Feasible through the Workflow Engine's rolling drain, but real preparation is needed: dual-version discipline, better tests, or schema care before at-will release is sensible. Legacy runtime: the rolling drain works (stealth releases prove it) but relies on fix-forward risk rather than dual-version safety.

• 1 system(s) depend on this repo; during a rolling deploy they will talk to old and new versions at once, so responses must stay compatible
• Consumes WCF contract packages: never take a breaking client bump mid-feature, and treat obsolete warnings as migration debt

1. Adopt the four-stage discipline from the ZDD engineering standard: pre-deployment compatibility, deployment, feature activation behind a flag, post-release cleanup.
2. Raise automated test coverage first: ZDD trades the end-of-sprint manual gate for continuous automated confidence, so the tests are the entry ticket.
3. Make every change dual-version safe: backwards-compatible APIs (new major version for breaking wire changes), expand and contract for any schema change, and consumers tolerant of unknown fields.
4. Audit serialized data: anything in Redis, queues or shared caches must deserialize cleanly across adjacent versions.
5. Wrap behaviour changes in feature flags so code deploys dark and release becomes a business decision, not a deployment event.
6. Route deployments through the Workflow Engine's automated drain, deploy, health-check, return cycle (the path proven by the first automated production run in mid-2026).
7. Verify with area-scoped regression rather than the whole-platform cycle, and watch error rates after rollout with automated rollback on alert.

sqlserver:TCDB, sqlserver:TravelCounsellors are shared, so this system cannot change engine on its own: every sharer moves in convoy. Either agree the move with all sharers as one programme, or first split this system's data out behind an owned API, then follow the steps below.

• sqlserver:TCDB is shared with 1 other system(s)
• sqlserver:TravelCounsellors is shared with 4 other system(s)

1. Inventory the schema and query surface of sqlserver:TCDB, sqlserver:TravelCounsellors: tables, stored procedures, triggers, cross-database joins and anything else engine-specific.
2. Confirm the target: PostgreSQL (relational model; keep transactions and joins, swap the engine).
3. Replatform to modern .NET first (see the recommended actions): current PostgreSQL and MongoDB drivers and EF Core providers target modern .NET, and doing one risky change at a time is cheaper than doing two.
4. Data access is not through an ORM, so port the SQL by hand: translate T-SQL constructs, replace stored procedures with application code or target-native equivalents, and add integration tests around the queries that matter first.
5. Stand up the target alongside SQL Server, backfill with an ETL pass (pgloader or an export/import job), then dual-write or replicate until parity is proven.
6. Move reads to the target, watch correctness and latency, then cut writes over and keep SQL Server read-only until confidence is earned.
7. Decommission the SQL Server database and remove the connection strings and firewall paths that pointed at it.

Appropriate, but the .NET Framework runtime has to go first; container work rides along with the replatform rather than preceding it.

• .NET Framework only runs on Windows; practical (Linux) containers need modern .NET

1. Replatform to modern .NET first (see the recommended actions). Containerising then becomes routine.
2. Add a Dockerfile and make the app read all configuration from environment variables and the secrets manager, never from machine-local files.
3. Log to stdout and expose a health check endpoint so ECS can supervise it.
4. Adopt the shared ci.yml pipeline template with the container parameters (awsRegion, containerAfterBuild, ecsTerraformRepo), which is exactly how the estate's existing AWS services deploy.
5. Define the service in the Terraform repo, deploy to a non-production environment, then shift traffic and disarm the deployment-group release pipeline.