Strangle Your Legacy Code

.footnote[
### <a href="https://twitter.com/schmonz">@schmonz</a> <a href="https://twitter.com/msilpala">@msilpala</a>

#### <a href="https://twitter.com/hashtag/deliverAgile2019">#deliverAgile2019</a>

[schmonz.com/talk /2019-deliveragile](https://schmonz.com/talk/2019-deliveragile/)
]

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.left-column[
<a href="https://www.agilealliance.org/deliveragile-2019"><img src="./150x134-agile-alliance.jpg" width="150" height="134" alt="deliver:Agile" class="img" /></a>
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### <a href="https://twitter.com/schmonz">@schmonz</a> <a href="https://twitter.com/msilpala">@msilpala</a>

#### <a href="https://twitter.com/hashtag/deliverAgile2019">#deliverAgile2019</a>

[schmonz.com/talk /2019-deliveragile](https://schmonz.com/talk/2019-deliveragile/)
]

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# Strangle Your Legacy Code

## Amitai Schleier Markus Silpala

???

1. Press 'C' to clone and move it to projector
2. Press 'P' to show these here presenter notes

#### How to introduce the problem

- Responsible for production email service
- Keep having to extend it (business, regulatory requirements)
- Look at ofmipd code
- On my 20% time, I had an idea for how to make development easier, cheaper, safer
- Run ofmipd
- Run ofmipd behind env AUTHUP_USER=tim fixsmtpio
- Note the differences?
- We're going to do the same kind of thing, in Python
- Let's run it and say "WORD UP" to the server
- See how that works
- Okay, let's make a new test pass

---

## 1. Introduction to Strangler

## 2. Develop in a real Strangler

## 3. Collect learnings
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---

## [agilealliance.org/code_of_conduct](https://www.agilealliance.org/code_of_conduct/)

## Remind ourselves how we want to behave

## Like TDD, declaring our intentions helps us live up to them
]

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> "One of the natural wonders of [the Queensland coast] are the huge
> strangler vines. They seed in the upper branches of a fig tree and
> gradually work their way down the tree until they root in the soil.
> Over many years they grow into fantastic and beautiful shapes,
> meanwhile strangling and killing the tree that was their host."  
> --[Martin Fowler](https://www.martinfowler.com/bliki/StranglerFigApplication.html)
]

---

## Alternative to Big Rewrite

## Mitigates risk to business

## Likely reduces cost to business
]

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## We're responsible for AcmeCo's email service

## C code from 1998

## We like it, and have invested a lot in it

## But each new feature is expensive to build
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## Mob Programming:

1. Whole team, same problem, same computer

2. Think out loud, together

3. Driver, Navigator, rotate
]

---

- Use cases:
    - Monolith -> microservices (or other arch change)
    - Switch programming language
    - Add logging/telemetry/visibility
    - Eventually retire original system
    - Or just gradually shift focus away
- Techniques:
    - First deploy: no visible change (it's a refactoring!)
    - Migrate feature: call both impls, log if they differ
    - Ship new code under feature flags, just in case
    - For each feature, spike early to validate Strangler
    - Data persistence: reuse old layers, or build new ones very carefully (patterns exist)
    - Delete strangled code as it becomes unused
- Risks:
    - First deploy isn't invisible
    - Old metaphors persist in new codebase
    - New code itself becomes legacy
    - Original goals are eventually forgotten
]

---

- [SMTP Strangler](https://github.com/schmonz/smtp-strangler/tree/deliveragile2019) (github.com)
- [Strangler Application](https://www.martinfowler.com/bliki/StranglerApplication.html) (martinfowler.com)
- [Mob Programming Guidebook](http://www.mobprogrammingguidebook.com) (mobprogrammingguidebook.com)
- [Mob Programming RPG](https://github.com/willemlarsen/mobprogrammingrpg) (github.com)
- [Coding Tour Summer 2018](https://schmonz.com/talk/2018-tour/) (schmonz.com)
]

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## <a href="https://agilein3minut.es/">agilein3minut.es</a>

> "Before Agile in 3 Minutes, I couldn't get my team to have a
> conversation about important topics. Now I have to timebox it."

- <a href="https://agilein3minut.es/8">8: Care</a>
- <a href="https://agilein3minut.es/32">32: Mob</a>
]

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## [leanpub.com/agilein3minutes /c/deliver19](https://leanpub.com/agilein3minutes/c/deliver19)

The simplest _essays_ that could possibly work.
Lowest allowable price on Leanpub, today!
]

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# Strangle Your Legacy Code

## [Amitai Schleier](https://latentagility.com) [Markus Silpala](https://markus.silpala.com/)