01
Context & Problem Statement
The PADI web modernization effort needs to proceed in parallel with the ongoing Platform Engineering (PE) stream on the existing live website. Today both would share a single Acquia Cloud application, which means shared environments and deployment pipelines — any modernization work risks destabilizing the live PE build, and there is no clean isolation between the two streams.
To do this, we need three things:
- Additional environments and genuine isolation, so modernization work cannot affect ongoing PE delivery
- Independent deployment pipelines that don't step on the current build site
- A path to zero-downtime production cutover
Acquia Cloud does not support a zero-downtime cutover within a single application, so the only way to move from the existing site to the new one without downtime is a DNS cutover from one app to another.
A separate application also accommodates the planned front-end hosting, which should not be coupled to the existing application. Front-end hosting will be covered in its own ADR once pricing is confirmed.
How do we run modernization in parallel with the PE stream without affecting it, and cut over to the new site with zero downtime?
02
Decision Drivers
- Isolation of modernization work from the live PE stream — no shared environments
- Independent deployment pipelines that don't disrupt the current build site
- Zero-downtime production cutover, which Acquia Cloud cannot do within a single application
- Decoupling of planned front-end hosting from the existing application
03
Considered Options
Considered
Option A
Single app, separate environments
Provision additional environments within the existing Acquia Cloud application for modernization work.
Considered
Option B
Single app, Git branch isolation
Keep one application and pipeline, isolating modernization via branching and feature flags.
Chosen
Option C
Second Acquia Cloud application
Full application-level isolation, with a DNS cutover from the existing app to the new one.
04
Decision Outcome
Chosen — Option C
Second Acquia Cloud application, because it is the only option that delivers true environment and pipeline isolation from the live PE stream while enabling a zero-downtime DNS cutover — neither achievable within a single Acquia Cloud application.
05
Consequences
- GoodModernization proceeds with full isolation — no risk to the live PE build.
- GoodThe two streams run on independent deployment pipelines and can't step on each other.
- GoodEnables a zero-downtime production cutover via DNS between applications.
- GoodPlanned front-end hosting can be attached without coupling it to the existing application.
- BadIncurs additional Acquia Cloud cost for a second application.
- NeutralThe two applications are owned by two separate teams with no overlap, so operational overhead does not compete for the same people.
- NeutralNo content is created on the new environment during development, so there is no content-divergence or sync risk before cutover.
06
Confirmation
The second Acquia Cloud application is provisioned with its own environments and deployment pipelines, validated by a successful isolated build and a rehearsed DNS cutover in a non-production environment.
07
More Information
Front-end hosting for the new application will be addressed in a separate ADR, pending pricing confirmation.