java.lang.Thread.State" | sort | uniq -c

top -H -p $(pgrep java)

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17. JVM Performance Analysis

jstat -compiler $(pgrep java)

jstat -class $(pgrep java)

jcmd $(pgrep java) VM.uptime

jcmd $(pgrep java) VM.system_properties

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Log Configuration

18. Configure Java Application Logging

java -Djava.util.logging.config.file=logging.properties -jar your-app.jar

java -Dlogback.configurationFile=logback.xml -jar your-app.jar

java -Dlog4j.configuration=log4j.properties -jar your-app.jar

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19. Datadog Log Collection

sudo vim /etc/datadog-agent/conf.d/java.d/conf.yaml

Add logging configuration:

logs:
  - type: file
    path: "/var/log/java/application.log"
    service: "java-app"
    source: "java"
    sourcecategory: "sourcecode"
    tags:
      - env:production

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20. Enable Log Collection

sudo vim /etc/datadog-agent/datadog.yaml

Enable logs:

logs_enabled: true

sudo systemctl restart datadog-agent

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Performance Monitoring

21. CPU and Memory Monitoring

top -p $(pgrep java)

htop -p $(pgrep java)

pidstat -p $(pgrep java) 1

iostat -x 1

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22. Network Monitoring

ss -tulnp | grep java

netstat -tulnp | grep java

lsof -i -P | grep java

tcpdump -i any port 8080

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23. File Descriptor Monitoring

lsof -p $(pgrep java) | wc -l

cat /proc/$(pgrep java)/limits | grep "Max open files"

ls -la /proc/$(pgrep java)/fd | wc -l

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Health Checks

24. Application Health Checks

curl -f http://localhost:8080/health

curl -s http://localhost:8080/actuator/health | jq

curl -s http://localhost:8080/metrics | grep jvm

wget --spider -q http://localhost:8080/health && echo "OK" || echo "FAIL"

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25. JMX Health Monitoring

jconsole localhost:9999

jcmd $(pgrep java) GC.run

jcmd $(pgrep java) VM.classloader_stats

jcmd $(pgrep java) Thread.print

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Troubleshooting

26. Common Java Issues

jcmd $(pgrep java) VM.flags

jinfo $(pgrep java)

jmap -dump:format=b,file=/tmp/heapdump.hprof $(pgrep java)

kill -3 $(pgrep java)

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27. Datadog Agent Debugging

sudo datadog-agent status

sudo datadog-agent check jmx

sudo datadog-agent check java

sudo tail -f /var/log/datadog/agent.log

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28. JMX Connection Testing

telnet localhost 9999

nc -zv localhost 9999

jcmd $(pgrep java) ManagementAgent.status

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Security Configuration

29. JMX Security Setup

java -Dcom.sun.management.jmxremote.password.file=/path/to/jmxremote.password -Dcom.sun.management.jmxremote.access.file=/path/to/jmxremote.access -jar your-app.jar

Create password file:

echo "monitor readonly" > /etc/java/jmxremote.password

echo "control readwrite" >> /etc/java/jmxremote.password

chmod 600 /etc/java/jmxremote.password

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30. Firewall Configuration

sudo firewall-cmd --permanent --add-port=9999/tcp

sudo firewall-cmd --permanent --add-port=8080/tcp

sudo firewall-cmd --reload

sudo firewall-cmd --list-ports

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Automated Monitoring Scripts

31. Java Process Monitor Script

#!/bin/bash
# java_monitor.sh
JAVA_PID=$(pgrep java)
if [ -z "$JAVA_PID" ]; then
  echo "Java process not running"
  exit 1
fi

echo "Java PID: $JAVA_PID"
echo "Memory Usage:"
jstat -gc $JAVA_PID 1 1
echo "Thread Count:"
jstack $JAVA_PID | grep "java.lang.Thread.State" | wc -l

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32. Health Check Script

#!/bin/bash
# health_check.sh
APP_URL="http://localhost:8080/health"
RESPONSE=$(curl -s -o /dev/null -w "%{http_code}" $APP_URL)

if [ $RESPONSE -eq 200 ]; then
  echo "Application healthy"
  exit 0
else
  echo "Application unhealthy: HTTP $RESPONSE"
  exit 1
fi

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33. GC Log Analysis

tail -f /var/log/gc.log | grep "Full GC"

awk '/Full GC/ {print $1, $2, $NF}' /var/log/gc.log

grep "Total time for which application threads were stopped" /var/log/gc.log

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Performance Tuning

34. JVM Tuning Parameters

java -XX:+UseG1GC -XX:MaxGCPauseMillis=100 -XX:G1HeapRegionSize=16m -jar your-app.jar

java -XX:+UseConcMarkSweepGC -XX:+CMSParallelRemarkEnabled -XX:+UseCMSInitiatingOccupancyOnly -XX:CMSInitiatingOccupancyFraction=70 -jar your-app.jar

java -XX:+UnlockExperimentalVMOptions -XX:+UseZGC -jar your-app.jar

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35. Memory Optimization

java -XX:NewRatio=3 -XX:SurvivorRatio=8 -jar your-app.jar

java -XX:+UseStringDeduplication -jar your-app.jar

java -XX:+UseCompressedOops -XX:+UseCompressedClassPointers -jar your-app.jar

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Monitoring Dashboard Setup

36. Custom Metrics Collection

Create custom metrics configuration:

# /etc/datadog-agent/conf.d/jmx.d/conf.yaml
init_config:
  is_jmx: true

instances:
  - host: localhost
    port: 9999
    conf:
      - include:
          domain: java.lang
          type: Memory
          attribute:
            HeapMemoryUsage.used:
              alias: jvm.heap_memory.used
              metric_type: gauge
            HeapMemoryUsage.max:
              alias: jvm.heap_memory.max
              metric_type: gauge

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37. Application Performance Monitoring

java -javaagent:/opt/datadog/dd-java-agent.jar -jar your-app.jar

export DD_SERVICE_NAME="java-app"

export DD_ENV="production"

export DD_VERSION="1.0.0"

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Quick Reference Commands

38. Essential Java Commands

java -version

ps aux | grep java

jps -v

jstat -gc $(pgrep java)

jstack $(pgrep java)

jmap -heap $(pgrep java)

sudo systemctl status datadog-agent

sudo datadog-agent status

curl http://localhost:8080/health

telnet localhost 9999

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Quick Reference Table

Task	Command
Check Java version	java -version
List Java processes	jps -v
Monitor GC	jstat -gc $(pgrep java)
Thread dump	jstack $(pgrep java)
Heap dump	jmap -dump:file=heap.hprof $(pgrep java)
Datadog status	sudo datadog-agent status
Check JMX	telnet localhost 9999
Application health	curl http://localhost:8080/health
GC logs	tail -f /var/log/gc.log
Memory usage	jmap -heap $(pgrep java)
JVM flags	jcmd $(pgrep java) VM.flags
Thread analysis	jstack $(pgrep java) | grep State | sort | uniq -c

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Related Documentation

• Datadog Agent Setup - Datadog agent installation
• Service Management - Systemctl service commands
• Proxy Configuration - Datadog proxy setup
• Proxy Testing - Network diagnostics