noahlz

Troubleshooting Production JVMs with jcmd

jcmd is a powerful new tool introduced in Java 7. Along with jstack and jps, it should be in your go-to tool for solving production problems on the JVM. (Come to think of it, with this tool you don't really need jps anymore)

Here's an example session with jcmd:

$ ssh wopr.qa.corp.local
$ jcmd -l
34739 sun.tools.jcmd.JCmd -l

noahlz

Operations Team should not deploy a new software application to production unless the Development Team complies with the following minimum requirements:

Software Requirements

• Packaging: the application must conform to conventions for configuration, directory structure and run scripts:

  • Configuration
  • Deployment Build
  • Run script

• Reference Configuration: The reference configuration file included in the package must:

noahlz

Here's my idea of what goes in a run book for an application:

• On which servers it is installed
• Databases to which it connects (externally managed, not embedded)
• how to start/stop, i.e. actual command line or script to execute
• Scheduled batch jobs / EOD processes. Not the actual schedule, but when they generally run (EOD, overnight, etc)
• Where to find log files
• How to verify that it's actually running
• A screen shot of the login page and one or two application pages is helpful.

noahlz

trait Color {
  def name: String
}

abstract class PrimaryColor(val name: String) extends Color
case object Red extends PrimaryColor("Red")
case object Blue extends PrimaryColor("Blue")
case object Yellow extends PrimaryColor("Yellow")

trait HasColors {

noahlz

Scala can be a little obtuse. Yesterday I encountered something like this:

def foo(bar: Bar): Option[Bazz => Buzz => Blah]

It's a function that takes Bar and returns an Option boxing a function that takes a Buzz and returns a Blah. I think some clarifying parenthesis are in order, and probably should be required by the compiler.

When you see something like this:

noahlz

(ns hello.core
  (:require [clojure.java.io :as io])
  (:import [java.net ServerSocket]))

;; Server
(defn receive-msg [socket]
  (.readLine (io/reader socket)))

(defn send-msg [socket msg]
  (let [writer (io/writer socket)]

noahlz

def divBy3(x: Int)  = x % 3 == 0
// divBy3: (x: Int)Boolean

def divBy5(x: Int)  = x % 5 == 0
// divBy5: (x: Int)Boolean

def divByAll(fns: List[(Int => Boolean)])(x: Int) = fns.foldLeft(true)((modZero, fn: (Int => Boolean)) => modZero && fn(x))
// divByAll: (fns: List[Int => Boolean])(x: Int)Boolean

val divBy3And5 = divByAll(List(divBy3,divBy5)) _

noahlz

// See http://stackoverflow.com/questions/1052476/what-is-scalas-yield/1059501#1059501

// Compilation error is:
// [error]  found   : Seq[String]
// [error]  required: Option[?]
// [error]     child <- foo.children
// [error]           ^
// [error] one error found

noahlz

# http://stackoverflow.com/questions/6012665/read-non-blocking-error-while-using-pxssh-ssh-module-for-python
# https://github.com/paramiko/paramiko/blob/master/README
# http://stackoverflow.com/questions/8491194/how-to-handle-socket-errors-as-exceptions-in-python-paramiko

import paramiko, base64, getpass, socket

client = paramiko.SSHClient()
client.set_missing_host_key_policy(paramiko.AutoAddPolicy())

user = getpass.getuser()

noahlz

// Welcome to Scala version 2.9.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_15).
// Type in expressions to have them evaluated.
// Type :help for more information.

def foo(n: Int) = Some(n)
// foo: (n: Int)Some[Int]

List(1,2,3,4).map(foo(_))
// res2: List[Some[Int]] = List(Some(1), Some(2), Some(3), Some(4))