Backend Software Engineer (various levels) - ad serving & analytics

Ljubljana, Slovenia | Product Development | Full-time | Fully remote


About Celtra

At Celtra, we are building two world-class products. The first product (Creative Enablement or CE) has already been a growing market leader for a couple of years now, helping companies such as CNN, TripAdvisor, Bloomberg, NBCU, and Business Insider monetize their advertising inventory. It covers the entire lifecycle of launching a campaign: ad product ideation and design, ad content production, trafficking tags, and tracking performance. With our second, younger product (Creative Automation or CA), we are chasing a much bigger opportunity by helping brands produce a massive amount of content better, faster, and more efficiently. Although its development is still in the early days, it already includes an impressive list of customers such as Spotify, adidas, Shopify, Unilever, P&G, LEGO, Lululemon, and many others. 


Who are we searching for? 

We are looking for a Backend Engineer to join the Creative enablement team (CE) and will help us build, maintain and improve different parts of the Celtra platform. Your work would mainly impact various backend services built around ad serving and analytics infrastructure. 


What would be your responsibilities? 

  • building critical fault-tolerant services that are always on,
  • processing ad request in real-time (< 20 milliseconds),
  • processing events for ad personalization using real-time streaming infrastructure,
  • handling a large volume of user’s data,
  • using distributed mechanisms to parse large amounts of data and insert it into data warehouse


What are the challenges ahead?

Our team’s future challenges include:

  • envisioning and implementing new product usage analytics for the whole platform
  • building tool for traffick replay that will enable us faster migrations to new technologies and stacks
  • checking our current analytics pipeline and proposing improvements e.g., use sharding before Spark


What kind of tech stack do we use?

On the Creative Enablement product you will be able to learn Scala, NodeJS, PHP, MySQL, Spark, Snowflake, and you will also find Go, MongoDb, Dynamo and Kinesis. Everything runs on the AWS cloud, and the Kubernetes cluster orchestrates it. 

What are our expectations?

You care about clean code. You write high-quality, maintainable code and are aware of industry best practices and trends. You proactively identify possible technical issues  before it turns into long-term problems,  and you encourage others to do the same. We always do code reviews to provide feedback and ensure code quality.


You have strong  troubleshooting skills. You are not afraid to parse logs, look at machine metrics or go deep into the code to understand what went wrong. You do not jump to conclusions, but act based on facts and evidence. 


You’re dedicated to dig deep. You also don't stop at the first solution, but are willing to go beyond and check the source code of frameworks and understand them as you know that a small change can make a huge difference in the end.


You’re a  team player. You work well in the team, are willing to share the knowledge, and want to help others as you know only a strong team can succeed.



  • Good understanding of at least one programming language (preferably statically typed).
  • Understanding of various software paradigms and architecture styles (REST, OOP, MVC, etc).
  • Basic knowledge of algorithms and data structures
  • Experience with relational databases
  • Experience with different automated tests approaches and knowledge of when to apply them


We appreciate:

  • Experience with AWS or another cloud computing platform.
  • Experience with Scala or Java.
  • Experience with Go 


What do we offer?  

In Celtra it’s all about looking beyond the surface, beyond the numbers, and really trying to see the qualities that are at the core of each person, their talents; the discovered ones or better still, the undiscovered ones. We look for people who naturally want to take responsibility for their own success, and strive to do something that has a tangible impact. To our best talent, we give them the freedom to do the unusual. 


Compensation depends on experience and knowledge, but here’s what we offer in general:

  • A competitive benefits and compensation package 
  • We place great importance on the professional development of our employees 
  • Comprehensive health coverage and additional pension insurance 
  • We provide plenty of opportunities for employees to seek a more active and healthy lifestyle. We provide a dedicated budget for any kind of sport activities employees are passionate about, and we sponsor group sports activities such as basketball and yoga lessons. 
  • We provide employees with top-notch working equipment and an additional budget for your home office.