Mastering LXC Resource Allocation: CPU, Memory, and Disk Management

LXC (Linux Containers) provides lightweight virtualization for process and resource isolation, requiring minimal packages and low overhead. It is now part of the Linux kernel and represents a competitive lightweight container technology.

Important Resources for Virtual Machines

Resource management allocates resources from providers to users, addressing overload and dynamic demand. Key resources include CPU, memory, storage, and network; this article focuses on memory, CPU, and storage.

LXC Resource Allocation Methods

Directly Editing Configuration Files

LXC uses lxc.conf with key=value entries and cgroup for resource control. Editing this file allows direct resource adjustments.

Using Command‑Line Tools

The lxc-cgroup command manipulates cgroup parameters dynamically. Its syntax is: lxc-cgroup --name=NAME subsystem [value] -n, --name=NAME: container name

Subsystem: target cgroup subsystem

[value]: value to set

Example container name: cjhlxc.

1. View current resource list: # lxc-cgroup -n cjhlxc devices.list 2. Check CPU usage:

$ lxc-start -n cjhlxc -d
$ lxc-cgroup -n cjhlxc cpuset.cpus

Assign CPU 1 only: # lxc-cgroup -n cjhlxc cpuset.cpus "1" Alternatively, edit the config file: # sudo vim /var/lib/lxc/cjhlxc/config Add the line:

lxc.cgroup.cpuset.cpus = 1

Installing mpstat for Verification

Install sysstat inside the container and run:

$ sudo apt-get install sysstat
$ mpstat -P ALL 2

CPU 0 shows lower usage than CPU 1, but both can be utilized.

Fine‑Tuning CPU Allocation

LXC uses cpu.shares and cpuset.cpus. Adjust shares to control time slices:

# lxc-cgroup -n cjhlxc2 cpu.shares 512
# lxc-cgroup -n cjhlxc1 cpu.shares 1024

This gives cjhlxc1 ~66% and cjhlxc2 ~33% of CPU resources. LXC supports dynamic adjustment without stopping applications and can preempt idle containers.

Configuring Memory Resources

The memory subsystem provides reports and limits via two parameters: memory.limit_in_bytes: maximum memory (including cache) memory.memsw.limit_in_bytes: maximum combined memory and swap

Example

Set container cjhlxc memory to 320 MB using the command:

# lxc-cgroup -n cjhlxc memory.limit_in_bytes 320000000

Or edit the config file: lxc.cgroup.memory.limit_in_bytes = 320000000 Disable swap by adding:

lxc.cgroup.memory.limit_in_bytes = 300000000
lxc.cgroup.memory.memsw.limit_in_bytes = 300000000

Adding Disk Storage to LXC

Create a mount point on the host and mount a new disk:

$ sudo mkdir /var/lib/lxc/cjhlxc/rootfs/mnt/mydisk
$ sudo mount /dev/sdb1 /var/lib/lxc/cjhlxc/rootfs/mnt/disk1

Create a file inside the mount:

$ sudo touch /var/lib/lxc/cjhlxc/rootfs/mnt/disk1/abc

Start the container to apply the changes:

$ sudo lxc-start -n cjhlxc -d
$ sudo lxc-console -n cjhlxc

LXC Monitoring

List active containers: # lxc-ls --active Show container details: # lxc-info -n cjhlxc Monitor state changes with lxc-monitor.

Summary

LXC offers low‑overhead virtualization, easy CPU and memory adjustments via cgroup, and comparable performance to native environments. It cannot hot‑migrate, emulate different architectures, or provide strong isolation. The article compares LXC with other Linux virtualization technologies.