The Virtualization Battleground: OpenVZ vs. LXC vs. KVM in High-Availability Environments

Let’s be honest: most "Cloud VPS" providers are lying to you about performance. If you are running a high-traffic Magento store or a latency-sensitive SaaS application in Oslo, and you're relying on cheap OpenVZ containers, you are essentially gambling with your uptime. I’ve seen it time and time again—sysadmins debugging random 502 Bad Gateway errors, blaming Nginx, when the real culprit is a "noisy neighbor" on the host node stealing CPU cycles.

In the Norwegian hosting market, where reliability is valued above all else, understanding the architecture under your application is not optional. It is the difference between a sluggish site and one that handles the Datatilsynet's scrutiny and massive traffic spikes with ease.

The "Container" Trap: OpenVZ and the Myth of Burst RAM

For years, OpenVZ has been the darling of budget hosting. It’s container-based virtualization, meaning all guest instances share the host's kernel. It’s lightweight and dense. But for a Battle-Hardened DevOps professional, it’s a minefield.

The problem lies in how resources are accounted for. OpenVZ uses user_beancounters to limit resources. It introduces the concept of "Burst RAM"—memory you might get if the host isn't busy. But when the host gets busy (like during peak hours in Europe), that memory vanishes, and the OOM (Out of Memory) killer starts murdering your MySQL processes.

# Checking fail counters in OpenVZ (If you see numbers here, move hosts immediately)
cat /proc/user_beancounters 

# Look for the 'failcnt' column. 
# If it's > 0 on privvmpages, your malloc() calls are being rejected.

The Rising Challenger: Linux Containers (LXC)

LXC is gaining serious traction this year (2013) as a more standardized alternative to OpenVZ. It leverages kernel cgroups (control groups) and namespaces directly, without the heavy patching OpenVZ requires. It’s fast—bare metal fast.

However, LXC is still raw. We are seeing tools like the recently announced Docker project (currently in early beta v0.1/0.2) attempting to wrap LXC in a more user-friendly interface, but for production environments today, you are likely managing LXC with raw config files or libvirt. It requires a deep understanding of cgroup subsystems to ensure isolation.

Configuring LXC for Safety

If you are orchestrating LXC manually, you must define strict limits to prevent one container from starving the others. Here is a snippet from a production lxc.conf we used for a client in Stavanger:

# /var/lib/lxc/web_node_01/config

# Network isolation
lxc.network.type = veth
lxc.network.flags = up
lxc.network.link = br0
lxc.network.ipv4 = 192.168.10.20/24

# Cgroup Resource Limits (Crucial!)
lxc.cgroup.memory.limit_in_bytes = 4G
lxc.cgroup.memory.memsw.limit_in_bytes = 4G
lxc.cgroup.cpuset.cpus = 0,1

The Gold Standard: KVM (Kernel-based Virtual Machine)

This is where CoolVDS draws the line in the sand. While containers (LXC/OpenVZ) are great for density, KVM provides true hardware virtualization. Each VPS has its own kernel. If a neighbor panics their kernel, your instance keeps humming along. For database workloads (MySQL/PostgreSQL), KVM is non-negotiable.

Pro Tip: When using KVM, always ensure your provider uses virtio drivers for disk and network. This bypasses full emulation overhead, giving you near-native I/O performance. At CoolVDS, this is default.

Optimizing I/O on KVM

In a KVM environment, we can tune the I/O scheduler inside the guest, which is impossible in OpenVZ. For our SSD-backed storage, you should switch from the default CFQ scheduler to DEADLINE or NOOP to reduce latency.

# Check current scheduler
cat /sys/block/vda/queue/scheduler
# [cfq] deadline noop

# Change to noop for SSDs (add to /etc/rc.local)
echo noop > /sys/block/vda/queue/scheduler

Orchestration: Beyond Bash Scripts

Whether you choose LXC or KVM, managing more than five servers requires orchestration. In 2013, the debate is largely between Puppet, Chef, and the rising Python-based contender, SaltStack.

We recently deployed a cluster for a media agency using Puppet to enforce configuration consistency across KVM nodes. This ensures that every time we spin up a new CoolVDS instance, it is immediately hardened and compliant with Norwegian privacy standards (Personopplysningsloven).

Here is a basic Puppet manifest to ensure your web server is always running and optimized:

# /etc/puppet/manifests/site.pp

node 'web-01.coolvds.net' {
  package { 'nginx':
    ensure => installed,
  }

  service { 'nginx':
    ensure  => running,
    enable  => true,
    require => Package['nginx'],
  }

  file { '/etc/nginx/nginx.conf':
    source  => 'puppet:///modules/nginx/nginx.conf',
    notify  => Service['nginx'],
  }
}

Why Storage Speed Wins the War

You can have the best orchestration in the world, but if your disk I/O is slow, your application will crawl. This is why the industry is shifting away from spinning HDDs to Solid State Drives (SSDs). While standard SATA SSDs are great, we are closely watching the development of NVMe storage protocols (Non-Volatile Memory Express) which promise to bypass the AHCI bottleneck entirely.

Currently, CoolVDS leverages high-performance Enterprise SSD arrays. This low latency is critical when your data center is in Oslo and you are serving users in Tromsø or Bergen. Every millisecond of disk wait time adds up.

Database Tuning for SSDs

If you are running MySQL 5.5 on our SSD instances, ensure you configure InnoDB to take advantage of the high IOPS:

[mysqld]
# /etc/mysql/my.cnf

# Utilize the SSD IOPS
innodb_io_capacity = 2000
innodb_flush_neighbors = 0

# Maximize memory usage (70-80% of RAM)
innodb_buffer_pool_size = 6G
innodb_log_file_size = 512M

Conclusion: Architecture Matters

Don't fall for the "unlimited resources" marketing hype. In the cold reality of systems administration, isolation and dedicated I/O are the only metrics that count. Whether you are experimenting with the new lxc-create templates or sticking to the proven stability of KVM managed by Puppet, your infrastructure decisions today dictate your uptime tomorrow.

If you are ready for a hosting partner that speaks tcpdump and understands the importance of true hardware isolation, it's time to upgrade.

Don't let legacy virtualization kill your performance. Deploy a pure KVM instance with SSD storage on CoolVDS today and see the difference latency makes.