I recently had an issue with frequent login attempts against one of my services. These were almost all from countries that should not be accessing my service. To resolve the issue I implemented geo-blocking with TCP Wrappers. This is how I went about geo-blocking connections.
(more…)Author: Bill Thorsteinson
Shell Scriptlets
This post will be continually developed. I recently designed some solutions to solve some issues with init.d
(more…)DNS for Email Servers
This article provides a quick overview of the DNS records required for an email server and presents a minimal sample configuration. The example assumes that you are running servers for both email and the web. Comments indicating the changes if you are using a third-party provider are provided.
(more…)Tuning Java Garbage Collection
I recently completed a garbage collection exercise on a variety of applications. In all, twenty WebLogic application clusters were tuned. A dozen of these are large busy application clusters. These provide a mix of Web Applications and Web Services.
Tuning garbage collection is a matter of trade-offs. Large heaps take longer to garbage collect. Small heaps need to be collected frequently using more CPU time.
(more…)Securing TLS
A StackExchange question on using HAProxy’s capture feature to pass data from TCP mode to HTTP mode prompted me to update my SSL configuration. This was intended to get an A+ rating from SSL Labs by sending non-SNI capable clients to a server with weaker ciphers. This was to enable clients on WinXP/IE8, Java 6, and an old Android version to connect. I found a solution without having to have two sets of ciphers and handling traffic in both the TCP mode and HTTP mode. I then optimized my settings to a minimal list of cipher specifications.
(more…)WordPress Tuning
I’ve done a little tuning to my WordPress setup. To keep up to date, I’ve switched from the Ubuntu installation to a downloaded installation under /opt/wordpress. This is owned by my user and served by Apache running as www-data. Updates are done using the SFTP method.
(more…)Command Line Arguments in Python
When I need a new tool, I often code it in Python. Often, command-line options are useful. Sometimes it is possible to have a fixed set of parameters, but this is not very flexible. Fortunately, Python has standard libraries to handle parsing command lines. Three libraries provide varying capabilities. Some of the systems I run on have older versions like Jython 2.1 or Python 2.6. This limits which libraries I can use without backporting libraries
This document provides examples of four command-line processing options. The examples are for a program that processes files and has an optional argument to report the execution time.
(more…)MX on a Dynamic IP Address
I often see posts asking about running a mail server on a Dynamic IP address. Twenty years ago I started running my server on a dynamic IP address. However, times have changed, and it is more difficult to do so. Stil, there are mail server roles that work reasonably well on a dynamic IP address.
(more…)Choosing Log Levels
There are many tools available that will allow a programmer to create log entries. I originally worked with log4j, but have recently been working with logback. I am also working with Jython and am looking at Python’s logging framework. Used well they can make log analysis simple and provide a rich tool for resolving issues. Used poorly they can generate a mass of relatively useless information.
While these loggers have a good hierarchy of levels, the documentation tends to be lacking in guidance on when to use which level. The following document contains the recommendations I have gathered over the years.
(more…)Tuning Linux CPU Performance
A recent kernel change broke my CPU performance tuning. I have an AMD processor that presents 4 cores to the kernel. The process in this article should work for Intel processors although the governors and CPU settings tree may be different. Different kernels may also have different settings. The current kernel allows setting the governor per CPU, but for an earlier kernel, the setting was global.
My system is mostly idle, and I want it to be as quiet as possible. However, from time to time it is busy and I want processing to be as fast as possible. I use a small block of bash code to select a governor and ignore niced programs (such as BOINC) in controlling processor speed.
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