Logging Notes

 

Logging Notes

• Logging systems are fast nowadays, no need to use guards (if isXXXEnabled)
• For meaningful logging, override toString in (data) objects
  
• Check actual logs in production/test environments (!)
• Log levels:

    API Request/Response                info
    Main Service entry/exit             info
    Downstream service call/return      info 

    Inside  methods                     debug
    Utility classes                     debug/trace 

    Unrecoverable error                 error
    Recoverable error                   warn

Developer Experience Lessons At Netflix

Netfix provides a great overview on how they operate a huge microservice, serverless stack, including:

• How effortless is the local development experience?
• Are deployment artifacts portable, easy to version and manage?
• What are the implications of increased development velocity
• Can fine-grained functions be composed rapidly with confidence?

Read part1 and part2.  

Issues with Large Scale Microservices

Issues with Large Scale Microservices

• Complexity
• A new feature request modifies multiple services, coordination for
• API
• Protocols
• Development schedule
• Dependency between services → exposing internals
• Running the whole system locally is problematic for developers → setup
• Service Communication
• Direct
• Message middle-ware
• Production Database Access
• Duplicated database
• Write-read-trough 
• Write to a develop database
• Try to read from production database
• If data found → return
• If data not found → read from develop database

Character Encoding Changes in Tomcat 8 for GET Requests

HTTP GET requests (url+parameters) are treated as ASCII characters by default. Non-ASCII values, however, need to be converted to ASCII by using escape sequences. 

This conversion behavior has been changed in Tomcat 8:

• Before Tomcat 8 the default character encoding of the entire GET request was ISO-8859-1, so if your request contains UTF-8 characters (which is very common) you need to manually decode the escaped (ASCII) text back to UTF-8.
  
• Starting with Tomcat 8 the entire GET request is treated as UTF-8 by default but this can be changed to conform with the servlet specification.

Quick and Dirty jstatd Setup on Linux

What is jstatd?

 

"The jstatd tool is an RMI server application that monitors for the creation and termination of instrumented HotSpot Java virtual machines (JVMs) and provides a interface to allow remote monitoring tools to attach to JVMs running on the local host." [source]

NOTE: jstatd is not required for JMX connections;

How to setup jstatd on a Linux server?

A) login as root (told you - it's dirty)

B) create the jstatd.all.policy file in the home folder (/root) with the following content: 

   grant codebase "file:/opt/jdk1.8.0_45/lib/tools.jar" {
       permission java.security.AllPermission;
   };

     NOTE: don't forget to change the path of the JDK

C) run jstatd:

   ./jstatd -p 1099 
     -J-Djava.security.policy=/root/jstatd.all.policy
     -J-Djava.net.preferIPv4Stack=true
     -J-Djava.rmi.server.hostname=172.17.1.143

      -p                                         listen port for jstat daemon 
      java.security.policy             policy file to use (created above)
      java.net.preferIPv4Stack     use IPv4 (optional if IPv6 not used)
      java.rmi.server.hostname    listen on this interface (optional)

      NOTE: add & to run jstatd in background 

D) now you should be able to monitor this server using VisualVM.    

 

Utility Class Using Enum

A utility class using enum:

public enum StringUtil
{
    ;  // enum terminator

    public static void boo ()
    {
        // ...
    }
}

A utility class using class:

public final class StringUtil
{
    public static void boo () {
        // ...
    }

    private StringUtil() {
        // no-init ctor
    }   
}

When using Enum

    ✔ no need for constructor

    ✔ singleton by default

    ✖ automatically extends base Enum class

    ✖ ihnerited Enum methods (name, etc.) available for utility class user

    ✖ Enum static methods (values, etc.) available for utility class user

On-Demand Exporting a Spring Bean via JMX

1) Define the bean to be exported

 <bean id="myBean" class="...." />

2) Define a MBeanExporter

 <bean id="mbeanExporter" class="org.springframework.jmx.export.MBeanExporter" />

2) Get the exporter

 ApplicationContext applicationContext = ...
 MBeanExporter beanExporter = (MBeanExporter) applicationContext.getBean("mbeanExporter");

3) Export the bean

 beanExporter.registerManagedResource(applicationContext.getBean("myBean"), 
                ObjectName.getInstance("com.company:type=Users,name=User-A"));

4) Bean is now accessible via JMX

5) Unregister (if needed)

 beanExporter.unregisterManagedResource (ObjectName.getInstance("com.company:type=Users,name=User-A"));