OpenVZ Containers: The Efficiency King or a Sysadmin's Nightmare?
If you have browsed WebHostingTalk lately, you have seen the offers: 512MB RAM VPS for $5/month. It sounds too good to pass up. But as anyone who has tried to run a heavy Java Tomcat stack or a busy MySQL cluster on these budget slices knows, there is no such thing as a free lunch.
The secret sauce behind these cheap offers is usually OpenVZ. Unlike full hardware virtualization (like Xen or the emerging KVM), OpenVZ is operating system-level virtualization. It’s lightweight, it’s fast, and in the wrong hands, it is a disaster waiting to happen.
I have spent the last week migrating a client off a congested node where their database latency was spiking every night at 20:00. The culprit? A neighbor on the same physical server running a backup script that hammered the shared disk I/O. This is the reality of container hosting.
The Architecture: Shared Kernel vs. Isolation
To understand the trade-offs, you have to look under the hood. In an OpenVZ environment, every container (VPS) shares the host node's Linux kernel. There is no hypervisor layer translating instructions.
- Pros: Zero emulation overhead. Native performance. You can modify files instantly.
- Cons: If the kernel panics, every customer on that node goes down. You cannot load your own kernel modules (forget about custom VPN tunneling modules unless the host enables them).
The "Burst RAM" Trap
OpenVZ introduces a concept called "Burstable RAM." Providers sell you "Guaranteed" RAM and "Burst" RAM. It looks generous, but technically, memory management in OpenVZ relies on user_beancounters (UBC). This is where many sysadmins hit a wall.
I recently debugged a Magento install on CentOS 5 that kept crashing with "Out of Memory" errors, even though free -m showed 200MB free. Why? Because they hit the privvmpages limit defined in the UBC, not the physical RAM limit.
# Checking fail counts on an OpenVZ container
cat /proc/user_beancounters
# Look at the last column (failcnt). If it's not zero, your provider is throttling you.
Pro Tip: If you see thefailcntrising forkmemsizeorprivvmpages, upgrade immediately. No amount of Apache tuning will fix a hard container limit.
Comparison: OpenVZ vs. Xen HVM
At CoolVDS, we are seeing a massive shift towards Xen (and testing KVM for future deployment) because serious businesses cannot afford the "noisy neighbor" effect.
| Feature | OpenVZ (Container) | Xen (Hypervisor) |
|---|---|---|
| Isolation | Shared Kernel (Process isolation) | Full Hardware Isolation |
| Swap | Fake (Virtual) | Real Dedicated Swap Partition |
| Performance | Near Native (if node is empty) | Consistent (Resources are reserved) |
| Kernel Modules | Restricted | Allowed (Load whatever you want) |
The Local Angle: Latency and Law in Norway
For our clients here in Oslo and across the Nordic region, there are two other critical factors: Latency and Data Sovereignty.
Routing traffic through cheap budget providers in the US adds 100ms+ latency. If your target market is Norway, you need to be peering at NIX (Norwegian Internet Exchange). A request from Trondheim to a server in Frankfurt is fast, but a server in Oslo is instant.
Furthermore, with the tightening enforcement of the Personopplysningsloven (Personal Data Act) and the vigilant eyes of Datatilsynet, knowing exactly where your data lives physically is becoming a legal necessity, not just a preference. OpenVZ nodes are often oversold and shuffled around. Dedicated Xen resources on CoolVDS infrastructure in Norwegian datacenters ensure you stay compliant and stable.
When to Use OpenVZ (Yes, it has a place)
I am not saying OpenVZ is useless. It is fantastic for:
- DNS Servers (Bind/NSD)
- Small VPN endpoints (if TUN/TAP is enabled)
- Development sandboxes that you spin up and destroy in minutes
But for your primary SQL database or high-traffic e-commerce site? You need dedicated I/O.
The CoolVDS Difference
We believe in transparency. We offer OpenVZ for development, but for production, we architect our solutions on robust Xen hypervisors with high-performance RAID arrays—including the new enterprise-grade SSDs for specific high-I/O workloads.
Don't let a shared kernel limit your growth. Stop fighting user_beancounters and start deploying on real hardware virtualization.
Ready to see the difference? Deploy a Xen instance with CoolVDS today and get true root access, protected by Norwegian privacy laws.