[tor-relays] How to reduce tor CPU load on a single bridge?

Gary C. New garycnew at yahoo.com
Mon Jan 17 22:01:49 UTC 2022

On Monday, January 17, 2022, 11:47:11 AM MST, David Fifield <david at bamsoftware.com> wrote:
 > Gary, I was wondering how you are dealing with the changing onion key issue, and I suppose it is [this](https://forum.torproject.net/t/tor-relays-how-to-reduce-tor-cpu-load-on-a-single-bridge/1483/13):

>> use Source IP Address Sticky Sessions (Pinning)

> The same client source address gets pinned to the same tor instance and therefore the same onion key. If I understand correctly, there's a potential failure if a client changes its IP address and later gets mapped to a different instance. Is that right?

Yes... That is correct. As long as circuits originate from the same Source IP Address, Nginx/HAProxy ensures they are pinned to the same loadbalanced Upstream Tor Node; unless, the originating Source IP Address changes (low-risk) or one of the Upstream Tor Nodes goes down (low-risk with UPS) and surviving circuits migrate to the remaining Upstream Tor Nodes, which effectively forces building of new circuits with relavent keys.
The issue I find more challenging, in loadbalancing Upstream Tor Nodes, is when the Medium-Term Key is updated after running for some time (it's consistent with the previously mentioned 4 - 5 week time period). It is at this point that I notice all circuits bleed-off from the Upstream Tor Nodes with the exception of the Tor Node where the Medium-Term Key was successfully updated. It's at this point that I am forced to shutdown all Upstream Tor Nodes, copy the .tordb containing the updated Medium-Term Key to the other Upstream Tor Nodes, and restart all Upstream Tor Nodes.
If there was a way for a Family of Tor Instances to share a Medium-Term Key, I believe that might solve the long-term issue of running a Loadbalanced Tor Relay.
As it stands... I can run my Loadbalanced Tor Relay for 4 - 5 weeks without any intervention.
Hope that answers your question.

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