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First of all, let's try to connect to the computing services via SSH:

Accessing a login node

1. Access the default login node of the ATOS HPCF or ECS and take note of what node you are in 

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   title Solution - HPCF
   No Format ssh hpc-login hostname

   
   

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   title Solution - ECS
   No Format ssh ecs-login hostname

   
   

2. Open a new tab in your terminal and connect again. Did you get the same hostname? Why is that?

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   title Answer
   hpc-login hostname is an alias to a load-balanced service of login nodes. You may land on a different one every time you connect. ecs-login is an alias to a specific login node of the ECS virtual cluster. It is not automatically load-balanced, so you will typically land on the same node on consecutive connections. Both aliases will always point to a working login node, and the actual node and complex behind it may change depending on the load, system sessions or outages.

   
   

3. Now, from your open SSH session on Atos HPCF or ECS, connect to the main login alias again. Did it ask for a password? Can you set your account up so jumps between hosts are done without a password?

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   title Answer
   Password-less SSH between ECMWF hosts such as Atos HPCF or ECS nodes, or VDI hosts is not set up by default. If you were asked for a password, you can run the following command from your Atos HPCF, ECS or VDI session to set up  key-based authentication: No Format ssh-key-setup After this you should be able to jump between hosts without having to introduce your password. Besides being convenient, this setup is also necessary for other tools such as ECACCESS or ecinteractive to work properly.

   
   

Interactive session

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