Unable to Connect MySQL container to Tomcat Container in docker

Question

The Plan

I want my tomcat server to be able to connect to my MySQL server both in separate containers.

The Problem

Tomcat cannot connect to MySQL

I used some of the details from the wordpress tutorial about setting up a link with the mysql container and created the link to the MySQL.

Although the tomcat and mysql spin up just fine I can't seem to get tomcat to be able to connect to MySQL, the settings work on my local machine perfectly fine.

I've attempted to use --net: "host" as well although that does not work with Tomcat as it throws a severe error.

Previous answers

I noticed on this post a load of possible fixes for the error although I don't believe any of these would translate to my problem as I believe this is a docker problem not a host one.

docker-compose.yml

web:
  image: tomcat:7.0
  container_name: tomcat-container
  ports:
   - "80:8080"
  hostname: docker-tomcat
  volumes:
   - /home/webapps:/usr/local/tomcat/webapps
  links:
   - db
db:
  image: mysql
  container_name: mysql-container
  environment:
   MYSQL_ROOT_PASSWORD: Mysqlpassword1
   MYSQL_DATABASE: tracker
  volumes:
   - /home/mysqlDB:/var/lib/mysql

This is my Context.xml from tomcat.

<Context>
    <Resource
        name="jdbc/tracker" type="javax.sql.DataSource"
        maxActive="100" maxIdle="30" maxWait="10000" 
        url="jdbc:mysql://localhost:3306/tracker?useSSL=false"
        driverClassName="com.mysql.jdbc.Driver"
        username="root" password="mysqladmin1"
    />
    <Resource
        name="jdbc/jenkins" type="javax.sql.DataSource"
        maxActive="100" maxIdle="30" maxWait="10000" 
        url="jdbc:mysql://localhost:3306/jenkins?useSSL=false"
        driverClassName="com.mysql.jdbc.Driver"
        username="root" password="mysqladmin1"
    />
</Context>

The error code.

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:1549)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1388)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
at databaseConnections.SQLDatabaseConnection.tableExists(SQLDatabaseConnection.java:131)
at databaseConnections.JiraSQLDatabaseConnection.<init>(JiraSQLDatabaseConnection.java:50)

Answer 1

As you're linking db as "db", you cannot use localhost to join you database. you should "db"

jdbc:mysql://db:3306/tracker?useSSL=false

In your container, localhost design your tomcat container, not your host. MySQL container has his own network.

Futhermore, if you don't like "db" name, you can name link it with different name

For exemple:

 links:
   - db:container-mysql

In this case, inside you tomcat container, you could use

jdbc:mysql://container-mysql:3306/tracker?useSSL=false

Answer 2

If you are using a container already running or run by using separate DockerFile, then you might want to consider using

external_links:
  -  mysql-container:db

Note that the name mysql-container is the name of your container. If you don't know the name or haven't specified one in the docker-compose.yml you can also find it by running

docker ps

The column with the NAMES is the one you'll need in the external links. The db after : is just an alias and it could be anything you want. It will be your hostname. For example if before dockerizing the database your host was localhost you have to now change it into db.

Lastly, you must also be sure to have both of the containers running in the same network. You can do that by creating a new network as:

docker network create --driver=bridge my-network

Then inside the docker-compose.yml of both the containers, add the following network configuration at the same indentation level as that of service

networks:
  default:
    external:
      name: my-network