Docker-compose container connection to MySql not working

Question

I'm trying to dockerize an existing java app that uses MySQL database.

The app is supposed to fill the database upon startup. However, when I try to run the app and the database in docker-compose, the app fails to start up due to not being able to connect to the database.

When I try to run the docker-compose, after some time I get this error from the app:

16-Oct-2019 17:28:53.724 INFO [main] com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource. Initializing c3p0 pool... com.mchange.v2.c3p0.PoolBackedDataSource@25010be1 [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@66bb20d8 [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, contextClassLoaderSource -> caller, debugUnreturnedConnectionStackTraces -> false, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceSynchronousCheckins -> false, identityToken -> 1bqsumba51n9qs60y7txqe|66f4fb48, idleConnectionTestPeriod -> 300, initialPoolSize -> 5, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 300, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 50, maxStatementsPerConnection -> 0, minPoolSize -> 5, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@2252819d [ description -> null, driverClass -> null, factoryClassLocation -> null, forceUseNamedDriverClass -> false, identityToken -> 1bqsumba51n9qs60y7txqe|3dc238ae, jdbcUrl -> jdbc:mysql://localhost:3306/db-name, properties -> {password=******, useUnicode=true, handling_mode=DELAYED_ACQUISITION_AND_HOLD, characterEncoding=UTF-8, user=******} ], preferredTestQuery -> null, privilegeSpawnedThreads -> false, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false; userOverrides: {} ], dataSourceName -> null, extensions -> {}, factoryClassLocation -> null, identityToken -> 1bqsumba51n9qs60y7txqe|27551c3a, numHelperThreads -> 3 ]

16-Oct-2019 17:29:24.014 WARNING [C3P0PooledConnectionPoolManager[identityToken->1bqsumba51n9qs60y7txqe|27551c3a]-HelperThread-#1] com.mchange.v2.resourcepool.BasicResourcePool. com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@7a309de0 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception:
com.mysql.jdbc.exceptions.jdbc4.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.
    at jdk.internal.reflect.GeneratedConstructorAccessor29.newInstance(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:377)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1036)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:338)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2232)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2265)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2064)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:790)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
    at jdk.internal.reflect.GeneratedConstructorAccessor26.newInstance(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:377)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:395)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:325)
    at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:175)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125)
    at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
    at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870)
    at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)
Caused by: java.net.ConnectException: Connection refused (Connection refused)
    at java.base/java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.base/java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:399)
    at java.base/java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:242)
    at java.base/java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:224)
    at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:403)
    at java.base/java.net.Socket.connect(Socket.java:591)
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:213)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:297)
    ... 20 more

This is my docker-compose.yml:

version: "2.1"

services:
  app:
    build: .
    expose:
      - 8080
    ports:
      - 8080:8080
    links:
      - database
    depends_on:
      database:
        # waits for database to be ready
        condition: service_healthy

  database:
    image: mysql:latest
    command: --default-authentication-plugin=mysql_native_password
    security_opt:
      - seccomp:unconfined
    environment:
      - MYSQL_ROOT_PASSWORD=root
      - MYSQL_DATABASE=db-name
      - MYSQL_USER=user-web
      - MYSQL_PASSWORD=pass
    expose:
      - 3306
    ports:
      - 3306:3306
    healthcheck:
      # checks whether database is ready
      test: ["CMD", "mysqladmin" ,"ping", "-h", "localhost"]
      timeout: 20s
      retries: 10

The persistence.xml:

...
<!-- JDBC Connection configuration -->
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
<property name="javax.persistence.jdbc.password" value="pass"/>
<property name="javax.persistence.jdbc.user" value="user-web"/>
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/db-name"/>
<property name="hibernate.connection.useUnicode" value="true" />
<property name="hibernate.connection.characterEncoding" value="UTF-8" />
...

I can connect from the host machine to the dockerized database correctly.

Did I get my configuration wrong? Also, is there any way to debug the db connection from the app container?

Answer 1

You should change JDBC url to:

<property name="javax.persistence.jdbc.url" value="jdbc:mysql://database:3306/db-name"/>

Docker-compose connects containers to the default network and service name is the DNS name which will be mapped to container IP.