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I am using aws java sdk to launch EC2 instances (running Ubuntu 12.04) and run a distributed tool on them, the tool uses openMPI for message passing between the nodes and openMPI uses SSH to connect nodes with each other.

The problem is that the EC2 instances don't authenticate each other for SSH connections by default, this tutorial shows how to set up SSH by generating keys and adding them to nodes, However, when I tried to add the generated key to the slaves using the command

$ scp /home/mpiuser/.ssh/id_dsa.pub mpiuser@slave1:.ssh/authorized_keys

I still got permission denied. Also, after generating new keys, I was not able to log in using the ".pem" key that I got from amazon.

I am not experienced with SSH keys, but I would like to have some way of configuring each EC2 instance (when its firstly created) to authenticate the others, for example by coping a key into each of them. Is this possible and how It could be done?

P.S.: I can connect to each instance once it is launched and can execute any commands on them over SSH.

Sami
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1 Answers1

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I found the solution, I added the amazon private key (.pem) in the image (AMI) that I use to create the EC2 instances and I changed the /etc/ssh/ssh_config file by adding a new identity file

IdentityFile /path/to/the/key/file

This made SSH recognize the .pem private key when it tries to connect to any other EC2 instance created with the same key.

I also changed StrictHostKeyChecking to no, which stopped the message "authenticity of host xxx can't be established" which requires users interaction to proceed with connecting to that host.

Sami
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