Strangle Your Legacy Code

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[schmonz.com/talk<br />/2018-newcastle](https://schmonz.com/talk/2018-newcastle/)
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# Strangle Your Legacy Code

## Amitai Schleier

### 2018/08/15

???

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

### 75 minutes

When you're mired in an ancient codebase that makes refactoring risky
and expensive, how do you clear a path to continued delivery? According
to the old saw, the best time to plant a tree is 20 years ago, and the
next best time is today. But if you already have a gnarled old source
tree, an old saw is the wrong tool. Instead, plant a Strangler: a
pattern for preserving your software investment by arranging for new
functionality to grow in a new codebase.

As a mob, we'll take a quick look at a Strangler, then test-drive new
features into it. Don't know what to try next? Take the keyboard. Got an
idea? Step away and talk someone else through it. You'll leave with a
powerful strategy for extending the useful life of working, valuable
software -- *especially* when it's hard to change. We'll also send you
home with a free bonus development practice to accelerate your team's
learning. For a limited time only!

### 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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## Is there one for this meetup?

## 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)
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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

## Say goodbye to these slides!

## [github.com/schmonz/smtp-strangler](https://github.com/schmonz/smtp-strangler/tree/nebytes)
]

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- None of this was .NET!
- Nice to try some Python
- This was _not_ a realistic example of Mob Programming
    - Way too much Amitai navigating
- Strangler pattern applicable at work for at least one of you
- Useful to understand the business case for Strangler, when to choose it
- Feels similar to how we wrap dependencies with the Adapter pattern
- A potentially safe mechanism to intervene in legacy code (a la [Feathers](https://amzn.to/2KXKqjR))
- Strangler is labor-intensive; don't use it unless the alternative is worse
]

---

- [SMTP Strangler](https://github.com/schmonz/smtp-strangler) (github.com)
- [Strangler Application](https://www.martinfowler.com/bliki/StranglerApplication.html) (martinfowler.com)
- [Mob Programming Guidebook](https://leanpub.com/mobprogrammingguidebook) (leanpub.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<br />/c/nebytes18](https://leanpub.com/agilein3minutes/c/nebytes18)

The simplest _essays_ that could possibly work.
Lowest allowable price on Leanpub, today!
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# Strangle Your Legacy Code

## Amitai Schleier

## [latentagility.com](https://latentagility.com)