Migration on Brian Faust

The Strangler Pattern Still Needs an Exit Plan

Fri, 01 Nov 2019 00:00:00 +0000

A replacement proof of concept imported one provider’s postal data into PostgreSQL and served one existing JSON-RPC search method from a Go binary. A checked-in request and response fixture preserved field names, nulls, empty strings, ordering, and identifier shape. Import failure left the last committed dataset intact.

The slice deliberately excluded every other provider, the other RPC methods, queues, schedulers, authentication, caching, operational interfaces, and traffic cutover.

That is a good proof of one vertical path. It is not a plan for retiring the system around it.

A Rewrite Needs a Behavior Ledger

Wed, 01 May 2019 00:00:00 +0000

A desktop rewrite had screens for shipments, reports, settings, and logs. A feature checklist could have marked those areas complete.

The old application also had behavior no screen list would reveal:

a failed temporary-file cleanup must not turn a submitted print into a failure, or the next run may print the label again;
the first run treats older unprinted records differently from later runs;
setup unlocks when a credential setting exists, not when its value is non-empty; and
a visible report search box does nothing.

Some of those rules protect operators. One is an awkward contract. One is probably a dead feature. A rewrite cannot treat them all as “parity.”

Parallel Implementations Are Not a Replacement Seam

Mon, 01 Apr 2019 00:00:00 +0000

An old shipping integration and its proposed replacement lived beside each other. Both had an interface. Both had a driver, request builders, and tests. That looked like a seam.

When the replacement was finally made canonical, the change still crossed dozens of files. The old interface disappeared, the new one moved, the canonical driver changed its pickup and shipment flows, and a parallel driver tree was deleted. Follow-up work then corrected a request shape and added serialization tests.