When localhost is not the same as 127.0.0.1 a MySQL Connection Gotcha

Setting up MySQL connection pooling has been standard stuff in server-side apps for as long as I’ve been writing them, so I was at a loss when, every 5 days or so, my newly deployed app died with this exception:

Exception in thread "main" 
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: 
Communications link failure

Last packet sent to the server was 0 ms ago.

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