Linux System Engineering

When you use a variety of languages, such as Java, Ruby, etc., you usually use a framework. There are many different frameworks such as Play(Scala), RoR(Ruby), Spring(Java), etc. You can develop a service with these frameworks, and use a nginx as a reverse proxy. Today, we will see a nginx upstream indicator and about performance. What is nginx upstream? upstream is an indicator that the servers for which nginx receives the request via proxy_pass. The application servers that implement the business logic are in the back of the nginx, and the nginx deliver a user's request to the application servers. the service structure of nginx upstream You can think we can expect a performance degradation, because nginx has steal a user's request, but nginx has many powerful features so it's reasonable to experience a little performace degradation. For examples, to check user-agent for validation check of clients or check referer header values is very difficult to develop in t...

Today's topic is strace, one of the best debugging tools available on Linux. Let's talk briefly about how to use strace and how to utilize them. So, in fact, it can be used in a lot of areas, so what we're dealing with today is basically nothing. Based on this, I hope you will help sole various problems. How to use strace When you see a man page, you see it as shown below. strace - trace system calls and signals Yes. That's right. strace is a debugging tool used to track the system calls and signals used by the application, and to determine if there is no degradation of the performance, and that there is no error in the error. There are several options, but the options that must be used are as follows -s strsize Specify the maximum string size to print (the default is 32) When tracking via strace, set the maximum value for the string to distribute to the screen or file. If you use this value as a default, you will notice that you can not leave ...

If you ask me the most troublesome kernel parameters are for the system engineers, there are probably tcp_tw_reuse and tcp_tw_recycle . These two kernel parameters are looks very similar and it's hard to know difference of two values exactly. So, in this article we will test about these parameters and find out the difference with tcp_tw_reuse and tcp_tw_recycle. Let's start. Materials First of all, prepare two servers. One is the role of client, and the other is the role of server. And in client we set a value of net.ipv4.ip_local_port_range kernel parameter to  32768 32768 . [root@server ~]# sysctl -w "net.ipv4.ip_local_port_range=32768 32768" net.ipv4.ip_local_port_range = 32768 32768 tcp_tw_reuse First, let's test about tcp_tw_reuse . In client, you enter curl command to server. And soon, you will see the port that used to open to server is changed TIME_WAIT state. If you enter curl command again, you will see below error message. tcp_tw_re...