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ASOS: How they migrated from local monolith to microservices in Azure

Posted on 21 June, 2017

Director, Microsoft Mechanics

Join Dave Green and the ASOS team, on June 29th at 9am PDT for their AMA session on the Microsoft Tech Community at

Today we are kicking of a new series on Microsoft Mechanics called "How we built it" to share the real-world architectural back stories and best practices as told by the technology architects in our customer organizations.

We kick off the series with lead architect, Dave Green, from British online fashion retailer ASOS, to take a closer look at their design goals and approach for moving from a locally-operated monolith to a fully architected built-for-Cloud online retail system.

Breaking down the monolith

Founded almost two decades ago, ASOS was ahead of its time establishing a fully-online retail presence. The company has a growing customer base of 14 million customers, spanning 230 countries worldwide. Their exponential growth resulted in the need to move beyond a single currency and support multiple languages.

This meant building in more agility, scale and efficiency into their tech architecture. Rather than perform a lift and shift migration, the team decided to adopt a cloud-native, microservices architecture from scratch for faster iteration and release of new features.

Then they set to work breaking down their monolithic retail app which comprised stateful, intertwined services into core microservices, swapping out functions from the monolith piece-by-piece.


As Dave Green explains, core to their approach was the decoupling of their presentation layer from their compute layer. This gave them more freedom to easily add or change features and scale their developer teams to work on multiple features at once. Further, as each service maintains its own state and data, this made it easier to scale the data layer and compute layer independently.


Multi-geo footprint and performance

Breaking down the monolith and moving core services to the Cloud also enabled them to architect for greater performance and resiliency for their global customer base. This included geo-redundancy across North and West EU regions, where most of their customers reside with a handful of core services sensitive to latency, running in Asian and North American regions.


The combined approach with Cloud microservices, paid off on some of their busiest shopping days. This includes Black Friday, where they saw an increase in peak order handling from 9 orders per second using their original monolith retail system to 33 orders per seconds with their Cloud microservices architected system.

To learn more, watch Dave Green's account on "How we built it." You can also join Dave and the ASOS team, on June 29th at 9am PDT for their AMA session on the Microsoft Tech Community at