Advantages of working on a legacy application

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Advantages of working on a legacy application

Are there any advantages of working on such an application? Would you rather prefer working on a greenfield? Here is my stance on this topic and my personal story.

My first (legacy) Rails job

When I finished my Master’s thesis about Ruby on Rails, I had one dream. To work with Ruby on Rails on daily basis. I have already quit my first job in a corporation a few months earlier to focus on studies. I was free to start any job, anywhere. I couldn’t find Rails job at my current city, at that times Rails was not really that much popular in Poland. But I found a new job in Warsaw and moved there. My first Rails job. How exciting.

On my first day I sit down, pulled the repository, installed dependencies and run the tests. Almost everything failing. I looked at the code and it was terrible. So much business logic in controllers and views. I wanted to cry. My contract obligated me to work there for 12 months and I wanted to run away on day one.

My dreams were crashed. I read so many blogposts, articles and books about Rails, about testing in Rails, doing TDD. I wanted to work in Rails because I wanted to work with codebase covered by tests. Just like Ruby is, just like Rails is. But the reality was radically different. Big codebase (>100 models and controllers). Complicated business domain. And useless, failing, obsolete tests which didn’t give you much confidence in refactoring.

You might think that after such experience my answer to the question, I asked at the beginning would be very negative. But on the contrary. I’ve learnt a lot since that time.

The advantages of working on a legacy app

Humble programmer

Legacy codebase teaches you humility. We, the programmers are writing this code. We, our colleages, our friends. Not some mythical creatures from Wonderland. We, ourselves. Doing our best, one commit at a time. And when we look later at our codebase we are often not so happy about the final result. And we need to live with it. Understand our limitations. Keep reading, keep getting inspired, keep getting better.

Long term effects

2 years later I was working in a different place and a developer called me, trying to convince me to move to a new job. It was a marketing agency using Ruby on Rails for websites for their customers. One of his argument when he was trying to convince me was that their projects have an average lifespan of 3 months. So if you make a bad decision regarding architecture or gems or you wrote a bad code, you don’t have to live very long with it. Soon, you will have a new chance to start a fresh project. A new greenfield. I rejected that offer. Legacy applications that you keep working on for years and maintain them give you the ability to understand the long term effects of your decision. You have to live with the consequences. You see which decisions were good and which were bad. What helps you one year later and what you regret. Short them project, new projects usually don’t give you that kind of feedback.

From a few years old, big, inherited Rails app you will learn a lot. What it means to couple every part of the application with every other part of it without any kind of separation. On top of that, coupling with every gem that hook directly into Active Record. After week (months, or even a year - depending on the state of code you inherited) that you spent fighting with small and medium bugs happening everywhere (because of the coupling) you will probably have a much better understanding of the domain of the business. I am working in a project where I can easily name 20 different modules that this application should consist of. Now, whenever a new feature is introduced I am careful to think how it affects all the already existing features. In other words, you learn how the decision you make and others made before you play in the long term.

As my client once said to me: The only reward that we get for being successful (as a business) is more complexity. The bigger the organization, the more processes, features and use cases, the more complexity needs to be handled by the code. That is our curse (because we try to fight the complexity everywhere and there is always accidental complexity added as well) and our reward. Because the feeling that you can handle all that complexity for your client and keep things working and profitable is nice.

Grown businesses and applications give you a tremendous opportunity to recognize bounded contexts in the app. What modules it is built from. Even if you don’t see it on the code level, you start to see it on the organizational level. On the conceptual level. This starts to give you clarity in terms of which way the application should be refactored into.

Keep calm and commit

It’s true that there can be a lot of bad emotions, negativity, frustration, even rage when you work with legacy codebase. It’s interesting that codebase (non living thing, not even a material object) can have such an impact on our feelings. But you can treat it as a lesson. How to convert those emotions into something positive? But to do that you need to have refactoring and communication skills. And desire to keep improving. It’s hard, it’s tiresome and exhausting. But what other options do we have? To give up?

It’s not that you are alone with those problems and challenges. Small companies write shitty code and big companies write spaghetti code as well. In the world where almost everything, from factories, power plants, planes and cars are controlled by software this problem is only going to get bigger. And we need to take responsibility for our actions .

Value driven negotiations

Working on a legacy application makes it easier to operate on value when negotiating with business. Recently I’ve been implementing a cross-selling option for one of our clients. From the frontend perspective it was one checkbox here and a couple of text inputs later. Backend required more work, much more changes, API integration, etc etc. 10 minutes after enabling it with a feature toggle the first customer already purchased this option. We knew it is working, valuable for people and they will keep using. One day later we more-or-less knew the conversion rate. Multiply it by their number of daily transactions, take average value of order into consideration and you have a pretty good guess as to how much money this brings to the table in the next year. Next time when you negotiate your salary or your rate you can use those numbers. Yes, we cost you $X but the features we do for you give you $Z.

When you work on new projects you usually don’t have such a comfort. There is not much traffic, not so many customers and the startup might be still burning money. In such case it is much harder to use the value that you bring to the customer as a starting point for a salary negotiation.

Bigger, older, legacy business are already verified in some way. Either they are at least very good at convincing investors or they are onto something and they are doing something good for the customers. Otherwise, why would they keep coming?

Also, we found that it is much easier to handle billing with such mature organizations. They don’t whine about every dollar they need to pay you. They just pay. In fact, they often want even more of our developers later. They can afford us.


And a final thing that I love most about it. Super fast customer feedback loop. The cross-selling feature for the platform that I told you about, it took 2 weeks and dozens of pull requests and deploys. It was used by an user within 10 minutes. Then I was working on another feature. I was sceptical that people will buy it, but the business product owner wanted to go for it. We did our best, shipped it, enabled on production. Same story. 10 days later and we already knew that it was a success. The fact that you can just ship something and get an immediate feedback is a tremendous benefit.


  • Your legacy project is probably successful if it is capable of living that long
  • The domain is probably quite big and interesting
  • The customers can quickly provide a feedback and let you a/b test the solutions
  • The company behind the project needs you and should pay without problems

I wish you good luck in your legacy project and lot of learning opportunities.

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