Simulate high memory usage (in a container)

I wanted a way to simulate high memory usage to test prometheus alerting rules I had defined for high memory usage of containers.

This stackoverflow link shows several ways to simulate high memory usage. I like the following most:

sh -c "MEMBLOB=\$(dd if=/dev/urandom bs=1MB count=256) ; read"

This will increase the memory usage of the shell by 256MB.

How to terminate / kill a TCP connection

Tcpkill is the command (comes with package dsniff)

I have used it to terminate a web-socket connection to a particular worker process, but this can be used to terminate any TCP connection including one on the loopback interface.

Here’s how to identify the active web socket connections nginx has to my backend worker process:

$ sudo netstat -anpo |grep ESTABLISHED | grep  2020 

tcp        0      0 127.0.0.1:2020          127.0.0.1:60895         ESTABLISHED 18567/python     off (0.00/0/0)

tcp        0      0 127.0.0.1:60895         127.0.0.1:2020          ESTABLISHED 15997/nginx: worker off (0.00/0/0)

And here’s the command line to kill the tcp connection:

$ sudo tcpkill -i lo port 60895

tcpkill: listening on lo [port 60895]

127.0.0.1:60895 > 127.0.0.1:2020: R 1232933003:1232933003(0) win 0

127.0.0.1:60895 > 127.0.0.1:2020: R 1232933259:1232933259(0) win 0

127.0.0.1:60895 > 127.0.0.1:2020: R 1232933771:1232933771(0) win 0

127.0.0.1:2020 > 127.0.0.1:60895: R 1218906507:1218906507(0) win 0

127.0.0.1:2020 > 127.0.0.1:60895: R 1218906763:1218906763(0) win 0

127.0.0.1:2020 > 127.0.0.1:60895: R 1218907275:1218907275(0) win 0

127.0.0.1:2020 > 127.0.0.1:60895: R 1218906507:1218906507(0) win 0

127.0.0.1:2020 > 127.0.0.1:60895: R 1218906763:1218906763(0) win 0

127.0.0.1:2020 > 127.0.0.1:60895: R 1218907275:1218907275(0) win 0

^C

Very handy for testing reconnect logic within the application.

NOTE: For tcpkill to work there needs to be some traffic flowing through the connection, so you can start the command then try sending some data.

Check your public IP address using curl or wget

Check your public IP address using curl or wget -

curl -s checkip.dyndns.org | sed -e 's/.*Current IP Address: //' \
       -e 's/<.*$//'  

or

wget http://ipinfo.io/ip -qO -

Courtesy: http://askubuntu.com/questions/95910/command-for-determining-my-public-ip