A large application estate migrated and brought under Azure DevOps

The challenge

Arc Infrastructure operates Western Australia's south west rail network, about 5,500 km of rail infrastructure. Its technology group engaged Interfuze to migrate its internally developed applications to new SQL Server and application server instances, and to use the migration to set up governance and agility through Azure DevOps, decommission unused applications, and create high-level test plans and consistent documentation for every application.

The scale was large: over 120 internally developed applications in Arc's applications register, whose entries were not always correct. The applications depended on one another, several versions of the code existed, and the version in production was not always documented. They were written in .NET, VBA and Access, as desktop, web and standalone executables, and the desktop applications needed installers that did not exist.

There were legacy issues too. Test plans did not exist, functionality was not always clear, the original authors had left Arc, and configuration was hard-coded.

Our approach

We identified every application that might depend on the existing SQL Server and application server, from the applications register and all the known code, and mapped the interdependencies between applications to define the cutover plans. The migration process was designed to minimise risk while balancing it against the time spent.

Each application got an Azure DevOps pipeline with automated builds and deployments. We cleaned the code to remove hard-coded configuration, so each application can deploy to several environments. The migration ran in three steps to reduce risk: first the current code, so a known version was in production; then the cleaned code; then the move to the new SQL Server.

Detailed run plans and design and tooling improvements for the interdependent applications kept the cutovers clean. The largest deployed 31 applications at once.

The outcome

The migration to the new SQL Server and application server instances was seamless, and every application now runs in a high-availability environment.

All 57 migrated applications are in Azure DevOps, with one-click deployments and high-level test plans. The applications register is up to date, and all the code in production is known. Of the 120 applications reviewed, 21 were decommissioned, and 185 change requests and 192 deployments were executed.