Lesson 4: Scripting, Troubleshooting, & Workflow

Agenda

• Scripting

  • What's a script?
  • What's a scripting language?
  • Common scripting languages
  • Bash & Python examples

• Troubleshooting

  • Techniques
  • Examples

• Workflow

  • Life cycle of a bug

Scripting

What's a script?

• Piece of code to automate a boring task
• Explanation of how to do what you do

What's a scripting language?

• Compiled vs interpreted

• Expresses logic and actions

  • Logic: loops, conditionals, statements
  • Actions: File I/O, print to console, interact with system utilities

Common Scripting Languages

• Bash
• Python
• Language affects the speed of development and performance of a task
• Most tasks can be done using any language

Bash

• Adds a bit of logic to automate your shell commands
• Saves re-typing things
• Powered by the tools you invoke from the shell
• Scripts can be hard to read at first because they call to external utilities

Python

Why Python?

• Easy to read
• Easy to maintain
• Quick to write
• Lots of libraries

Troubleshooting

Informal method

• Notice that something isn't working right

• Identify what should be happening

  • Define a success criterion ("it works if...")

If it used to work

• Determine what changed

  • Version control history (Git bisect)
  • Emails from the system? Logs? (Check for cron jobs or config mgmt)
  • Ask others who've been working on system

• Use your own notes/documentation

If it's never worked for you

• Determine whether it's possible at all

• Find evidence of similar things working (code, blog posts, stackoverflow)

• If there's no evidence of anything like this working, you might be Doing It Wrong (tm)

• If there's documentation of something similar working:

  • Confirm that the docs are correct for the versions of things that you're using
  • If they docs are wrong, fix them
  • If the docs appear right, figure out what differs between your code and the example

• If there's sample code, make sure you can run it

  • Your goal is minimum viable test case

After finding the problem

• Did the docs tell you how to fix it?

• If you can't fix the problem, identify why not, and then fix that

• Ask for help

  • Expert takes 5 minutes to answer a well-asked question
  • Newbie can waste hours

Formal method

(from this)

• Identify the problem
• Establish a theory of probable cause (question the obvious)
• Test the theory to determine the cause
• Establish a plan of action to resolve the problem and implement the solution
• Verify full system functionality and, if applicable, implement preventative measures
• Document findings, actions, and outcomes

How to get help

• Don't ask to ask
• Summarize what's wrong
• Summarize what you've tried and why it hasn't worked
• Make a specific request, politely
• Pick the right place & time to ask

Documentation

• Man pages

• Wikis

• Google (used wisely)

  • Assessing sites' applicability and reliability

    • Who wrote it?
    • When?
    • Is the other content reliable?
    • Is feedback from others visible? If so, what does it say?

Sources of trouble

Tickets

• Ticket (often sysadmin) or Issue (often developer)

• Ticket comes into tracking system, submitted by a user

• Triage

  • Add details to tickets; consolidate duplicates
  • Contact submitter if more info needed
  • Add tags, milestones, priority, etc.

• Ticket is assigned to someone, who fixes it

• Someone else confirms that the fix works, then ticket is closed

Tickets vs. Issues

• Workflow defined by tracker system

  • RT, Redmine, Chiliproject, GitHub issues, mailing lists

• Issues/Bugs are developer work items which need to be included in a release of code

• Tickets are sysadmin work items, often related to systems improvement or maintenance

• Can't log in because your account got reset: Ticket.

• Can't log in because the newest release of the software is incompatible with the old database format: Bug.

Some Examples

• Trac
• Chiliproject
• RT
• Bugzilla