cannot run a distributed MPI program on 2 instances

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I want to run an MPI program on 2 computing nodes, can I create 2 instances and realize it?

I created computing instances "node1" and "node2", the image is Canonical Ubuntu 20.04 Minimal, the shape is VM.Standard2.8. "node1" and "node2" have been configured (e.g., OpenMPI installation, passwordless login between them, a host file "hosts2" containing 2 instances, executable files "test" under the same path of the 2 instances). The MPI program (which is very simple) can be successfully executed on a single instance via $(which mpirun) -n 2 $EXEC_PATH/test. 

Then I ran $(which mpirun) -n 2 -hostfile $HOSTFILE_PATH/hosts2 $EXEC_PATH/test