1.
How to
contribute to
Apache Flink
Robert Metzger
Flink PMC, Software Engineer @ Ververica
rmetzger@apache.org
@rmetzger_

2.
What you will learn today
• What is the Apache Software Foundation
• What are the roles at an Apache project
• How to become a committer
• How to contribute to Apache Flink
• The mailing lists
• The documentation
• Contributing code
• Q & A / Hands-on

3.
Flink and the Apache Software Foundation
• Flink is one of more than 300 top level projects at the ASF
Independent open
source project:
"Stratosphere"
Apache Incubator:
“Apache Flink
(incubating)”
Top level Apache
project
Attic
2009 – 2014 April 2014 – Dec 2014 Since Dec 2014 Hopefully never J

4.
Apache Software Foundation
• Celebrating 20 years of ASF this year
• Initially about Apache HTTP server, “a
patchy server”
• Today, 300+ open source projects (+ 52
incubating)
• 730 members and 7000+ committers
• All volunteer, self-organized, decentralized
• Providing projects with legal and
infrastructure support, and a blueprint
and experience for successful open source
21 founding members
[photo attribution (CC BY) Mark Cox. Tagged image at https://www.flickr.com/photos/iamamoose/63963722/in/album-1381277/ ; gallery at https://www.flickr.com/photos/iamamoose/albums/1381277]
“Community over code”

5.
Apache License 2.0
• Top 3 open source license, used by all ASF projects and many others
• Business friendly (derivative work is allowed to be licensed
differently)
Recommended website: https://tldrlegal.com/license/apache-license-2.0-(apache-2.0)

6.
Roles at the ASF (& Flink)
ASF Members
ASF Board of
directors
Flink PMC Chair
Flink PMC (20) Project Management
Comitee
Flink Committers
(45)
Contributors &
Users
Project oversight: review
releases, long-term health
of project
Permission to commit code,
<user>@apache.org email
Implementation, testing,
documentation, user
support etc.
Day-to-day oversight of
the foundation
Control & “ownership”
members@a.o
board@a.o
private@f.a.o
dev@f.a.o
user@f.a.o
user-zh@f.a.o
commits@f.a.o
issues@f.a.o
public

7.
Becoming a Flink committer: Requirements
• Formally: PMC will vote on a community member to become a
committer (on private@)
• Good contributions over a longer period of time, good technical
oversights and experience (for reviews and discussions)
• Understanding of “The Apache Way”, good community engagement

8.
Contribute to User Support
• user@flink.apache.org (and user-zh@f.a.o) are the primary support
channels: ~150 emails/week. 1000+ subscribers
• Error messages, configuration, API
• Architecture / Design questions
• Stack Overflow
• [apache-flink] tag: 2800 questions,
1100 unanswered
• JIRA (Bug tracker)
• Often, incoming bug reports are ”just” problems
using Flink
Sign up & answer questions

9.
Contribute to
Evangelism
• Meetups
• Speak at your local meetup
• Host a meetup group in your city (Ververica
can help you!)
• Help with venue, organization etc.
• Conferences
• Submit talks at conferences
• Blogs
• Share your experience
• Twitter, LinkedIn, Facebook
• Help spreading the word

10.
Contribute to Flink’s development
• dev@flink.apache.org is the main communication and decision-
making channel of Flink
• Discussion of FLIPs (Flink Improvement Proposals)
• Roadmap planning, release scheduling
• Release voting
• Community health
• All other development and community-related questions (which libraries do
we use, how do we approach large changes)
Join the discussions

11.
Voting: How decisions are being made
• Apache projects vote on: releases, committers, PMC members,
procedural changes, code changes
• +1 / -1, because …
• Most important vote: releases
• Duration of at least 72 hours (workdays)
• Legal checks (checksums, signatures, license documentation) and functional
checks (end to end tests, manual tests, performance)
• See: https://cwiki.apache.org/confluence/display/FLINK/Verifying+a+Flink+Release
• Lazy consensus: Assume consensus after 72 hours, if nobody objects
• Used for smaller changes, procedural changes, ...

12.
Contribute to Flink’s development
• Contribute Documentation (or website)
git clone https://github.com/apache/flink
cd flink/docs/docker
./run.sh
• An easy way to have a lot of impact on Flink
• Jira tickets in component “Documentation” (currently 160
unresolved)
• Small fixes as “[hotfix]” PRs, larger changes through JIRA->PR process
• See also: https://flink.apache.org/contribute-documentation.html

13.
Contribute to Flink’s development: Code
• Contribute code
JIRA Ticket: Get consensus Implement Review Merge
dev@ discussion &
FLIP
Get buy in on your change and find a
committer willing to review and merge
Involved changes often
require a design
document
Reviews happen in pull
requests in a 4-step
process

14.
Contribute to Flink’s development: JIRA
• A good JIRA ticket …
• … is created ahead of time
• ... Clearly describes the problem to solve
• … is assigned to a component, has the right priority
• Get buy-in from a committer … you will need somebody to review and
merge your change later on
• Expect a few days till there’s a first reaction (depending on the
component, complexity) and weeks till there’s consensus

15.
Contribute to Flink’s development: Pull
Request Review
Description
• Formal requirements: JIRA ID in title, description of the change, clean
history (commits prefixed with JIRA ID)
Consensus
• Check if there’s agreement to merge this change as is
• Should not be a problem if JIRA has been “approved”
Architecture
• Architectural fit within Flink
Quality
• Code Quality: documentation, error handling, concurrency / threading,
dependencies

16.
Contribute to Flink’s development: Pull
Request Review: Notes
• Be patient: Reviews take time
• In particular when a release is happening
• Contribute reviews: If you don’t have a feature / fix to contribute,
help checking pull requests in the “quality” stage (see label)
• Stay in touch with the committer managing your contribution

17.
Conclusion
• Introduction on Apache Flink and the ASF
• There are many ways to contribute
• User support
• Project steering
• Evangelism
• Documentation / website
• Code reviews
• Fixes / features
• Even if it sometimes doesn’t seem so: Contributions are very
welcome!
• Reach out to me rmetzger@apache.org / @rmetzger_ if you have
questions

18.
Q & A
Bonus: Hands-on session to help people setting up their development
environments
Robert Metzger
Flink PMC, Software Engineer @ Ververica
rmetzger@apache.org
@rmetzger_