senn-techWinline ERP In-House: Why We Don't Move Core Software to the Cloud
The ERP is the engine room. Every booking, every customer, every invoice runs through it. This data does not belong in a foreign cloud — it belongs on a server whose disks you can physically touch in a pinch.
Why Winline?
Winline is an ERP from the midmarket for the midmarket — no SAP, no Dynamics overcomplexity. It covers financial accounting, inventory management, payroll, CRM, and industry-specific modules and runs with a Microsoft SQL Server as the database backend.
The decisive advantage: The database is open. You can access it directly via SQL, build your own evaluations, write integrations — without having to go through an API layer designed by someone else.
In-House Operation: The Database Belongs to You
Winline on-prem means: SQL Server Express or Standard Edition on a VM in your own Proxmox cluster. The backup runs over the same infrastructure as all other databases — ZFS snapshots, Proxmox Backup Server, offsite sync to Hetzner Storage Box.
No cloud provider has access. No SaaS provider can cut off access. No monthly per-user fees.
Integrations: What We Have Connected
- MCP Server: Read access for coding agents — customer master, open items, articles — so generated code is based on real structures
- Metabase: Dashboards directly on the Winline data — revenue by region, open invoices, inventory turnover
- n8n: Workflows for invoice intake, status messages to customers, escalation for overdue items
- Paperwork Integration: PDF incoming invoices via OCR into financial accounting — plus a dedicated article
Customization: The Underestimated Strength
The Winline data model is documented. Custom fields, custom tables, stored procedures — all possible without the vendor needing to be involved. Where other ERPs require an expensive customization loop with the vendor, Winline often just needs an SQL script and a button in the form.
The Limits
Winline is no beauty contest winner. The interface is functional, not modern. The licensing model is not open source. And: It runs on Windows — SQL Server on Linux or not, the Winline client and middleware want Windows.
Conclusion
An ERP on-prem is not a step backward, but a commitment to sovereignty over your own core data. Winline delivers the open data model and SQL basis for this, without the complexity of the large systems. For the midmarket, this is exactly right.
Why not just move the ERP to the cloud?+
The ERP holds the most sensitive data — every booking, every customer, every invoice. On-prem means: no cloud provider has access, no SaaS provider can cut off access, no monthly per-user fees. The database runs as SQL Server on a VM in your own Proxmox cluster, backed up via ZFS snapshots, Proxmox Backup Server, and offsite sync to a Hetzner Storage Box.
How can Winline be connected to other systems?+
The decisive advantage is the open database: you access it directly via SQL, without going through someone else's API layer. We've connected an MCP server (read access for coding agents), Metabase dashboards, and n8n workflows, among others. The documented data model allows custom fields, tables, and stored procedures — often an SQL script beats an expensive vendor customization loop.
What downsides does Winline on-prem bring?+
Winline is no beauty contest winner: the interface is functional, not modern, and the licensing model is not open source. It's also Windows-bound — SQL Server would run on Linux, but the Winline client and middleware want Windows. Accept that, and you get an open data model without the complexity of the large systems.