Scenario: A JDK8 Docker container using OJDBC7 to connect to the database. Sounds simple enough, what could go wrong?
Simptoms: Connecting to the database randomly takes several minutes, fails with a weird SqlRecoverableException: no more data to read from socket or just works fine as if there is no problem.
The same Docker image also works fine on some machine but fails consistently on other.
The reason is this. Docker is not good at /dev/random. Probably even more so if you run it in a VM, since it’s double isolated from actual entropy sources (my non scientific observation). For whatever reason, OJDBC defaults to /dev/random and this causes a block when connecting to the database due to high probability of /dev/random depletion.
Simple solution is to just mount /dev/urandom to /dev/random inside the Docker, in docker run command:
-v /dev/urandom:/dev/random
So.. if you ever want to use OJDBC inside Docker, remember this flag. It will save lives or at least spare you hours of useless debugging.
Cen