Strangle Your Legacy Code

[schmonz.com/talk<br />/2020-minispa](https://schmonz.com/talk/2020-minispa/)

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

<a href="https://www.bcs.org/events/2020/february/mini-spa-conference-2020-leeds/"><img src="./65x81-bcslogo.png" width="65" height="81" alt="Mini-SPA Conference 2020" class="img" /></a>
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[schmonz.com/talk<br />/2020-minispa](https://schmonz.com/talk/2020-minispa/)

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

<a href="https://www.bcs.org/events/2020/february/mini-spa-conference-2020-leeds/"><img src="./65x81-bcslogo.png" width="65" height="81" alt="Mini-SPA Conference 2020" class="img" /></a>
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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

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## 1. Introduction to Strangler

## 2. Develop in a real Strangler

## 3. Collect learnings
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## [spaconference.org/spa2020<br />/code-of-conduct.html](https://www.spaconference.org/spa2020/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 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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## Lower cost than Infinite Refactoring

## Lower risk than The Big Rewrite
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## We're responsible for AcmeCo's email service

## Well-architected but idiosyncratic 1998 C

## We've happily invested a lot in it

## Could marginal cost of features be lower?
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## To the IDE!
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## Monolith -> microservices

## Switch programming language

## Add logging/telemetry/visibility

## Eventually retire original system

## Or just gradually shift focus away
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## First deploy: no visible change

## Data persistence: reuse legacy layer or route around it

## Migrate feature: call both impls, log diffs

## New feature: ship under feature flag

## Incrementally delete strangled code and data
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## First deploy is visible

## Data accessed and/or stored two ways

## Architecture gets complexicated

## Old metaphors persist in new code

## Old skills create new legacy code

## Original goals forgotten over the years
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## [SMTP Strangler](https://github.com/schmonz/smtp-strangler/tree/minispa2020) (github.com)

## [Strangler 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)
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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<br />/c/minispa20](https://leanpub.com/agilein3minutes/c/minispa20)

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)