@ThanhP The following error indicates that Ambari is not able to connect to the MySQL DB instance.
Caused by: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
Most possible cause might be either there is some network issue of your MySQL might not be running properly (running with errors). We might need to review Mysql side log as well.
Checks from AmbariServer Host side
So can you please check if you have entered correct DB url in ambari.properties? Can you please share the following output?
# grep 'jdbc' /etc/ambari-server/conf/ambari.properties
In the output of the above command we shoudl be able to see the MySQL DB details like user/URl/driver ..etc Can you please try running the following simple JDBC connectivity check from Ambari DB host to the MySQL instance?
# /usr/jdk64/jdk1.8.0_112/bin/java -cp /var/lib/ambari-server/resources/DBConnectionVerification.jar:/usr/share/java/mysql-connector-java.jar org.apache.ambari.server.DBConnectionVerification "jdbc:mysql://xxxxxxxxx/ambari" "ambariDBUser" "ambariDBPassword" com.mysql.jdbc.Driver
You will need to change the 'ambariDBUser'/ 'ambariDBPassword' and DB url based on the ambari.properties entries.
Also from the ambari server host can you please check if the MySQL host&port is accessible without any issue? This is to isolate if the MySQL host & port is accessible from Ambari server host?
# telnet $MYSQL_HOSTNAME 3306
(OR)
# nc -v $MYSQL_HOSTNAME 3306
Checks from MySQL DB side
Please try to restart MySQL DB once.
Check if the MySQL is listening to the correct port ? (default port is 3306)
# ps -ef | grep mysql
# netstat -tnlpa | grep 3306
# netstat -tnlpa | grep `cat /var/run/mysqld/mysqld.pid`
For any errors on Mysql side we can check the MySQL log like '# less /var/log/mysqld.log'
