AWS migration at ImmobilienScout24

Migration with AWS. Problem solutions for: too much work - too little time; new knowledge; tight process and project management

The Project

In order to remain fast, flexible and customer-oriented, ImmobilienScout24 had to migrate all its applications from its previous data center to AWS. The project team chose a Replatform approach to do this. As the contract with the data center was to be terminated at a certain date, the project had the highest priority and required a very tight schedule in order to meet the deadline.

A suitable process was chosen and developed with AWS Professional Services at the end of 2018. About half a year into the migration ImmobilienScout24 sought advice through the AWS Partner Network and contacted us to help them successfully accelerate the completion of the project.

The Problem / The Challenge

There were three major challenges to be tackled during the AWS migration:

  • Tight deadlines: Replatforming required every application in the data center to be touched, and operations were to be impacted as little as possible. The company wanted to parallelize more migrations to finish the entire migration earlier and free up key personnel for other projects.
  • New knowledge necessary: During the migration, some teams had to learn many new technologies, some had to learn how to work in the Cloud and how to incorporate this new way of working into existing processes.
  • Project management: To keep to the schedule, many teams had to migrate their applications simultaneously. Teams had to be assisted with the migration factory process to minimize variation and quickly complete their migrations.

Our contribution

Challenge 1: Tight deadlines:

kreuzwerker helped ImmobilienScout24 migrate many applications. We were integrated into existing teams and provided technical and process support. In some cases, the kreuzwerker team independently migrated applications to parallelize and avoid delays.

In line with the slogan, “We touch running systems”, among other things, we

  • dockerized existing Java (Spring), Scala and php applications, and secured them with Oauth2 , as well as adapting logging and metrics collection
  • rewrote the functionality of a Legacy Scala application in Spring Boot
  • migrated an Elasticsearch cluster from 1.6 to the latest version of AWS

Furthermore, we made changes to the existing data center infrastructure by switching traffic and going live with the applications in the Cloud, following the procedures used by every team.

Challenge 2: New knowledge necessary

In the course of the migration, many AWS solutions such as CloudFormation, ECS and SSM, along with technologies such as Docker, Datadog, OpsGenie and Jenkins were introduced by ImmobilienScout24. Knowledge and experience varied in the teams. Some teams had to expeditiously learn these technologies at a professional level. For daily work with the Cloud, it was also necessary to adapt established processes - especially with regards to deployment and observability. Thanks to our many years of experience with these technologies and processes, we were able to pair and assist the teams, and make ImmobilienScout24 employees even more proficient with Cloud technologies.

Problem 3: Project management

The simultaneous coordination of many teams and the large number of to-be-migrated systems was handled by the excellent project management and processes set up by ImmobilienScout24 and AWS. The kreuzwerker team supported the project management team by taking care of a set of individual teams (on-site and remote) and guiding them through all processes to bring the project to a successful conclusion.


The multitude of applications to be migrated, the tight schedule and the required knowledge made it necessary to engage a strong and reliable partner for the AWS migration at ImmobilienScout24. With intensive onsite support for various applications and teams from the experienced kreuzwerker team, the migration was completed successfully as planned and on time.

ImmobilienScout24 is the leading online marketplace for residential and commercial real estate in Germany. Every month, around 14 million users visit the portal which offers a wide range of services, innovative products and valuable decision-making tools.