Question

Max number of concurrent TCP connections to droplet?

Posted January 10, 2022 105 views
NginxHigh AvailabilityDigitalOcean DropletsBuilding on DigitalOcean

I’m running an api endpoint, and it seems like I’ve hit some droplet limit of 510 or so concurrent connections. 32gig 4 cpu ubuntu 20.04, nginx is optimized. I do have ssl passthrough with a load balancer setup, but only running one droplet under the load balancer while I figure out why the droplet is getting so few connections. I’m running an api service, which will have many thousands of concurrent connections. I have a back end api service, proxy pass to :443. I’m looking a sysctl adjustments now, but that’s my last option to see what’s up with this limit.. my droplet isn’t getting hardly any load during my load tests, if I was getting out of memory errors, I’d be happy, that would mean I’m pushing the server, but I think maybe there is an undisclosed DO rate limit on tcp connections, but there isn’t any documentation I’ve found to support that hypothesis. So I’m posting here to see if anyone has/had a similar situation. I like DO, used it for years. I’m just doing more than websites, and I think I may be trying to exceed the capability of DO.. any help/insight would be helpful. thanks.

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1 answer

I found the issue. on top of the nginx optimizations.. what fixed my low tcp connection issue was tweaking /etc/sysctl.conf

net.ipv4.iplocalportrange = 1024 61000
net.ipv4.tcp
fintimeout=30
net.ipv4.tcp
twreuse=1
net.core.somaxconn=1024
net.core.netdev
maxbacklog=2000
net.ipv4.tcp
maxsynbacklog=2048

Using these resources.
https://stackoverflow.com/questions/410616/increasing-the-maximum-number-of-tcp-ip-connections-in-linux
https://gist.github.com/magnetikonline/2760f98f6bf654d5ad79