Roy's musings

Service health checks are ubiquitous. If you have built any software that relies upon any upstream service, I am sure you would have used some form of health check. Your software could be a stand alone program or it could be a proxy. You may also have built and exposed a service that is used as an upstream service by another software. The worst way to perform health check is to pull a resource (like GET /hc.html, if your service is exposed as a HTTP service) or perform a TCP connect check in the same port where data is served . These are checks I call as in-band health checks .  Please don't do these. Based on my experience, the best way to expose health checks is by using an out-of-band mechanism. This means that you expose another port for performing health check. The client can perform a HTTP check or TCP check in the health check port. As a convenience, if you expose health check as HTTP service in health check port, you can consolidate multiple health checks like: GET /he...

There had been instances when I wanted to copy "/home/roy" to a target directory "/target" as "/target/home/roy". I used to do some scripting foo to get this done. A few days back, I learned this cool option called "--parents" in cp command that will preserve the parent directory structure while copying. Made my life a lot easier on one of my backup tasks.

Today I Learned (TIL) is a series of posts that contain bit sized information that I learned and found to be worthy of sharing with others and keep as a note to myself. For the last couple of years, I had been devoting most of my time in building the start-up, Zycada Networks , that I co-founded. It makes me happy to share my knowledge. So I would like to get back to the habit of writing blog posts regularly on interesting stories, tips-and-tricks, new ideas, technology trends, etc. TIL is one part of doing it.

Sorting numeric values in the input is easy. It just takes "sort -n". But what if the input contains human friendly units. For intance, "5G", "3M", "4K", etc. There is a flag to recognize and sort based on the human friendly units: "-h". Incorrect: du -h | sort -nr Correct: du -h | sort -rh Caveat: "sort -h" works only on upper-case units. "K" will be treated as kilos, but "k" will not be!

Aligning text like a table is often a useful task. I use this workflow to make the text tidier. For instance when I have two columns of text of varying width, aligning them makes it easier to read. Steps: 1) Select the region you would like to align (C-x h will select the entire buffer) 2) C-u M-x align Thats it. The selected region would have been aligned based on the first line of the region. Example: Before: what? who? hello      world After: what? who? hello world By default only the space is used as a delimiter. If you would like to perform a little sophisticated alignment, you can make use of the align-regex function. city, population new york, 8.49M san francisco, 0.85M

Some time back a friend asked me an algorithm question: Given an integer random number generator randomN() that can generate random number in the range [0, N), how will you generate random numbers in the range [0, M) where M I used modulo arithmetic to generate the desired random numbers in the range [0, M). And I reasoned out that if N = q*M + r, every number in the range [0, r] has an occurrence probability of (q+1)/N, but the numbers in the range [r+1, M) has an occurrence probability of only q/N. It is easy to visualize this. See the diagram below: You can see that we can divide line of length N units (given in green) by lines of length M units (given in black). When N is not exactly divisible by M, in the last part alone we have only r units. So if we choose a random integer in the line represented in green, and then take a modulo M on the value, all the values except the values in the range [r+1, M) (represented in red) will occur q+1 times. But the values in that int...