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SERVICE 02
Legacy System Modernization
Modernization — Legacy System Renewal
Turn "the limits of maintenance" into a renewal plan.
For legacy systems over a decade old, the same team carries current-state assessment, migration design, and parallel operation through to completion. It starts with a design that modernizes without stopping your business.
Process
01
Current-state assessment & tech-debt inventory
02
Renewal policy & migration strategy design
03
Parallel operation & migration implementation
04
Production cutover & operations handover
If this sounds like you
Break out of the "it runs, but we can't touch it any further" state
PAIN 01
A system over a decade old, with rising maintenance costs and frequent errors
Heavy reliance on the incumbent vendor means changes now take more time and money. You can't even keep up with security patches.
PAIN 02
You're worried about your vendor's aging staff and the risk they go out of business
PAIN 03
You're considering cloud migration or modernization, but don't know where to start
You can reach out even if you're just sensing that the current setup is nearing its limit.
Let's talk it through first →
The SYSTEMI approach
Modernize without stopping the business
Replace it or migrate in stages — we present the options in light of your business constraints and technical debt, with parallel-operation design as the top priority.
01
Current-state assessment & tech-debt inventory
Source-code analysis, documentation cleanup, and visualization of the system architecture. We line up the material you need to decide which existing assets to keep and which to discard.
Output
Current architecture diagram / Tech-debt list / Dependency map / Risk assessment
Output
Migration-strategy comparison table / Migration roadmap / Cost estimate / Risk-response plan
02
Renewal policy & migration strategy design
We compare the options — replace, phased migration, or refactor — and present multiple proposals that account for business risk, cost, and timeline.
03
Parallel operation & migration implementation
Using patterns such as Strangler Fig, we migrate to the new system feature by feature. During the parallel-operation period, routing handles the switchover so the service never stops.
Output
Parallel-operation foundation / Data-migration scripts / Cutover plan / Rollback procedures
Output / What happens next
Operations documentation / SRE setup / Monitoring dashboard / Legacy decommissioning plan
04
Production cutover & operations handover
We handle post-cutover monitoring, incident response, and handing things over to the team. Rather than "ship it and walk away," we stay with you until your team can run it on its own.
How we're different
Can they design the "parallel operation" during the renewal too?
What sets us apart is that the same team can see current-state assessment, migration design, and parallel operation through with a single, end-to-end view.
| Large SIer | Freelancer | Small SI firm | SYSTEMI | |
|---|---|---|---|---|
| Depth of current-state assessment | Yes | △ Depends on experience | △ | Yes — cross-cutting assessment by a team of engineers |
| Objectivity of technology selection | △ Swayed by the existing setup | — | △ | Yes — vendor-neutral |
| Parallel-operation design | Yes | Depends on the team | △ Depends on resources | Yes — parallel operation with a dedicated team |
| Consistency from upstream to implementation | △ Lots of handoffs | Yes | Yes | Yes — carried through by the same team |
AI × legacy system modernization
AI makes "code you couldn't touch" touchable again
Legacy code analysis
Claude Code reads through the dependencies in COBOL, old PHP, and Java, and rapidly outputs refactoring candidates and impact scope. That lets people focus on judging "where to start."
Regenerating specifications
For existing systems with no documentation left, we regenerate specifications by combining code comprehension with business interviews. This lines up the assumptions for the new system's requirements.
Automated test generation
We auto-generate regression tests from existing behavior and verify output differences before production cutover. "Nothing is broken" gets confirmed mechanically.
Related cases
Where we deliver the most value
We've included a mix of publishable cases and model cases.
Cleared 250 tickets in one year on an existing system carrying "3 years of backlog"
Challenge
A ticket-management system with an outdated design. A shortage of engineering resources had stalled any improvements.
Outcome
Renewed feature by feature while running in parallel, more than doubling development speed.
MODEL CASE
FDE in action
On a core-renewal project driven mostly by AI hopes, we rebuilt it from the migration strategy and parallel-operation design up
Where the inquiry started
"We want to bring in AI" and "we want to overhaul the core system" were tangled together, the key questions never settled, and it had stalled.
What we framed
Inventory of current assets → comparison of three migration strategies → phased-migration design with Strangler Fig, all framed on the front line.
See all cases →
DELIVERABLES
A sense of what we produce on the front line
Examples of how we structure the actual documents we hand over. We organize them as decision-ready material the next phase can use as-is.
DOCUMENT 01 — Legacy diagnostic report (current architecture, tech debt, migration priorities)
Modernization_Assessment_v1.0.xlsx
Current architectureAn inventory of language, framework, DB, OS, and middleware versions and their support end-of-life dates
Tech-debt listSeverity, remediation cost, and when each item should be addressed
Dependency mapIdentifying integration points such as external systems, batch jobs, and report output
Migration-strategy optionsComparison and trade-offs of replace / phased migration / refactor
Migration roadmapPhases, timeline, team, cost, and risks laid out
DOCUMENT 02 — Architecture proposal diagram
Migration steps — Legacy → Bridge → Modern
Legacy
📦
On-prem / VMwarePhysical or virtual
MySQL 5.7Past EOL
PHP / CakePHPUnpatchedRouting
CloudFront / ALBPer-feature routing
DMS / GlueDB replication / ETL
EventBridgeEvent integrationFrontend
Next.jsTypeScriptAPI / Runtime
ECS FargateRails / Hono
LambdaBatch / asyncData
Aurora v2PostgreSQL-compatible
S3Existing assets + assetsDevOps
GitHub ActionsCI/CD
TerraformIaC
CloudWatchMonitoring / alerts* Migrate to the Modern side feature by feature (Strangler Fig). The Bridge layer routes between both systems, so switchover is possible with no service downtime.
* Once migrated, the Legacy system is monitoring-only → decommissioned in turn.
* Once migrated, the Legacy system is monitoring-only → decommissioned in turn.
Frequently asked questions
Common questions about legacy system modernization
Can you migrate without taking the running system offline?
We adopt phased migration (the Strangler Fig pattern) and switch over feature by feature, in sequence. We support a design that brings downtime as close to zero as possible.
We can't judge how much of this should be replaced on our own.
We start with an assessment that visualizes your current system's dependencies, technical debt, and business impact. We decide together — including whether it's a "full overhaul" or a "phased renewal" — against your business requirements.
Do we absolutely have to move to microservices?
No, it's not required. Refactoring while staying a monolith is also a valid option. We propose a configuration that won't become over-engineered, taking into account your organization's size, deployment frequency, and team structure.
How do you ensure quality after migration?
We combine automated regression testing, canary releases, and phased rollout with feature flags. We also put in place a mechanism that automatically verifies output differences against the old system before production cutover.
Related services
FDE · Forward Deployed Engineering →
SRE & Infrastructure Automation →
Cloud-Native Development →
Tell us about your legacy system challenges first.
Tell us where things stand today, and we'll propose options for a renewal approach.
We can start together from the material you need to decide "whether to renew at all."
Talk to us about legacy system modernization (free)