About Rens Vermeulen

I'm Rens Vermeulen, an infrastructure engineer specialising in Citrix NetScaler, the platform you may still know as Citrix ADC or NetScaler ADC. I write about what happens when you run NetScaler appliances in production; GSLB, content switching, NetScaler Gateway, and the troubleshooting sessions that took far longer than they should have.

Alongside the deep technical work, what I enjoy most is taking a complex problem and explaining it at the right level for whoever needs to understand it, whether that's another engineer, a security officer or a project manager.

Everything here is written down so the next engineer hitting the same problem finds an answer instead of a dead forum thread.

rens.vermeulen@gmail.com

Career

2024 – Present

NetScaler & Infrastructure Specialist

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Lead responsible for professionalising, securing and future-proofing the entire NetScaler estate across both IT and OT. I shape architecture decisions, automate load-balancing delivery with Ansible and CI/CD pipelines, and produced the full technical documentation set (HLD, LLD, logical and technical designs). Built a new GSLB infrastructure for availability and failover, delivered OAuth API (401-based) authentication, documented Kerberos Constrained Delegation, extended logging to Splunk and monitoring to Zabbix, and ran a Web Application Firewall proof of concept toward production.

2022 – 2024

Technical IT Consultant

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Delivered implementation, optimisation and migration projects across customer infrastructures: Citrix NetScaler configurations, firewall and Intune workplace setups, Azure landing zones, and complete on-premises-to-cloud migrations. Wrote detailed technical designs (current/target state, logical, technical and physical design, migration plan), implemented an Always-On VPN solution and resolved complex network problems under tight deadlines.

2020 – 2022

Connectivity Specialist

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Owned secure inbound connectivity for the data centre via Citrix ADC (NetScaler), managing a platform of 30+ ADCs — MPX 8000, SDX 14500 and 15000 series, and VPX. Implemented load-balancing and reverse-proxy building blocks, PKI-based encryption for RPX and LB services, and complex policies to protect web applications. Automated operational tasks through the NetScaler RESTful API with Python and troubleshot complex web-application issues with Wireshark and cURL.

2018 – 2020

Citrix XenApp and XenDesktop Specialist

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Responsible for the development, optimisation and management of the Citrix XenApp/XenDesktop landscape. Migrated toward a Nutanix hyperconverged infrastructure, built PowerShell automation (including an automated VDI rollout script), worked with Ivanti Workspace Control and produced multiple designs (logical, technical and low-level).

2017 – 2018

Support Engineer, Operations (2nd line)

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Joined via a young-professional programme in the IRI Operations team. Routed incidents and changes through Topdesk, managed and monitored infrastructure with SCCM, administered Microsoft Active Directory (groups, policies, users, NTFS permissions), developed PowerShell scripts and resolved complex network and access issues.

2015 – 2017

Systems Administrator

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Broad hosting-provider role, from phone support to infrastructure builds: set up Microsoft Remote Desktop Services, a Linux ZFS shared-storage environment for KVM, and an OpenVPN service for admins and customers. Migrated large Microsoft Exchange mailboxes to Kerio Connect, monitored Linux servers with LibreNMS, configured Cisco switches and helped roll out a fully renewed IT infrastructure.

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