She leads tech at a UK lead-gen SaaS. A CodeIgniter 3 codebase from 2019. 95 routes. PHP 7.4, past end-of-life. The original agency was unreachable, and hiring senior PHP for CI3 took 4 months and a 30% salary premium.
Migration CodeIgniter to MERN migration · legacy PHP modernization · UK
CodeIgniter to MERN migration for the team leaving PHP. without losing a user or invoice.
You've decided PHP isn't the long-term answer. We move you off CodeIgniter 2 / 3 / 4 onto Node + Express + React + Mongo or Postgres — surface by surface, never big bang, every flow rebuilt with tests.
4CI → MERN migrations shipped
5-dayfixed-scope audit (£8K)
0double-charges after cutover
Why founders + CTOs migrate now
You don’t need to leave CodeIgniter. You need to leave the version of it that’s costing you growth.
Hiring senior CI3 talent takes months and a salary premium. Your team wants one language across the stack. Node plus React is that clean break, and a legacy PHP modernisation is the moment to add tests.
“We left PHP for good. Hiring time dropped from four months to three weeks, and not a single customer was double-charged through cutover.”
001
4
CodeIgniter to MERN migrations shipped since 2019.
002
PHP 7.4
Past end-of-life version we most often migrate off.
003
42%
Test coverage on the lead-gen SaaS by cutover, from zero.
The founder this page is for95 routes · PHP 7.4 EOL · zero tests
Ananya had a board ultimatum: modernise, or sell the engineering org.
There were zero tests. A failed third-party Stripe migration had left 11 customers double-charged. The team wanted Node plus React. The version of CodeIgniter they were on had become the thing slowing every release down.
Eighteen weeks, strangler-fig. Auth ported first, sessions bridged. Reads next, writes last. Stripe rebuilt with idempotency. CSV import as streamed jobs. Hiring time dropped from 4 months to 3 weeks. This page is for the founder who has decided the migration is happening.
Our CodeIgniter to Node JS migration process
Four phases
No mystery box. Each phase is fixed-scope, fixed-price, and ends with a written deliverable you can show your board. You decide whether to continue at every boundary.
Phase 01
Migration audit, 5 days, £8K fixed
Two seniors read your CodeIgniter estate. Output: a 20 to 30 page audit pack with risk matrix, target architecture, data migration plan, rollback plan, and a fixed quote.
Phase 02
Plan and parallel build, 2-4 weeks
We build the MERN target in parallel. Your CI system keeps running. Data dry-runs, integrations rebuilt, dual-write or shadow-read set up. No customer-facing change yet.
Phase 03
Cutover, 1-3 days, planned window
Often a weekend. We dual-run, shadow-read, then flip the canonical write path. Old system stays read-only for 60 days. Rollback rehearsed and reversible.
Phase 04
Stabilise and decommission, 2-6 weeks
We monitor, fix what only real traffic reveals, hand over, and decommission the old CodeIgniter estate on a schedule you sign off. Nothing deleted until you say so.
The default MERN stack we migrate to. And the substitutions when your team has constraints.
We default to MERN + Python + AWS. We're comfortable on GCP, Azure, Cloudflare, DigitalOcean, Vercel, and Fly.io where your team has a relationship or a reason.
T1
Default target stack
MERNNode.js + ExpressReact + Next.jsTypeScriptMongoDB + MongoosePostgreSQL + PrismaBullMQClerk / Auth0Stripe + idempotencyResendMixpanelJest + PlaywrightTailwind
T2
Migration-specific tooling
on the way throughPHP CLI exportCI3 mysqldumpBull BoardPercy visual parityStripe CLIMongoDB CompassTablePlusPython
T3
Infra, observability, safety net
AWS-defaultAWSRDS / DocumentDBAWS LambdaSQS / EventBridgeS3 + CloudFrontSecrets ManagerRedisTerraformDatadogSentryCloudflarek6 / Artillery
Migration risk + mitigation matrix
Eight risks that sink migrations. How we close each one before cutover
We don’t pretend migrations are safe. We make the risks legible and mitigated, in writing, before a single line of production code changes.
Big-bang vs strangler-fig
Big-bang on an estate older than three years is high risk. We strangler-fig: route by route. Auth first, then reads, then writes. Each surface ships independently.
CI custom auth Clerk / Auth0
Session cookies bridged via a dual-write so logged-in users stay logged in. We then force a password reset to migrate to Bcrypt + Clerk.
MySQL MongoDB or PostgreSQL
MongoDB for flexible-schema customer + product data. PostgreSQL for billing + audit. Often hybrid. We model both at audit and recommend.
CI cron + queue BullMQ / SQS
CI “queues” are usually cron + database polling. We replace with BullMQ + Bull Board with idempotency, or AWS SQS + Lambda for serverless.
Local uploads S3 + signed URLs
CI uploads moved to S3 with presigned URLs and image processing via sharp / Lambda. URLs preserved and redirected, so nothing 404s.
