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How To Start Improving a Legacy App

An interesting question appeared on HN recently: “Ask HN: Inherited the worst code and tech team I have ever seen. How to fix it?

You can read that post and the answers there. I’m going to address a related, but different question in this post.

If you run encounter an application that has tremendous business value and yet is not following any modern software management processes, what are concrete steps you can take to help improve the application?

That is, what if you have (or are hired to be responsible  for) an app like the poster of the HN thread:

  • making plenty of money for the company
  • no version control
  • old school structure
  • a ball of mud architecture
  • no code deleted, just commented out
  • multiple versions of libraries on the front and back end
  • etc

First off, you need to convince someone that it is going to be worthwhile to invest in this process. If you can’t do that, you are dead in the water. So look for the pain points that occur when best practices are lacking:

  • slow delivery of features
  • catastrophic bugs which lose money, hurt the brand or impact data
  • talent hard to hire
  • hard to improve the application

If you can pinpoint pain caused by the app, you can start to build a case to improve it.

If you can’t, well then, maybe you shouldn’t touch it. If it ain’t broke, don’t fix it!

With that said, here’s my list of what to implement, in rough priority order. Don’t worry about best of breed for the tools, just pick what the company uses. If the tool isn’t in use at the company, pick something you and the team are familiar with. If there is nothing in that set, pick the industry standard. I include a recommendation for the latter.

1. Get the app under version control. Git is best if you don’t have any existing solution. GitHub or GitLab are great places to store your git repositories.

2. Start up a bug tracker. You have to have a place to keep track of all issues. GitHub issues is adequate, but there are a ton of options. This would be an awesome place to get buy-in from the existing team about whichever one they prefer. The truth it is doesn’t matter which particular bug tracker you use, just that you use one.

3. A way to get one click or zero click deploys. A SaaS tool like CircleCI, GitHub actions is fine. If you require “on prem”, Jenkins is a fine place to start. But you want to be able to deploy changes quickly.

4. Set up a staging environment. With one, you can manually test changes and debug issues without affecting production. Building this will also give you confidence that you understand how the system is deployed. Then you can can include that in the build tool process.

5. Unit and system/end to end testing. End to end testing can give you confidence in changes. However, it is overwhelming to add testing to an existing large, crufty codebase. I’d focus on two things: unit testing some of the weird logic; this is a relatively quick win. Second, setting up at least one or two end to end tests through core flows (login, purchase path, etc). In my experience, setting up the first instance of each of these is the toughest process, then it gets progressively easier. There’s usually an ‘xUnit’ framework in any language for unit testing. Look for that. I’m not sure what best practice is in end to end testing, but selenium or cypress are good for browser based applications.

6. Capture documentation. This might be a higher priority, depending on what your relationship with the existing team is. Few teams will say no to someone helping out with doc. Document high level architecture, deployment processes, key APIs, interfaces, data stores, and more. Capture this in google docs or a wiki if you don’t have an existing solution.

7. Start using data migrations. Having some way to automatically roll database changes forward and back is a huge help for moving faster.

None of these are about changing the code (except maybe the last one), but they all wrap the code in a blanket of safety.

After implementing one or more of these, the team should be able to move faster and with more confidence. This will build trust and allow you to suggest bigger changes, such as bringing in a framework or building abstraction layers.