Blueprint Before Build: Planning a Server-Side GTM Migration

Marketing Academy · Field Work●Analytics & Attribution

MiniBuild the Asset· 25 minutes

Nubank (Nu Holdings)

Objective: Given Nubank's current client-side-only GTM setup and a list of ad platforms in use, produce a one-page migration blueprint (subdomain, tag priority order, deduplication scheme) before any engineering work starts.

Nubank's growth team wants to move to server-side tracking after Google Ads reported 25% more sign-ups than GA4 last quarter. Engineering has one sprint allocated and needs a spec, not a vague request to 'set up server-side tracking.'

Sequence the plan the way the lesson does: subdomain first, then server tags in priority order, then the deduplication scheme, since building tags before the subdomain exists wastes the sprint.

Before you start

What you'll need

Free path (everything below is enough to finish)

Google Sheets

FreeDraft and share the migration blueprint with engineering

Free, fast, and every engineer can comment directly on the spec

The process

2 steps

Step 01 of 02

First-party subdomain setup

The lesson is explicit: a tagging server must live on a first-party subdomain like metrics.yourbrand.com. A vendor domain like gtm.stape.io is still third-party to the browser and still gets blocked.

Nubank's DevOps team proposes hosting the server at nubank-tags.stape.io to save setup time. Does this achieve the goal?

Google Sheets— Draft the migration spec document, one row per decision.

Procedure

Open a new sheet titled 'sGTM Migration Blueprint'
Row 1: propose the subdomain (e.g. metrics.nubank.com.br) and the CNAME target
Row 2: note explicitly why a vendor-hosted domain (e.g. stape.io) fails the first-party requirement

Sample output

Decision: Subdomain
Proposed: metrics.nubank.com.br -> CNAME -> [sGTM host]
Rejected option: nubank-tags.stape.io
Reason for rejection: still resolves as third-party to the browser, ad blockers and ITP treat it identically to the current setup

Healthy

The blueprint names a first-party subdomain on Nubank's own domain and explicitly rules out the vendor-domain shortcut with a reason.

Unhealthy

The blueprint accepts the vendor-hosted subdomain to save a week of DNS work, which ships a migration that doesn't actually bypass ad blockers.

What this means

The subdomain choice is not a convenience decision, it is the one step that determines whether the whole migration achieves anything.

So what do I do about it?

Symptom	Action	Effort
A vendor-hosted domain is proposed to save setup time	Reject it in the spec and require a CNAME onto the company's own domain before engineering starts	5 min

YouYou can do this yourself, no engineering access required.

Step 02 of 02

Sequencing server tags by ad-spend priority

The lesson's Step 4 says to add server tags for every destination, but a one-sprint migration can't build all of them simultaneously; the setup work is real engineering time per platform.

Nubank runs Google Ads (54% of paid budget), Meta (31%), and LinkedIn (15%). Engineering has time to build and validate 2 of the 3 server tags this sprint. Which 2 go first?

Google Sheets— Add a 'Tag Priority' row to the same blueprint sheet.

Procedure

List each ad platform with its share of paid budget
Sort descending by budget share
Mark the top 2 as 'Sprint 1' and the remainder as 'Sprint 2'

Sample output

Platform      Budget Share   Sprint
Google Ads    54%            1
Meta CAPI     31%            1
LinkedIn CAPI 15%            2

Healthy

The two highest-budget platforms ship first, so the sprint's ROI is front-loaded onto the campaigns where the data gap costs the most money.

Unhealthy

Tags are built in whatever order engineering finds easiest, which might ship LinkedIn CAPI first while 85% of the budget still runs on unfixed tracking.

What this means

When you can't build everything in one sprint, sequence by where the money is, not by implementation difficulty.

So what do I do about it?

Symptom	Action	Effort
Engineering has capacity for 2 of 3 platform integrations this sprint	Build server tags for the top 2 platforms by budget share first	half day

EitherYou or a developer can handle this, depending on your access.

Final deliverable

A one-page sGTM migration blueprint: proposed subdomain and CNAME target, sprint-1 vs sprint-2 tag priority by budget share, and the event_id field to use for deduplication.

See a reference example

Sample output

Coinbase, sGTM Migration Blueprint (excerpt)

Subdomain: metrics.coinbase.com -> CNAME -> sGTM host
Sprint 1 tags: Google Ads (62% of budget), Meta CAPI (28% of budget)
Sprint 2 tags: TikTok CAPI (10% of budget)
Deduplication field: transaction_id, shared between browser pixel and server tag

Success criteria

You're done when you can:

Rejects any vendor-hosted subdomain shortcut with a stated reason
Sequences tag-building priority by ad-spend share, not by build convenience
Names a concrete deduplication field for the chosen conversion event