Com.MySQL.Jdbc.Exceptions.Jdbc4.Communicationsexception: Communications Link Failure

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

So, you have a

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

java.net.ConnectException: Connection refused

I'm quoting from this answer which also contains a step-by-step MySQL+JDBC tutorial:

If you get a SQLException: Connection refused or Connection timed out or a MySQL specific CommunicationsException:
Communications link failure, then it means that the DB isn't reachable at all. This can have one or more of the following causes:

1. IP address or hostname in JDBC URL is wrong.
2. Hostname in JDBC URL is not recognized by local DNS server.
3. Port number is missing or wrong in JDBC URL.
4. DB server is down.
5. DB server doesn't accept TCP/IP connections.
6. DB server has run out of connections.
7. Something in between Java and DB is blocking connections, e.g. a firewall or proxy.
   
   
   

To solve the one or the other, follow the following advices:

1. Verify and test them with ping.
2. Refresh DNS or use IP address in JDBC URL instead.
3. Verify it based on my.cnf of MySQL DB.
4. Start the DB.
5. Verify if mysqld is started without the --skip-networking option.
6. Restart the DB and fix your code accordingly that it closes connections in finally.
7. Disable firewall and/or configure firewall/proxy to allow/forward the port.
   
   
   

See also:

• How should I connect to JDBC database / datasource in a servlet based application?
• Is it safe to use a static java.sql.Connection instance in a multithreaded system?

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

So, you have a

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

java.net.ConnectException: Connection refused

I'm quoting from this answer which also contains a step-by-step MySQL+JDBC tutorial:

If you get a SQLException: Connection refused or Connection timed out or a MySQL specific CommunicationsException:
Communications link failure, then it means that the DB isn't reachable at all. This can have one or more of the following causes:

1. IP address or hostname in JDBC URL is wrong.
2. Hostname in JDBC URL is not recognized by local DNS server.
3. Port number is missing or wrong in JDBC URL.
4. DB server is down.
5. DB server doesn't accept TCP/IP connections.
6. DB server has run out of connections.
7. Something in between Java and DB is blocking connections, e.g. a firewall or proxy.
   
   
   

To solve the one or the other, follow the following advices:

1. Verify and test them with ping.
2. Refresh DNS or use IP address in JDBC URL instead.
3. Verify it based on my.cnf of MySQL DB.
4. Start the DB.
5. Verify if mysqld is started without the --skip-networking option.
6. Restart the DB and fix your code accordingly that it closes connections in finally.
7. Disable firewall and/or configure firewall/proxy to allow/forward the port.
   
   
   

See also:

• How should I connect to JDBC database / datasource in a servlet based application?
• Is it safe to use a static java.sql.Connection instance in a multithreaded system?

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

This is more a docker question than a MySQL/JDBC connections. Your second docker container can't reach your first because the 127.0.0.1 there points to the container itself, and not the first container.

First of all, you shouldn't configure the bind_address in the first container to be 127.0.0.1. You either need to leave it out or set it to 0.0.0.0. You probably didn't restart MySQL, otherwise you wouldn't have been able to connect from MySQL Workbench on your own machine either.

The ability to connect through 127.0.0.1 from your machine to an application running within docker is only available on your machine, not between containers.

Your command line shows you linked the myApp container to the mysql container (using --link mysql). That means that as the connection URL you should use:

jdbc:mysql://mysql:3306/mydatabase

That is: replace 127.0.0.1 with mysql as that is used as the host name of your mysql container to communicate between those two containers.

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