My talk at Monki Gras. 2012 Feb, London

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Creating a Developer Community
Kohsuke Kawaguchi
Architect, CloudBees, Inc.

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What is Jenkins?
• Server app for developers
– Called “Continuous Integration server”
• Extensible via plugins
• Easy to get started & configure
jenkins-ci.org

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Jenkins, by the numbers
• 2004 Started as a hobby project
• 2006 2nd committer join the project
• 2008 Jenkins became my day job
• 2012
– 450 releases
– 450+ plugins
– 300+ developers
– 27K installations, 500K users(?)

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Hence my talk today
• How to create a developer community?
– Without any significant resources
• I think I have some recipes to share
– Tried & proven in multiple projects

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Models of OSS projects
• Company-sponsored (JBoss, Spring, etc)
– Dominated by a single entity
– User community, yes, but developer
community?
• Foundation (Apache, Eclipse, etc.)
– Established existing culture, brand, process
• Neither of them work for small projects

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Every developer starts as a visitor
Visitor
User
Developer

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Think about Conversion Funnel
• Visitor to user
– Download, install, initial configuration, …
• User to developer
– Obtain source code, build, run, contribute, …
• Obstacles, however little, add up quickly
• You don’t see the lost opportunities

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Download link? How hard is that…

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But obvious it’s not…

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But obvious it’s not…

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But obvious it’s not…

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But obvious it’s not…

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What to do after download?
• Installation guide
– 31 page PDF
• Quick start guide
– 15 page PDF

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User support
• Great opportunity to convert users to
developers
– Catch them when they are willing to spend
some efforts
– Push source code in front of them

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Make them read code
• Developers tend to forget about this
• Lot can be done to improve experience
– Online browsing
– Source code cross reference
– Aggregate multiple modules
– Better documentation

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Let them hack code
• Is it obvious how to check out code?
• How to build/run/test/debug it?
• Common pitfalls
– Lots of additional pre-requisites
– Non obvious failure mode when you make
mistake

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Modularity
• Your big app needs to be split into pieces
– Pieces that are individually useful
• Why?
– Some people care about one piece but not
your big app
– Every piece reused by one developer gets
100s of users
– It’s a good software engineering anyway

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Programmability
• Every software should be a library
– Let other programs talk to your program
– There’s always a layer above you
• Every one developer building on top of
you = 100s of users
• Don’t work on the same dish
– Split the meal to multiple dishes instead

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Division of labor > Collaboration
• Collaborating on the same code is hard
– Communication is painful
– Time zones aren’t disappearing
– Difference of opinions, practices, & beliefs
– Especially so for faceless OSS collaboration
• Collaboration doesn’t scale
– Every new contributor needs your time

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Therefore, silo is a good thing
• Extensibility (aka plugins)
– e.g., Eclipse, Ant, Maven, Jenkins, …
– Requirement for building a developer
community
• Principles
– Modularity taken to its logical consequences
– Users should see seamless software

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Everyone can claim they’ve got extensibility
• Symptoms of fake extensibility
– One API for internal use, another for plugins
– There are things “core” can do that plugins
can’t
– Features from plugins look different
• Core has to live by the same rules you
impose on plugins

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It works because…
• You don’t see “crappy” code of others
• You don’t need to reject “whacky” ideas
– From time to time other people will prove
you wrong
– Encourages innovations without your making
risky bets
• It’s scalable
– New plugins have ~0 overhead to you
• People feel sense of ownership/stake

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Extensibility alone is not enough
• Center of gravity is needed
– Or else devs will do it in their own caves
– Failed example: Ant
• Benefits
– Sustains the project when people move on
– Grows new core developers
– Enables sharing, reuse, and improvements

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Center of gravity in Jenkins: Update Center
• Mechanism to distribute plugins
– This is how users install them
• In Jenkins, this is tied to source code
hosting
• One commit access for all repositories

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Lowering the barrier to entry
• Remember the funnel
– Make something easy, and get more of them
• In Jenkins, everyone gets a commit
access just by asking
– Akin to Wikipedia
• Encourages small contributions
• Made feasible with silo approach

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Conclusions
• There are many shapes and forms to
OSS projects
– Don’t blindly follow what big guys are doing
• Code is just one piece of puzzle
• Make everything easy, relentlessly
• Bend over backward to make lives easier
for other people