Confluence had failed to start, but we're back up and running again

[Isaac Tien]

My Confluences suddenly  shutdown， after checking the log, I got the warning like: 

2018-12-02 08:10:25,983 WARN [C3P0PooledConnectionPoolManager[identityToken->1bqq1he9zuhn9bn17d32ze|7b072ebd]-HelperThread-#2] [mchange.v2.resourcepool.BasicResourcePool] log com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@4565b236 -- 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: 
java.sql.SQLException: null, message from server: "Host '172.17.0.1' is not allowed to connect to this MySQL server"
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:965)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:898)
 at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:887)
 at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1038)
 at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2190)
 at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2221)
 at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2016)
 at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:776)
 at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
 at sun.reflect.GeneratedConstructorAccessor51.newInstance(Unknown Source)
 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
 at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
 at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
 at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:386)
 at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330)
 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)
2018-12-02 08:10:25,983 WARN [C3P0PooledConnectionPoolManager[identityToken->1bqq1he9zuhn9bn17d32ze|7b072ebd]-HelperThread-#2] [mchange.v2.resourcepool.BasicResourcePool] log Having failed to acquire a resource, com.mchange.v2.resourcepool.BasicResourcePool@421245bc is interrupting all Threads waiting on a resource to check out. Will try again in response to new client requests.

 It seems like something going wrong between the mysql and confluence, but the guy who deployed confluence no longer work with me so could you tell me how can I solve this problem? Thanks!

[Nic Brough -Adaptavist-]

That looks like your MySQL installation has suddenly been reconfigured to stop Confluence connecting to it.

Check that MySQL allows incoming connections locally (the error message says it does not!)

[JP _AC Bielefeld Leader_]

You should also check the error log on the MySQL server: Sometimes MySQL is configured to lock down an IP address if too many connections are aborted and/or used in a specific time frame.