What is Log4j 2 RCE issue CVE-2021-44228? How to solve Log injection? [Tactical and Permanent Fix]

Hello guys, since the last couple of days, there is a lot of chaos going into the Java world due to the Log4j2 issue which allows Remote code execution (RCE), the CVE-2021-44228, which is designated a zero-day vulnerability. Everyone is busy whether their Java application is impacted and given the popularity of Log4j it's a good chance that your application will be impacted.  Even if you are not using Log4j2 directly, they might be used by the framework or library you use like Spring Boot, Hadoop, Elastic Serach, or Struts. This is kind of a serious issue becuase RCE Vulnarabilyt means it allows hackers to execute code in your servers, and this has been used in past on many breaches like the 2017 Equifax data breach but its not time to lose calm and understand the impact and whether your app is affected or not and what you can do in short term to prevent it. 

How to distinguish logging per Client or Request in Java? Use MDC or Mapped Diagnostic Context in Log4j Example

The MDC or Mapped Diagnostic Context is a concept or feature of the Log4j logging library which can be used to group related log messages together. For example, by using MDC you can stamp a unique identification String like clientId or orderId on each log message, and then by using grep command in Linux, you can extract all log messages for a particular client or order to understand exactly what happened to a particular order. This is especially very useful in multi-threaded, concurrent Java applications where multiple threads are simultaneously processing multiple orders from multiple clients.  In such applications, searching for relevant log messages in a big log file where log messages for multiple orders or clients are overlapping is a big task.