CSV import + batch jobs
Batch jobs are where CI apps explode. We rebuild them as streamed BullMQ jobs with idempotency, audit log, and a dead-letter queue. No more silent failures.
Stripe + idempotency
Old CI Stripe integrations rarely use idempotency keys. We rebuild with idempotency + webhook DLQ + ledger reconciliation. The double-charge risk closes.
Zero coverage to defensible coverage
We add Jest unit and Playwright E2E on critical paths as we port. Target 30-50% by cutover. The cutover itself becomes a test.
Results
CI3 + PHP 7.4 lead-gen SaaS,
CI3 + PHP 7.4 lead-gen SaaS,
to Node + React + Mongo, in numbers
The brief was to leave PHP for good. Eighteen-week strangler-fig migration. Auth via Clerk. Stripe rebuilt with idempotency. CSV import as streamed BullMQ jobs. MongoDB for flexible data, PostgreSQL for billing.
The migration
18 wk
Strangler-fig sprint
95
Routes ported
Runtime + safety
7.422
PHP EOL to Node 22
0
Double-charges post-migration
Coverage + hiring
42%
Test coverage by cutover
4mo3wk
Time to hire
Audit, then sprint. Pricing in the email back.
Pick the shape that fits and Mohit will send your real number inside 24 hours.
5-day migration audit
Two senior engineers read your CodeIgniter estate, data, and integrations. We map the migration and quote the sprint.
- Two seniors, 5 days
- Risk matrix + target architecture
- Data migration + rollback plan
- £8,000 fixed, no commitment to build
MERN migration sprint
Parallel build, dry-run data migration, planned cutover, stabilisation, decommission. 8-16 weeks by estate size.
- Node + React + Mongo / Postgres
- Strangler-fig, surface by surface
- 30-day walk-away both ways
- From £35K fixed (GBP)
Post-migration retainer
One day a week of senior engineer for 3-6 months. New surface area, performance work, integrations, your team unblocked.
- One senior day per week
- Performance + new features
- IP assigns on every commit
- From £5K / month (GBP)
“We left PHP for good. Hiring time dropped from four months to three weeks, and not a single customer was double-charged through cutover.”
— Ananya, Head of Tech, UK lead-gen SaaS
CodeIgniter to MERN migration · honest answers
What founders + CTOs actually ask on the audit call
Direct answers, no marketing varnish. Click each one to open it.
Q(01)
Should we move to Laravel or MERN?
Laravel if your team is staying PHP-fluent and you want maximum framework use. A CodeIgniter to MERN migration if you want one language across the stack and a wider hiring pool. We’ll recommend at audit based on your team, not a preference we brought to the call.
LaravelMERNTeam fitHiring pool
Should we move to Laravel or MERN?
Q(02)
How long does a PHP to MERN migration take?
12 to 20 weeks is typical. CI age, route count, custom library depth, and the auth, payment, and queue surfaces drive scope. The 5-day audit gives you the real number, fixed, before you commit to the sprint.
12-20 weeksFixed quote5-day audit
How long does a PHP to MERN migration take?
Q(03)
Will customers notice the migration?
With the strangler-fig pattern, surfaces flip behind feature flags as they reach parity. Auth migrates with session bridging, so logged-in users stay logged in. Most customers don’t notice. Cutover events are zero-downtime per surface.
Strangler-figFeature flagsZero-downtime
Will customers notice the migration?
Q(04)
MongoDB or PostgreSQL?
Often hybrid: MongoDB for product and customer data, PostgreSQL for billing and audit. We model both at audit and recommend per surface. You’re not locked into one for the whole CodeIgniter to MERN stack migration.
MongoDBPostgreSQLHybrid
MongoDB or PostgreSQL?
Q(05)
Our last agency took the deposit and disappeared. How do we know you won’t?
30-day walk-away both ways, and the audit is fixed at £8K before any build commitment. UK VAT registered, on Companies House, shipping since 2019. You’re never more than the audit fee at risk before you’ve seen a real plan.
30-day walk-away£8K fixed auditSince 2019
How do we know you won’t vanish?
Q(06)
Can we pause if our funding slips?
Yes, with 14 days’ notice. Engineers move to other projects, spend pauses, and you resume with 14 days’ notice. No cancellation fee, no restart fee. The old CI app keeps running the whole time.
14 days noticeNo restart feeOld app live
Can we pause if our funding slips?
In context
Inside the work.
A look at the kind of codeigniter to mern migration surface we hand over — real screens, real data, documented and yours from day one.
Five lines. That's it.
Send your current CodeIgniter estate (traffic, data size, integrations), why you want to migrate, and the deadline you're working to. Mohit replies inside 24 hours with availability and the next 5-day audit slot.
What happens after the email lands
- < 24h
A personal reply.
Availability and the next available 5-day audit slot. Straight to your inbox.
- Week 1
The 5-day audit.
Risk matrix, target architecture, data migration plan, and a fixed migration quote.
- Cutover
Off PHP for good.
Surface by surface, never big bang. Old CI app read-only until you sign off the decommission.