Varjo Software

My name is Hannu Varjoranta. I am an expert on databases and scalability, launching services on the cloud, and helping hard software projects to achieve their goals.

What is VarjoSoftware?

Varjo Software is a trade name for my one-person freelancing business. My name is Hannu Varjoranta and I focus on building simple, easy-to-maintain, and highly scalable solutions to meet the needs of my clients.

I have more than ten years of experience working with large scale systems, with multiple different high profile companies, like F-Secure in Finland, and Spotify in Sweden. I am currently working as a full-time data infrastructure engineer at Spotify in Stockholm. I have a Master's degree in Computer Science from Helsinki University of Technology (renamed to Aalto University).

System Design

I focus on finding the simplest solution possible to satisfy your needs. The design is done together with the client and adjusted as the software grows.


Automation is more than automating a business process. Automated system can be automatically deployed, scaled based on the load, with minimal maintenance load.


I have experience from smaller relational databases up to widely distributed horizontally scalable systems processing and storing data for over 100 M monthly active users.

Running in the Cloud

You don't need to own hardware to run your business. I have long history of using cloud based hosting services for running larger – and smaller – systems in the cloud.

Open and Pragmatic

I have open and direct personality. I listen and observe your needs, before jumping into conclusions. Best outcomes are based on hard work and trust.

Consulting and Training

Whether you need help on building or designing your system, or leading your next project, I am are here for you. I can also conduct training on subjects related to software, scalability, and databases.


Open Sourced Projects

Cassandra Reaper

Cassandra Reaper is a centralized, stateful, and highly configurable tool for running Cassandra repairs for multi-site clusters.

Cassandra Reaper was created for managing and scheduling anti-entropy repairs for the hundreds of Cassandra clusters maintained at Spotify. As the amount of separate Cassandra clusters was increasing, keeping the clusters in shape with automated repairs was becoming a priority. Main benefits of using Reaper come from automated scheduling of repairs, which get carried out in effective and safe manner. If there are other heavy operations on-going, like compactions or data streaming due node joins, token moves, or similar; Reaper detects these and waits until the particular node is free to continue with repairs.

  • Related System: Apache Cassandra
  • Used Technologies: Java, Python, Cassandra JMX, Dropwizard, PostgreSQL

PostgreSQL Metrics

Postgresql-metrics is a service to extract and provide metrics on your PostgreSQL database.

The existing Postgres monitoring systems did not quite fulfill the Spotify requirements, and this project was built on the idea of minimalism and extendability. Metrics format is standard Metrics 2.0 based, while being fully compatible with Spotify monitoring infrastructure, and easy to integrate into other environments as well.

  • Related System: PostgreSQL
  • Used Technologies: Python, FFWD, Metrics 2.0, JSON


Exconf is a configuration tool for multi-environment micro-service setups.

Exconf provides a structured way to setup your configuration for multi-environment setups containing services, or other configurable systems, that have common configuration structure but different environment specific configuration details. At Magine it is used to have a common single location for all environment specific configuration, independent of the used deployment method, whether it is Mesos/Aurora scheduler or Kubernetes cluster.

  • Related System: Configuration Management
  • Used Technologies: Python, YAML


Spydra is "Hadoop Cluster as a Service" implemented as a library utilizing Google Cloud Dataproc and Google Cloud Storage.

The intention of Spydra is to enable the use of ephemeral Hadoop clusters while hiding the complexity of cluster lifecycle management and keeping troubleshooting simple. Spydra is designed to be integrated as a hadoop jar replacement.

  • Related System: Hadoop, Google Cloud Platform (GCP), Dataproc
  • Used Technologies: Java, YAML


Feel free to get in touch if you have any questions or suggestions.

Interested in hearing more about me?

I tweet about #software, #scalability, and #database related content at @hvarjoranta

If you like what I do, you can follow me on twitter and I will keep you informed about the projects I am working in.

Availability: I am currently working full time, but I do spend about 5-15 hours per week on my own and open source projects. If you need shorter term development guidance or help, you can always ping me for short term availability.

Hannu Varjoranta
Software Architect

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