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Technical Briefing on tenantd
Problem Statement
CloudLinux offers enhanced tenant isolation features for servers, but it requires a forked kernel and incurs a monthly licensing fee. Users must also rely on CloudLinux’s update schedule for kernel patches and security updates, which can introduce operational delays and additional costs.
Implementation of tenantd
tenantd is designed to provide similar tenant isolation features to CloudLinux without the need for a forked kernel. It achieves this by leveraging cgroup v2, a feature that is already integrated into the stock Linux kernel. tenantd is developed and maintained by GetPageSpeed and is distributed through RPM channels. It is closed-source but free of charge.
Key features of tenantd include:
– Per-user CPU and memory caps
– Process and entry-process caps
– Per-user filesystem views
– Isolation for SSH and cron jobs
– Support for Multi-PHP
– MySQL governor capabilities
– Dedicated MariaDB instances for high-demand tenants
Limitations
tenantd does not support per-thread block-IO throttling for shared MySQL instances, a feature available in CloudLinux through kernel patches. Instead, tenantd handles high-demand scenarios by offering dedicated MariaDB instances to manage IO more effectively.
Practical Payoff
tenantd provides approximately 80% of the functionality of CloudLinux’s LVE-Governor without requiring users to switch to a forked kernel or pay licensing fees. This makes it an attractive option for cPanel hosts that do not need strict per-thread IO caps on shared MySQL databases.
Migration Process
The migration from CloudLinux to tenantd is facilitated by the tenantctl-migrate tool. This tool allows users to preview and commit the conversion process, typically completing the migration in under two minutes for a host with around 100 users, while causing minimal disruption to services.
Cost Comparison
tenantd is completely free, offering all its features at no cost, whereas CloudLinux charges between $7 and $18 per server per month. Additionally, tenantd users can retain the stock kernel, avoiding the operational costs and potential delays associated with CloudLinux-specific kernel updates.
Conclusion
tenantd presents a cost-effective alternative to CloudLinux, providing essential tenant isolation features without the need for a custom kernel or licensing fees. It retains compatibility with the stock kernel, offering a practical solution for server administrators seeking to optimize operational efficiency and cost.
