Hey Ho, new blog on hugo and github pages, hoping to post some new content soon.
SYN Cookies & Linux
This started as debugging application timeouts and turned into a deep dive into linux tcp ip stack writing my own netlink query tools. Might be long. Might be rambling. Any comments appreciated. Recently when debugging a timeout issues on a java application, I stumbled upon an interesting problem. The application was making requests to a Loab balancer virtual IP and getting a connection timeout exception in the logs. Unsure of why this was i went poking into nstat counters to see how the LBdealing with all its connections.
rc-local & troubleshooting
Most perf settings in linux can be set from sysctl but there are a few that cant, and i would like to list a few and the best way to apply them. On occassion i have found my rc.local script not executing with upstart on ubuntu 14.04, this can be annoying as usually its executing important performance tweaks. For example readahead on block devices or transparent pages. sudo blockdev --setra 4096 /dev/sda This runs to set readahead on your disks.