ssh doesnt work at times

asked 2018-04-04 03:59:29 -0500

Deepa gravatar image

updated 2018-04-09 05:55:51 -0500

We do have an Openstack setup (Ocata Version) with 6 hypervisors connected to external Storage using cinder service cpu_allocation_ratio is 1:16 .In certain VM's at times we are facing issue with ssh to its floating IP. If we do a live migrate of that VM to another hypervisor we are able to ssh without any issue What can be the cause ?How can we trouble shoot this further?

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You could be a bit more specific as to your issue. For example: What do you do, what is the result? Do you have basic connectivity (ping)? Is it always the same hypervisor? Do you have connectivity from the VM to the outside world? Does the VM have an IP address?

Bernd Bausch gravatar imageBernd Bausch ( 2018-04-04 04:27:52 -0500 )edit

If you have intermittent connectivity problems, check the connection between the VM and the outside world and use network packet tracing (tcpdump) to find out what's the problem. It depends on your network configuration precisely what you should do.

Bernd Bausch gravatar imageBernd Bausch ( 2018-04-04 04:29:31 -0500 )edit

Thanks Bernd .Its not always the same hypervisor.Yes we do have connectivity from VM to outside world. Yes the VM have internal IP and a floating IP(public).We will be able to ping internal IP when the issue occurs,but floating IP doesn't ping during the issue .

Deepa gravatar imageDeepa ( 2018-04-04 04:44:36 -0500 )edit

We usually identify this issue when we try to ssh .And ping doesn't respond and will get connection time out. We have crossed the original number of CPU.Also how can we use tcpdump if we are unable to ssh to that machine.

Deepa gravatar imageDeepa ( 2018-04-04 04:45:41 -0500 )edit

You can access the machine via its console, but there is a chain of virtual ethernet interfaces, bridges (OVS and/or Linuxbridge), network namespaces, veth pairs etc. between the VM and the outside world, and it's at various points in that chain that you need to trace.

Bernd Bausch gravatar imageBernd Bausch ( 2018-04-04 05:15:57 -0500 )edit