Strangle Your Legacy Code

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

[schmonz.com/talk /2021-oop](https://schmonz.com/talk/2021-oop/)
]

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.left-column[
<a href="https://www.oop-konferenz.de/oop2021/english.html"><img src="./150x77-oop.png" width="150" height="77" alt="OOP Konferenz" class="img" /></a>
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### <a href="https://twitter.com/schmonz">@schmonz</a>

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

[schmonz.com/talk /2021-oop](https://schmonz.com/talk/2021-oop/)
]

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# Strangle Your Legacy Code

## Amitai Schleier

???

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 StranglerFig

## 2. Develop in a real StranglerFig

## 3. Collect learnings
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## [oop-konferenz.de/oop2021 /english /service /code-of-conduct.html](https://www.oop-konferenz.de/oop2021/english/service/code-of-conduct.html)

## 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 figs. 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)
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## 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/Ensemble Programming:

1. Whole team, same problem, same computer

2. Think out loud, together

3. Driver, Navigator, rotate
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- What a mess! We don't know what the _new_ code does
- An extra layer of onion
- Use cases:
    - Could intend to eventually replace legacy, or just make most work easier
    - HTTP reverse proxy
- Techniques:
    - Strangler is like a huge Adapter, or Decorator, or...
    - Either reuse persistence layer, or write an alternate layer and be
      very careful
- Risks:
    - If you hack together too quickly, it's just more mess
    - As an additional layer, could create performance issues
    - As an additional layer, could complicate debugging
    - Might wind up duplicating internal state machine of original legacy code
    - Deployment might be coupled between strangler and original
    - Sometimes a feature can't be fixed in place, needs a Smaller Rewrite
]

---

- [SMTP Strangler](https://github.com/schmonz/smtp-strangler/tree/oop2021) (github.com)
- [Strangler Fig Application](https://www.martinfowler.com/bliki/StranglerFigApplication.html) (martinfowler.com)
- [Legacy Code Rocks](https://www.legacycode.rocks) (legacycode.rocks)
- [Mob Programming Guidebook](http://www.mobprogrammingguidebook.com) (mobprogrammingguidebook.com)
- [Mob Programming RPG](https://github.com/willemlarsen/mobprogrammingrpg) (github.com)
- [PubMob](http://pubmob.com) (pubmob.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/oop21](https://leanpub.com/agilein3minutes/c/oop21)

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)